Philippe Cousteau

Article / Updated 04-20-2021

Osteichthyes (pronounced ah-stee-ick-thees) is a class of about 28,000 fish characterized (in most forms) by a bony skeleton, scales (some without), paired fins, a single pair of gill openings supported by bony gill arches each covered by an operculum, jaws, a mouth with many teeth, a swim bladder (air-filled sack) for buoyancy, paired nostrils, and external fertilization of eggs. Bony fish are generally broken down into two groups: Ray-finned fish: Ray-finned fish have fins supported by spines; the fins are moved by muscles in the body of the fish that do not extend into the fins. They (usually) have a pair of pectoral fins and a pair of pelvic fins, along with dorsal, anal, and caudal fins, and most look like, well, a fish — their bodies are oval-ish and tapered at each end. They breathe primarily through gills. And they have a lateral line — a row of organs that sense changes in water pressure, movement, and vibrations (kind of like the sensitive hairs in our inner ears) which helps them find prey and not become prey themselves. Lobe-finned fish: Lobe-finned fish have rounded fins (shaped more like your earlobes), which are supported by muscles and articulated bones (bones that meet to form joints). In other words, their fins are more like hands than typical fish fins, though the end of each fin has thin, bony structures that fan out from the core of the fin. These fins are thought to be the precursors of amphibian legs and feet. Lobe-finned fish also have two dorsal fins (instead of one), and they have both gills and lungs (though they’re not functional in certain species), which enables some of them to breathe on land or under water. As your mother told you when you experienced your first heartbreak, there’s always more fish in the sea. With bony fish, that means 28,000 species and counting. We can’t possibly cover them all, so we kept this discussion brief by describing the two groups (ray-finned and lobe-finned) and highlighting the common, the cool, and the weird in each group. Ray finned Actinopterygii (ray-finned fish) are, by far, the largest and most diverse group of bony fish. They include anchovies, angelfish, barracuda, catfish, cod, eels, flounder, flying fish, frogfish, gars, grouper, grunt, halibut, herring, hogfish, jacks, lionfish, mackerel, marlin, minnows, mullet, needlefish, perch, piranha, pompano, porgy, sailfish, sardines, sea bass, sea trout, seahorses, shad, sheepshead, snappers, snook, sole, sturgeon, swordfish, tarpon, triggerfish, toothfish, tuna . . . we could go on but we think you get the idea. But let’s look at some notable members of the group. Imagine an award show with categories for the smallest, biggest, fastest, and so on: Smallest: Stout infantfish are barely as long as the width of a pencil — females max out at about 8.4 millimeters long, while males grow to only 7 millimeters. They’re also the smallest and lightest of all known vertebrates. If you ordered a pound of stout infantfish from the menu, you’d get a plate of roughly 500,000 fish! Largest: The sunfish (Mola Mola) can grow to be over 2,268 kilograms (5,000 pounds). They live in warm water and look like a swimming fish head that has been smushed. Fastest: The black marlin has been clocked at a maximum speed of about 129 kilometers per hour (about 80 mph). Longest: The giant oarfish is a long serpent-looking pelagic fish up to eight meters (26 feet) long. They’re silver with a red mohawk looking fin. They cherish their privacy and are rarely seen alive. Coolest: The Antarctic icefish lacks hemoglobin in its blood, making it clear and less susceptible to freezing, sort of like anti-freeze, which is useful for any fish living in the frigid waters off Antarctica. Due to this lack of hemoglobin, they have huge hearts and almost four times the amount of blood as other fish. Weirdest couple: Female anglerfish have it going on! Living in the dark, deep ocean, these ladies have a dangling dorsal fin tipped with luminescent skin, which functions as a fishing rod protruding from the center of their head ending in a glow-in-the-dark lure just in front of their huge mouth full of teeth. And she has all the guys attached at the hip, seriously. Male anglerfish are usually much smaller than the females. When a male finds one of these lovely ladies, he attaches himself to her as a permanent parasite. After a while, he loses his eyes and all his organs except his testes, physically fusing his body with hers. Talk about a Stage 4 clinger! Females can carry around multiple mates. Cutest: Seahorses get by on their looks. Remember when we said most ray-finned fish look like fish? Well, seahorses are one of those exceptions. They swim around upright with what looks like a little armored body and quick moving fins. They have a tubular snout used for eating plankton and fish larvae. And it’s the male seahorses that carry around the fertilized eggs in a special pouch until they hatch — how adorable is that?! Father of the year: Speaking of caring fathers, the jawfish is a paternal mouthbrooder, meaning he holds the fertilized eggs in his mouth till they hatch (see the following figure). Every so often, he spits them out, a practice called churning, which keeps the eggs aerated, hydrated, and clean, thereby increasing the chances that more will hatch. All the while, he doesn’t eat a thing. Fortunately for him, the incubation period for the eggs is only five to seven days. Friendliest: Yep, fish can be friendly, and a perfect example is the grouper. Because of their large size (the goliath grouper can grow to be almost 800 pounds), these fish are not really scared of anything and are naturally curious. We have had many encounters with grouper fish over the years, and honestly, they are the Golden Retrievers of the sea. The grouper in the following figure actually took Ashlan on a tour of his home, following her along her entire dive and nudging her when she wasn’t paying him enough attention. Longest living: Orange roughy, brightly colored and slow moving, can live up to 200 years — that is, unless they’re eaten (by us). The problem with eating orange roughy is that they don’t reach sexual maturity until the age of 20, so they’re exceedingly susceptible to over-fishing, and they’re caught using the super destructive fishing method of bottom trawling. If you need another reason not to eat them, they’re often full of heavy metals, such as mercury, because they live a long time and bio-magnify toxins into their tissue. So next time you are at a restaurant and they offer you orange roughy as a special, just say no and feel free to tell the waiter (and the chef) why. Honestly, most people, even in restaurants, don’t know how bad and destructive catching some of these fish is. A little schooling goes a long way. Lobe-finned Sarcopterygii (lobe-finned fish) are a group of only eight living species with lobe-shaped fins, two dorsal fins, gills, and lungs (which aren’t functional in certain species). They’re broken down into two classes — coelacanths and lungfish. Coelacanths Thought to have gone extinct 66 million years ago with the dinos, a coelacanth was spotted at a fish market in 1938. Two extant (living) species are now recognized — the West Indian Ocean coelacanth and Indonesian coelacanth. Referred to as a living fossil, many scientists see them as a possible link between sea creatures and four-legged land animals, such as salamanders, newts, and lizards. Living as deep as 2,000 feet, these carnivorous fish sleep in caves during the day and hunt for prey (mostly octopus, squid, and cuttlefish) at night. They grow to be about 6 feet long and weigh up to about 200 pounds. In 2010, Laurent Ballesta led a confidential Gombessa expedition in Jesser Canyon, Sodwana Bay, South Africa, to capture the very first pictures of the coelacanth taken by a diver (–120 meters). This was possible thanks to the South African diver Peter Timm, who was the first to face the mythical fish locally named Gombessa. Discover more in the book, Gombessa, Meeting with the Coelacanth. Coelacanths have lungs during their embryonic development that stop developing as the fish grows and are barely noticeable (and non-functioning) in adults. They also have a rostral organ in their snout that’s part of an electro-sensory system and a hinged skull that enables the back of the skull to tilt up to enlarge the opening of the mouth. Lungfish As their name implies, lungfish can breathe air. Yep, they have either one or two lungs (depending on the species) to extract oxygen from the air, and they also have gills to extract oxygen from water. These are freshwater fish that live in rivers and lakes in Australia, Africa, and South America. And they’re big — most species growing up to 1.2 to 2.1 meters (4 to 7 feet) long. Lungfish have horrible eye sight, but their great sense of smell, lateral lines, and sensitive touch (with their pectoral and pelvic fins) make up for it. African lungfish can also go into a deep sleep (estivation) for up to two years — a slimy sleeping beauty.

Article / Updated 04-20-2021

Elasmobranchii (pronounced ee-laz-mo-brank-ee-ee) are a familiar subclass of fish that includes some of the most misunderstood and maligned creatures in the world—sharks, skates, and rays. They’re characterized by a rigid dorsal fin (the top fin) and have four to seven pairs of gill slits to breathe. They’re all carnivorous, feeding on everything from large marine mammals to small crustaceans, and they lack a swim bladder, equipped instead with an oily liver to maintain buoyancy. In contrast to the teeth of most vertebrates, which are locked into sockets in the jaw bones, elasmobranch teeth are attached to the jaw with fleshy tissue. Many species have rows of teeth that continue to be replaced—some may go through as many as tens of thousands of teeth in a lifetime. Selachiia: Sharks Sharks go way back. The first evidence of sharks dates to the Ordovician period 400 to 450 million years ago! Approximately 450 species of fish have the honor of being classified as sharks, and they range in size from about 20 centimeters (eight inches) to 12 meters (40 feet) long. They’re all predators and feed mostly on fish, seals, and whales, but some sharks, such as the whale sharks and megamouth sharks, feed on tiny plankton. Baby sharks are called “pups,” but even before they’re born, they’re not all sweet and cuddly. Some baby sharks eat their brothers and sisters who are growing slower while still inside their mother (talk about sibling rivalry!). Other species of sharks create extra eggs for the growing pups to consume. Both are examples of intrauterine cannibalism. Some scientists believe this practice is “survival of the fittest” to keep the species strong. The smallest of sharks is the dwarf lantern shark. Lantern sharks, as their name implies, are bioluminescent—able to produce their own light, which they use to ward off predators, blend in with the lighter background above them, and communicate when swimming in schools. On the other end of the size spectrum is the whale shark, which can grow as long as 40 feet and weigh up to 40 tons (see the following figure). While this whale shark could easily gulp down prey larger than humans, it prefers feeding on tiny plankton. So, the biggest fish in the sea eats some of the smallest food. Bull sharks, so named because of their short, blunt snout, wide body, and aggressive temperament (and because they often head-butt their prey before eating them), are unique in that they can live in freshwater or marine environments, sometimes swimming far upstream into a river or tributary (see the following figure). Among sharks, they pose perhaps the most serious threat to humans mostly because they like to swim in the same places humans do, not because they find humans particularly tasty. Mako sharks (see the following figure) are perhaps the fastest of the species and one of the fastest fish on the planet, attaining speeds of up to 74 kilometers (45 miles) per hour, fast enough to chase down its favorite food — the speedy tuna. The hammerhead shark gets the award for being the weirdest looking with an eye on either end of its mallet-shaped head. They feed mostly on small fish, octopus, squid, and crustaceans and can grow up to six meters (20 feet) long and weigh as much as 450 kilograms (about 1,000 pounds). Depending on the species, they are either solitary or school in enormous numbers. No section on sharks would be complete without mention of the baddest shark prowling the oceans — the great white shark, which can grow up to 6 meters (20 feet) long and weigh more than 2.5 tons (see the following figure). They have a varied diet of fish, crustaceans, seals, sea lions, other sharks, and even small-toothed whales such as orcas. Where do they live? Wherever they want. But seriously, you can bump into one just about anywhere the water temperature is between 12 and 24 degrees Celsius (54 and 75 degrees Fahrenheit). Some people are terrified of sharks and won’t even take a dip in the ocean because of them, but we love sharks. I (Ashlan) am particularly fond of them for their beauty, size, power, athleticism, diversity, and for all they do to keep our oceans healthy. We really want you to love and respect them, too . . . and, if you fear them, to stop being afraid. Sharks have far more reason to fear (and hate) us humans than we have to fear them. Yes, Jaws scared the “carp” out of all of us, and to his dying day Peter Benchley (who wrote the book) felt horrible for this. He later became a huge shark activist, but the damage had been done. Generations of readers and moviegoers were scared out of their swimsuits of sharks, especially the great white, and unnecessarily so. Sharks are not vicious murderers just waiting for you to wade past the buoys or paddle your surfboard or paddleboard overhead. Certainly, some animals kill for fun — namely dolphins, house cats, killer whales, leopards, honey badgers, and, of course, humans. But the vast majority of predators, including sharks, eat only when necessary. And, like many predators, sharks carefully calculate their return on investment—whether they’ll expend more energy attacking a healthy surfer or an injured seal, for example. That’s why sharks smell for blood. They’re on the prowl for the wounded and the sick, and they can go long stretches without eating, so they can afford to be picky eaters and wait for the right opportunity to come along. Nothing personal, but you’re not the first choice on their menu. In fact, scientists believe that shark attacks happen as a case of mistaken identity. Sharks can only tell what you are with their mouth (no hands to feel ya with) which is why most attacks are a single bite and release and thus not usually fatal. The sharks quickly realize that you aren’t their normal prey and they move on. Still afraid? Then check out the following table to put your chances of dying from a shark attack in perspective. Gauging the Risk of Death from Shark Attack Cause of death Average annual deaths in the U.S. Car accident 44,757 Gun deaths 36,000 Accidental poisoning 19,456 Falling 17,229 Bike accident 762 Air/space accident 742 Excessive cold 620 Sun/heat exposure 273 Bee, wasp, hornet stings 62 Lightning 47 Train accident 24 Dog attack 16 Fireworks 11 Spider bite 7 Snake bite 5 Shark attack 1 Not only are sharks much less dangerous than many people think, they also play a vital role in maintaining a healthy ocean. As apex predators, they keep the population of their prey in check, strengthen the gene pools of their prey, and reduce the spread of disease by eating the sick, weak, and injured. Lions, tigers, bears, and other apex predators perform the same service, but they don’t get the horrible rap that sharks do (and they also attack people every once in a while, just sayin’). Sharks also protect plants and help preserve plant-based ecosystems by reducing the populations of the animals that graze on those plants. And they do their part to sequester carbon. Philippe and I swim with all types of sharks all over the world. From dozens of Great Whites off Mexico, swarms of Grey Reef Sharks in the Marshall Islands, to Whale Sharks in La Paz and huge Great Hammerheads in the Bahamas — never once have we felt scared or threatened. But we are always cautious and respectful when we’re in the water with these extraordinary predators. The ocean is their home, not ours. Unfortunately, every year, sharks are killed for their fins and their meat — about 100 million a year (but that number could actually be anywhere between 63 million and 273 million sharks killed each year). On average, that means about 11,400 sharks are slaughtered every hour, whereas four people in the whole entire world die from shark attacks per year on average. Sharks have far more to fear than we do. Batoidea: Rays Rays are a group of about 500 species that live in ocean waters worldwide. They look like a shark that has been smushed into a pancake in the outline of a kite (see the following figure). While sharks propel themselves with their tail, rays propel themselves with elongated wing-like pectoral fins. Some rays have a whip-like tail tipped with a venomous barb. A ray’s mouth is usually on the underside of its body and, when viewed from certain angles, looks as though it’s smiling. Instead of pointy teeth like sharks, rays have evolved rounded teeth they use to crush and grind their prey, mostly mollusks, crustaceans, and small fish. Another difference from sharks is that rays have their gill slits underneath their body as opposed to the sides and take in water to breathe through large openings (spiracles) on the upper surface of the head. In addition, most rays have their eyes on top of their head. Most are benthic (bottom dwelling) but some species such as the manta ray are epipelagic (free swimming). Like sharks, males have a clasper they use to mate with the female which then almost exclusively gives birth to live young. Finally, rays are almost all marine. Rays are a diverse group that includes electric rays, stingrays, manta rays, and more. In this section, we cover a few of our favorites. Electric rays have a rounded body and range in length from less than 30 centimeters (1 foot) to about 2 meters (6 feet). They’re equipped with two large electric organs positioned on either side of their head that are capable of delivering a 220-volt shock — more than sufficient for stunning prey and fending off predators. They generally feed on small fish and invertebrates, so you’re pretty safe unless you happen to step on one. The largest ray is the giant manta ray, shown in the following figure, which has a “wingspan” of up to nearly 9 meters (30 feet). They’re commonly referred to as “devil rays” because of the two special flaps at the front of their heads called cephalic lobes, but devil rays are very sweet. They feed mostly on plankton, using those devilish horns to direct more water and food into their mouths. Eagle rays have beautiful spotted skin that produce the appearance of dappled sunlight as they swim through the water. Unlike most rays, they have a very long pronounced tail and have been known to launch themselves out of the water in dramatic displays, spinning and flipping in the air. Last on our list of rays is the most unique of the group—the sawfish, also referred to as a carpenter fish. Granted, it looks more like a shark, but its mouth and gills are positioned on its underside, and it has wing-like fins characteristic of a ray. Its coolest feature is its long snout rimmed with exposed teeth. Batoidea: Skates Skates are members of the same subclass as rays, and they look like rays, but they have a few key differences. While rays are more diamond shaped, a skate’s body is more triangular or rounded, and they often have a pointy nose. Skates also have thicker, wider tails with sharp spikes that run along the middle of the tail and up their backs (no barb at the tip). Skates have small teeth to eat prey, in contrast to the rounded teeth rays use to crush and grind their food. While rays swim in both shallow and open water, skates typically hang out near the bottom and often hide in the sand. Also, instead of live births, skates lay eggs in a leathery case called a mermaid’s purse. Unfortunately, skates are struggling to survive. The International Union for Conservation of Nature (IUCN) listed the common skate as an endangered species in 2000 and as a critically endangered species since 2006.

Article / Updated 04-20-2021

While gastropod means stomach on a foot, cephalopod means head on a foot, but with these mollusks, the pod (foot) has evolved into many prehensile arms/tentacles, which may be equipped with suction cups, hooks, or gooey mucus to catch prey and perform other functions. Yes, we’re talking octopus and squid, and their close cousins, the nautilus and cuttlefish. Most cephalopods have eight to ten arms, but some (such as the nautilus) have as many as 90. Now that’s a lot of handwashing! If you look at a bivalve and a cephalopod side by side, you’d never imagine they were in the same family. Not even close! Every cephalopod has a sophisticated brain, three hearts, good eyesight, a system of jet propulsion, prehensile arms, a sharp beak, and (in most species) an ink sac for self-defense — whereas a clam is a hunk of flesh sealed in a shell that can attach itself to rocks and sips through a straw. Most cephalopods lack the distinct shell that’s characteristic of most mollusks. One exception is the chambered nautilus, which has a well-developed shell with air-filled chambers to keep it afloat. The cuttlefish, which kinda looks like a nautilus without an external shell has an internal, elongated, saucer-shaped shell called a cuttlebone, which is often sold at pet stores as a calcium source for birds (which seems kinda wrong, btw). The squid has a long, thin, internal shell called a pen. In this article, we introduce you to the four most common members of the cephalopod family. Octopi If aliens exist on this planet, they’re octopi or octopuses (both spellings are acceptable, by the way). The octopus is regarded as one of the most intelligent creatures in the sea, and the most intelligent invertebrate on Earth thanks to its large brain. In fact, the brain-to-body ratio of the octopus is the highest of all invertebrates and greater than that of many vertebrates. It even has a group of nerves that act brain-ish for each arm, enabling the octopus to move them independently. The octopus is also a tool user and can learn and remember. (Full disclosure, they’re Philippe’s favorite animal—can you tell?) Moving on to the body, an octopus has eight arms, each of which has two rows of suckers used to capture and hold prey and to stick to smooth surfaces. The arms lead to a skirt, in the middle of which is their mouth (beak). With three hearts, they have lots of love to give. One heart pumps blood through the body, while the two small hearts pump blood to the gills. Their bodies are very malleable, allowing them to squeeze into super tight spaces — as long as their beak fits, they can make it, bringing a whole new meaning to the phrase, “If I fits, I sits.” Compared to bivalves, their sex lives are ultra-conservative. Males remain males and females remain females their entire lives. As soon as the male passes sperm to the female to fertilize her eggs, the female becomes a devoted, die-hard mother . . . literally. For example, the giant pacific momma octopus lays her eggs and attentively watches over them, keeping them clean, aerated, and protected for up to ten months, during which time she doesn’t leave and doesn’t eat. She usually dies shortly after her eggs hatch. Octopus fathers don’t fare much better — they often die after mating (talk about deadbeat dads!). An octopus will always beat you at a game of hide and seek. They’re able to change their color and texture to match their surroundings to a T. But the mimic octopus has everyone beat; it can even change its shape to impersonate other creatures such as a flounder, a lionfish, a sea snake, or even a tube worm. Hey, do you guys hire out for parties? Honestly, we could write an entire chapter or even a whole book about octopi, given how fascinating they are. Just look at how adorable the dumbo octopus is, and the mating ritual of the Argonaut Octopus is something we just can’t talk about in a book for family audiences. So much to say, but so little time. Squid Squids look a lot like octopi, but they’re different in many ways, including the following: An octopus is smarter than a squid, but squids are better swimmers. An octopus has a roundish body, rectangular pupils, and eight arms, whereas a squid has a triangular body with a fin on either side, round pupils, eight arms, and two longer tentacles (with suction cups only at the tips). The arms of an octopus are more flexible than those of a squid, enabling them to walk around and to hold and move objects. A squid has a rigid internal structure, called a pen, that runs along its mantle and provides support; an octopus does not. Octopi generally hang out on the seafloor eating crustaceans and other benthic prey, while squid prefer the open ocean, feeding on shrimp and small fish. A squid’s self-defense mechanism involves expelling a cloud of ink that serves as a smoke screen, whereas an octopus relies more on camouflage or squeezing its body into a hollow object or crevice, though in desperate situations, an octopus can ink, too. Octopi reproduce as partners and attend to their eggs for up to a year until they hatch, whereas squids mate in large groups and leave their fertilized eggs attached to rocks or corals to fend for themselves. Octopi are generally solitary, whereas squids may live alone or in groups. Squids range in size from about 16 millimeters (less than one inch, and so cute) up to 22 meters (about 72 feet, and terrifying) when stretched out. Some cool species of squid include the glass squid — almost fully transparent except for its eye balls (though its eye lids act as an invisibility cloak); the vampire squid, which can turn itself inside out to avoid predators; and the Humboldt squid, which can pulse its body with flashing red and white bioluminescence. Yowsa! Giant squid The giant squid is about eight meters (26 feet) long, but with its tentacles stretched out, it may reach 22 meters (72 feet) in length. These massive creatures live in the deep ocean, and scientists still don’t know much about them. Most of what’s known has been gathered from studying carcasses that have washed up on beaches or been brought in by fishing boats. Based on the limited information available, we know that they eat shrimp, fish, and other squids. We also know that they engage in defensive epic battles with whales and sharks (that like to eat squid), based on the fact that whales and sharks have been observed with what look like giant squid hickeys all over them. Because they live in the deep sea, giant squid have giant eyes. We’re talking BIG, as in largest in the animal kingdom — about 10 to 12 inches in diameter (the better to see you with my dear!). Researchers also think that giant squid live only about five years, meaning they must grow like weeds, and that they mate only once, so they’d better make it count. However, while the giant squid may be the longest, it may not be the largest. The colossal squid is shorter but weighs twice as much. One colossal squid on display at the Ta Papa Museum of New Zealand tips the scales at 490 kilograms (just over 1,080 pounds) while an average Giant Squid weighs in at around 275 kilograms (606 pounds). The beak of the colossal squid is the largest of all among mollusks, and their eyeballs are about the size of soccer balls. Even with their massive size, the giant and colossal squid are the preferred prey of the deep diving sperm whale. And (fun job), some scientists study the undigested beaks of these squid in sperm whale stomachs to gather additional information about the species. That would be one colossal and very smelly day at the office. Cuttlefish Cuttlefish, also known as cuttles (no, not cuddles, although they look kind of cuddly), are sort of a cross between a squid and an octopus but with a more compact body. Like an octopus, a cuttlefish has a big brain and is a master of camouflage. Like a squid, it has eight arms and two longer tentacles and its head and body are tapered, more like a torpedo. Cuttlefish are unique in that they have an undulating fringe running along their sides and a cuttlebone to help with buoyancy, which enables them to hover. Another unique feature is their pupils, shaped like a “W,” which enables them to see in front of and behind them at the same time. They tend to live in deep water during the winter and in the shallows over the summer months, and they live only one or two years, dying shortly after mating. The Giant Cuttlefish lives in the waters around Australia. These large cuttles can grow to have a mantle length of about 50 centimeters (20 inches) and weigh around nine kilograms (about 20 pounds). That’s a lot to cuddle! They come back every season to the same rocky shores of southern Australia and mate, lay eggs, and then die. When the next generation hatches, they head off into the world (not much is known about where they go or what they do), but they always return to the same area to mate, lay eggs, and perish (cue up “Circle of Life” from The Lion King). Nautilus If a snail, a shrimp, and an octopus, had a baby together, it would look like a nautilus. The nautilus has a spiraled shell like a snail, but it’s sectioned off into chambers containing air to make the nautilus buoyant, enabling it hover in the water. As the nautilus grows and expands its shell, it creates new chambers. It has a face like a shrimp and arms like an octopus — actually about 90 tentacles that are grooved and secrete mucus to capture food and hold onto stationary objects when resting. Compared to octopi and squid, the nautilus doesn’t have the greatest vision, relying more on their sense of smell to find food. They’re nocturnal (active at night), making daily migrations up and down the water column. They live much longer than the other cephalopods (up to 20 years). Unfortunately, their shells are highly prized and because they don’t reach sexually maturity until they’re 10 to 15 years old (and even when they do, females lay only about ten eggs max), their population has declined significantly and will require a long time to bounce back. And because they need a hard shell to survive, they’re also threatened by ocean acidification. Thankfully, they’re a protected species, though poaching still happens. The nautilus is considered a living fossil, because it has changed very little over the 500 million years it has been around (in some form). Today, they live in the waters of the Indo-Pacific, hovering above reefs at depths of about 100 to 300 meters (330 to 990 feet). They can’t go much deeper, because the pressure would crush their air-filled shells. Not a good way to go.

Article / Updated 04-20-2021

Bivalves are headless mollusks with a hinged, two-part shell, sort of like castanets. They’re very diverse, boasting a membership of more than 15,000 species divided into four main groups—clams, oysters, mussels, and scallops—generally based on where they live and the shape of their shells. Clams prefer an infaunal lifestyle, buried in the sand or silt, whereas mussels, oysters, and scallops live a more epifaunal lifestyle (on or above the seafloor). Regardless of whether they’re in-ground or above-ground, they have specialized gills that serve two functions — to extract food and oxygen from the water. They play a key role in cleaning the water and, fortunately, live in or near just about every body of water—oceans, lakes, ponds, rivers, and streams. Bivalves lead interesting sex lives. Clams and other burrowers tend to be dioecious, meaning they’re male or female their entire lives. Many scallop species are serial hermaphrodites, able to produce male and female gametes (sperm and eggs) their entire lives. Various oyster species are protandric hermaphrodites — males in their youth and then changing to females and staying that way as they get older (you go, girl). European oysters are rhythmical consecutive hermaphrodites, changing back and forth over the course of their lives. Clams If you’ve been to the ocean, you probably had a close encounter with a clam, although you may not have noticed, because they usually bury themselves in the sand for safety. To breathe and feed, they extend a long double-tubed siphon just above the surface of the sand that works sort of like a snorkel. One tube draws in water containing food and oxygen, and the other expels water, carbon dioxide, and wastes. Unlike oysters and scallops that move around on the seafloor at least a little, most clams restrict their movement to digging down and digging out. They use their mollusk foot less as a foot for locomotion and more as a shovel for digging. They also have two powerful adductor muscles located on opposite ends of the shell to close their home up tight when they feel threatened and to seal in the moisture in case they get stranded on shore. Most clams are filter feeders, although some supplement their diets by establishing symbiotic relationships with algae (in shallow water) or chemosynthetic bacteria (in deep water or areas that are high in sulfides). Giant clams are somewhat famous for their symbiotic relationship with algae. In fact, they’ve been referred to as “greenhouses for algae”—directing beneficial light to the mantle, where the algae hang out, but because too much light can be harmful to algae, the clam’s filter also redirects harmful light wavelengths away from the algae, making said algae feel right at home. Maybe this is why the giant clam is the largest of its kind. It can grow to be more than three and a half feet across and weigh more than 400 pounds! Oysters Oysters are awesome. You can eat them, build reefs with them, harvest their pearls to make beautiful jewelry, and even use them to clean the ocean. In fact, they’re top-of-the-line water filters! A single oyster can clean two to three gallons of water an hour, and they never get tired or break down. It’s no wonder conservationists and habitat restoration projects use oysters all over the world to quickly and naturally clean up dirty water and restore ecosystems. (Check out the “Billion Oyster Project” off NYC in the Hudson River.) Oysters are actually a subclass of saltwater clams but with irregularly shaped shells, which is how you can tell an oyster from a clam, a mussel, or a scallop. Those other bivalves have smoother shells with both halves matching pretty closely. Oyster shells are irregularly shaped and rougher. Their outer surface looks more like a bad concrete job but they can produce the most beautiful pearls on the inside. You can tell the color of a pearl before you even open the oyster by looking at its “lip”—its outer edge, because they form pearls out of the same material (nacre) they use to create their hard inner shells. These inner shells are the source of “mother of pearl,” which is used to create jewelry and adorn other objects. Mussels Mussels hang out in freshwater lakes, streams, creeks, and rivers, along with the intertidal zone, where ocean meets land. They’ve been cultivated in Europe since the 1400s for food (steamed in a white wine sauce with a side of French fries, please). In marine environments, mussels are often sessile, anchored to rocks in high-flow areas with their byssal threads, as explained in the nearby sidebar. They’re filter feeders, playing an important role in keeping the water clean. Anchors away! Some bivalves, mussels in particular, anchor themselves to a substrate using byssal threads, sort of like the material spiders use to create their sticky webs. After its juvenile stage, during which it floats around, a mussel uses its foot to attach itself to a solid surface (a rock, dock, cliff, mangrove root, oil tanker, or other solid object submerged or regularly doused with water), excretes a sticky plaque that holds it in place, then excretes a collagen-based protein from its byssal gland (in its foot). The mussel may create hundreds of these threads. It can then relax its foot, or even retract it, so it doesn’t need to waste energy trying to hold on. Young scallops can use byssal threads, too, but more conservatively, often affixing themselves temporarily to a substrate using a single byssal thread. Scallops Scallops have two fanlike shells joined by a straight hinge, which, along with the muscle inside that joins the two shells, enables them to “swim” short distances. Okay, it’s not really swimming; it’s more like a clapping motion that propels them through the water, but it gets them where they’re going. If you’ve never seen a scallop swim, head to YouTube right now and watch a clip. Scallops are also unique in that they have two rows of light-sensing organs, like eyes, arranged along either side of the scallop’s opening.

Article / Updated 04-20-2021

The largest group in the mollusk family (accounting for about 80 percent of all mollusk species), is the class Gastropoda, which literally means a stomach with a foot on it. The name strikes us as more than a little demeaning, not to mention inaccurate—after all, snails and most slugs have easily recognizable heads and a complex anatomy, including a liver, lung, heart, kidney, a primitive brain, and, yes, a stomach. In addition, they’re incredibly diverse. Gastropods are one of the few groups that have members living in all three main habitats—land, sea/ocean, and freshwater. As a group, they also have a varied diet. Depending on the species, they may be herbivores (plant eaters), scavengers, carnivores, or even internal parasites. These diverse creatures come in many sizes, some with shells and some without, but they all have a single “foot” they use mostly for locomotion. To move, they excrete mucus and contract their muscles in waves to slide over the surface of hard objects. Think of it as skating over ice that you create in front of you as you move in a certain direction. In this article, we break the family of gastropods down into two groups—snails (with external shells) and slugs (mostly without external shells). Snails Snails are gastropods that carry their homes on their backs. Many types can retract completely into their homes headfirst and seal them shut with an operculum (a thin, rigid disk attached to the foot of most snails). This door, which is a little softer than the shell, keeps predators out and moisture in, giving them a much wider travel range and enabling them to survive dry conditions. When you hear the word “snail,” you probably think of the archetypical snail with the spiral shell, but snails are far more diverse, as you’re about to discover. In the following sections, we introduce you to several different types of snails, some of which you may never have imagined being snails. Abalones Abalones, which account for about 60 to 100 gastropod species, are edible gastropods covered by a bowed shell that looks sort of like a flattened helmet with a line of holes along one side used for breathing and excreting wastes. The inside of the shell is lined with mother of pearl, which is commonly used in jewelry and to adorn other objects. Abalones also produce pearls, although they rarely receive much credit for doing so. Conches Conch is a general name that refers to medium-to-large mollusks that have a very angular shell with a wide lip. These are the shells you hold up to your ear to hear the sound of the ocean or you blow into to produce a loud sea call (which takes a lot of practice, trust us). Conches have some of the most creative names, such as queen conch (shown), dog conch, and horse conch, the latter of which is a giant predatory gastropod. When it eats something, well . . . it just looks darn nasty—like a massive tongue with no mouth or body slurping something up. Some conches can produce pearls, which are regarded as some of the rarest and most valuable pearls in the world (even though they’re not a “true pearl” but a calcareous concretion from the conch). Who knew? Cone snails Cone snails account for nearly 500 species of venomous, predatory sea snails each equipped with a harpoon containing a large collection of toxins. When its prey gets close to a cone snail, the cone snail fires its harpoon, piercing and the paralyzing (or killing) it, which it then swallows whole. Cone snails are cone shaped (of course) with a long, linear aperture (opening), as shown. Cowries Cowries have a smooth, glossy, domed shell with a long narrow opening. Their mantle has two special folds that the cowrie can wrap around the outside of the shell. These folds are covered with papillae (fleshy, hair-like projections) that may serve as camouflage or enhance respiration. Cowry shells are highly prized among shell collectors and have even been used in days long past as a form of currency. Limpets Limpets have a thick, conical shell and a strong, muscular foot. The shell is difficult for predators to grab hold of or crack, and the limpet uses its foot to draw itself tightly against rocky substrates, making it difficult to pry from the surface. Slipper limpets often live in stacks, like upside-down saucers. Where they are in the stack influences their sex. A large female is usually at the bottom with a small young male on top. When the male releases his sperm, it drops down to fertilize the female’s eggs. Limpets between the top and bottom may be male or female. Periwinkles Periwinkle is a name used loosely for all small freshwater and marine snails, but true periwinkles are marine snails that can be found in the ocean, on rocky shores, in estuaries and mud flats, and on the roots of mangrove trees. These sweet little gastropods have a small spiral shell built to withstand the constant beating on waves. They are also the favorite food of many seabirds—ducks, in particular, love them! Whelks Whelks are predatory snails that use their radula to drill through the armor of their prey (such as the shell of a mussel) to eat the soft flesh inside. They can also use their foot to take hold of a bivalve (such as a mussel or clam) and use their own shell as a wedge to pry open the shell. The whelk’s shell is similar to that of a conch.. Sea slugs and sea hares Sea slugs and sea hares are basically homeless snails. At some point in their evolution, they lost their shells, though many species have a tiny internal shell or a small external shell that barely covers their body. What’s cool, though, is that without shells to protect their soft bodies, they’ve evolved several interesting and effective self-defense mechanisms — camouflage; the ability to collect venom from what they eat and use it on their enemies; bold, bright colors to make them look venomous (regardless of whether they truly are); and the ability to detach a part of their bodies (as some reptiles do) and grow them back later. Now, if you’re thinking, “Slugs, yuck!,” you may be surprised to find out that more than 3,000 species of sea slugs called nudibranchs (which means “naked gills”) include some of the most diverse, colorful, and ornate creatures in the sea. If there were a beauty contest for marine animals, a nudibranch would probably claim the crown year after year. Some nudibranchs look like florescent hedgehogs, some look like glow-in-the-dark slugs on acid, and some look like gorgeous neon Flamenco dancers. All in all, they’re beautiful underwater gems. Seriously, we could do a whole giant coffee table book on dazzling nudibranchs. Sea hares are very similar to sea slugs, but they have large tentacles that resemble the ears of hares (rabbits), and they have wing-like structures they use for swimming. Some also squirt inky substances that look like a smoke screen but are thought to stimulate food receptors in predators, so they try to eat the substance while the sea hare makes its escape.

Article / Updated 04-20-2021

An ecosystem is a biological community of organisms interacting with their physical environment as a whole. Take a tour of three of the ocean’s varied ecosystems and some of the plants and animals that call them home. Swimming through Kelp Forests Imagine flying free through a giant forest surrounded by beautiful colors and bizarre, extraordinary animals. That’s what it’s like to swim through a kelp forest. While we may call them kelp forests, kelp is not technically a plant like a tulip or a tree. In fact, kelp is a multi-cellular algae that just looks like a plant. What distinguishes it from a plant is that plants have a vascular system to transport water and nutrients, whereas every cell in kelp is responsible for absorbing its own water and nutrients. Smaller gatherings of kelp are called kelp beds. Kelp thrives in cool/cold (from 42 to 72 degrees Fahrenheit), nutrient rich, and relatively shallow (two to 30 meters or 6 to 100 feet deep) water. It attaches itself to the seafloor with small rootlike structures called haptera or holdfasts. The kelp stays vertical in the water column thanks to gas filled floats (like tiny buoys) at the top of their stipes (comparable to stalks) or where each blade (the leafy part) branches off. Some kelp can grow up to 18 inches per day and reach up to almost 50 meters (150 feet) long. These underwater forests are high in diversity. Like terrestrial forests, they can be divided into three layers, which are a little different for kelp forests —the canopy lying on the surface, the subcanopy or understory below the surface, and the forest floor where the kelp is anchored. The canopy is home to small crustaceans, snails, sea slugs, larvae of many types of marine animals, and juvenile fish of all sorts. You’re likely to see sea otters, seals, sea lions, and a variety of birds that frequent the area to feed. The subcanopy is home to fish, sharks, squid, and, in Southern Ocean kelp forests, one of my (Philippe’s) favorite creatures, the leafy sea dragon. On the forest floor, you’re more likely to see snails, starfish, oysters, lobsters, crabs, and my bestie, various species of octopus. As quickly as kelp forests grow, they can be destroyed. Global warming is a huge problem. Other threats include pollution, overfishing, invasive kelp species, and voracious sea urchins. A group of sea urchins can destroy entire kelp forests at a rate of 30 feet per month. Fortunately, urchins are a delicacy to sea otters, which eat 20 to 30 percent their body weight in food every day. Unfortunately, sea otters are facing their own challenges — from not enough fish to eat and increased pollution to human related disease and even poaching. The absolute cutest activity that takes place in kelp forests (and maybe in the entire ocean) is this: Sea otters wrap their babies in kelp so they don’t drift away while the mother hunts or takes a well-deserved nap. Swirling in Sargasso: A Sea without Borders The Sargasso Sea is an area in the Atlantic Ocean where vast mats of a unique brownish-gold seaweed called sargassum live. Like kelp, sargassum has gas-filled bladders that make it float. Unlike kelp and other seaweeds, it’s holopelagic, meaning it spends its whole life (“holo”) floating in the pelagic zone (the water column) without needing contact with any land form and reproducing vegetatively (new plants grow from fragments of parent plants). Pretty cool, huh? The Sargasso Sea is also the only sea without a land boundary. Sargassum gathers in and around the North Atlantic Gyre, a huge, swirling body of water off the eastern coast of the United States that spins due to ocean currents. These swirling currents concentrate the sargassum into enormous mats (called windrows), which can be hundreds of meters long. Based on satellite images, scientists estimate the biomass in the Sargasso Sea to be around one million tons. The Sargasso Sea is an oasis in the open ocean for all types of creatures, including sea turtles, whales, sharks, fish, crabs, snails, octopus, squid, worms, shrimp, nudibranchs, and more. Some animals are specially adapted to live among this floating haven, such as the iconic Sargassum Angler Fish, which not only blends into the surroundings but also has special fins that enable it to climb through the seaweed (see figure). However, while some creatures spend their whole life in the sargassum, others just take a break while passing through. The most famous of these are sea turtles. After emerging from their nests, sea turtles scurry down the beach into the ocean. In the Atlantic, many species of sea turtles then swim as fast as they can out into the Sargasso Sea to spend their early years hiding amongst the relative safety of the sargassum mats before they are big enough to venture out again into the open ocean. Grazing in the Seagrass Meadows Unlike kelp and sargassum (both seaweeds) seagrass is a bona fide plant, complete with a vascular system (a network of veins to move nutrients and dissolved gases throughout the plant). In fact, it’s the only angiosperm (flowering plant) in the ocean. The flowers are usually borne underwater, and pollination occurs underwater as well (in most cases). Seagrass also has a true root system, as opposed to a simple holdfast like kelp. The root system anchors the plant to its substrate and acquires nutrients for the plant as well. Similar to lawn grass, sea grass roots commonly send out rhizomes (underground shoots that sprout more grass). This root/rhizome system creates a dense, interwoven mat that holds the grass and seafloor in place, thereby literally anchoring the entire ecosystem. Seagrass can be found nearly everywhere in the world except Antarctica. It grows in both salty and brackish water as long as the water is shallow and can vary in size from small mats to enormous meadows that resemble fields of underwater wheat. Botanists estimate that globally these sea grass fields produce more vegetation than all the wheat fields of the U.S. grain belt combined. Some of these fields are even large enough to be seen from space! Seagrass fields are extremely important in providing nursery and adult habitat and feeding grounds for many species, from small invertebrates all the way up to turtles, birds, crabs, and large fish. Most seagrass grazers use the broken up and degrading leaves as their food source. Others, such as the sea turtle, the manatee (see the following figure), and its relative the dugong, eat the entire plant — and a lot of it, too. One large, hungry manatee can gulp down almost 100 pounds of seagrass a day! In addition to providing food and shelter, the seagrass helps reduce erosion, filter water, release oxygen into the water, and extract and sequester carbon dioxide. With all these benefits, seagrasses are thought to be one of the most valuable ecosystems in the world, just behind coral reefs, estuaries, and wetlands. One hectare of seagrass (about two and a half acres) is estimated to be contribute over $19,000 per year of value to the global economy.

Article / Updated 04-19-2021

The ocean’s water column (a conceptual pillar of water measured from the ocean’s surface to the seafloor) is often divided into five zones—the epipelagic, mesopelagic, bathypelagic, abyssopelagic, and hadalpelagic zones. The divisions generally correspond to differences in depth, amount of sunlight, temperature, pressure, nutrients, and organisms that live in those zones. In the following sections, we take a deep dive into each of the ocean's five vertical ocean zones. Skimming the surface: The epipelagic zone The epipelagic zone (commonly referred to as the sunlight zone) is the top 200 meters (about 650 feet) of the ocean, where enough sunlight is available for plant life to grow and support a large, diverse population of marine life. Because it forms the ocean’s surface, the epipelagic zone experiences greater variations (compared to the other vertical zones) in temperature and other conditions due to climate, local weather patterns, and proximity to large land masses. Who lives here? Lots of plankton (tiny plants and animals that float, as shown); nekton (tiny plants and animals that swim); jellyfish; sea turtles (shown); a variety of fish including tuna (shown), marlin, salmon, and sharks; and cetaceans (dolphins and whales). It’s not as though these zones are sectioned off like office cubicles. Plenty of animals roam freely from one zone to another. Animals that need to breathe air, such as sea turtles, dolphins, and whales generally hang out closer to the surface just so they can get their heads (or noses or blowholes) above water regularly. Others prefer the shallower water for other benefits, such as food, light, warmth, and lower water pressure. Dimming the lights in the mesopelagic zone Just below the epipelagic zone is the mesopelagic zone (commonly referred to as the twilight zone). This is the region spanning 200 to 1,000 meters (650 to 3,300 feet) below the surface, where some sunlight still penetrates, but not enough for photosynthesis. To feed, most animals in this zone move toward the surface. Others eat whatever detritus (table scraps) and organic matter fall from the epipelagic zone, or they just eat their smaller or weaker twilight zone neighbors. Some animals in this zone have evolved the ability to produce their own light — a trait referred to as bioluminescence (creating light through biochemical processes). Instead of carrying a flashlight to find their way in the dark, they are the flashlight. Although scientists aren’t quite sure about the purpose of this superpower, they think it might be used to ward off or evade predators, detect or lure prey (ooh, shiny light!), or communicate with members of their own species. Counter-illumination: Some sea creatures that can bio-luminate may use this skill as camouflage, illuminating their soft underbellies to blend in with light coming from the surface, while the tops of their bodies remain dark to blend in with the darkness below them. This application of bioluminescence, called counter-illumination, protects the creature from predators above and below. When predators from below look up, all they see is light. When predators from above look down, all they see is darkness. Take that, camo pants. Life starts to get a bit weird in this zone. Here, you’re likely to start bumping into cool fish like the lanternfish, hatchetfish, and barbeled dragonfish all of which can produce their own light. You can also find species of bristlemouths. These fish, generally no larger than your finger, are not only thought to be the most common fish in the ocean, but also the most common vertebrate on Earth — more abundant than humans, chickens, and rats combined. Let that sink in for a second. Some marine mammals and sharks can also be found here, but most will stay in the mesopelagic only for relatively short periods before returning to the surface. Swordfish, ctenophores (see below) and siphonophores (jellyfish relatives), and firefly squid are other interesting animals that can be found in this zone. Taking a deeper, darker dive into the bathypelagic zone Just below the mesopelagic zone is the bathypelagic zone (also called the midnight zone), which extends from 1,000 meters to 4,000 meters (3,300 to 13,000+ feet) below sea-level. No sunlight penetrates this zone, and the temperature is relatively constant at a very chilly 4 degrees Celsius (39 degrees Fahrenheit). Animals in this zone prey on other bathypelagic organisms or grab whatever rains down like manna from above. Some creatures in this zone migrate closer to the surface to feed at certain times of day. The creatures that live here are too insane to make up, but they’re not the most colorful — just about everything is black or red, which makes everything invisible in water at these depths. (Certain wavelengths are filtered by water faster than others. Because red light has the longest wavelength and is absorbed quickest, once you go deep enough, anything red appears black.) If you cut yourself diving at around 60 feet deep, your red blood may appear purple and, if you go any deeper, even black. Of course, we’re not recommending that you poke your finger when you’re diving, but if you happen to suffer a small cut underwater at that depth and you’re looking for a cheap thrill . . . . Calling this zone their home are the weird and wonderful barreleye fish, giant isopods, viperfish, vampire squid, and anglerfish. Occasionally you can find sperm whales here, and if you’re really, really lucky, you can see one battling a giant squid (of course if you do, take a picture because no one has captured that epic battle on film yet). The deepest diving marine mammal, the Cuvier’s beaked whale, can also reach this zone. This elusive and strange-looking animal holds the record for the longest mammalian dive, plunging up to 3,500 meters (11,480 ft) deep (that’ll make your ears pop) in search of deep-water cephalopods and squid. Many animals in this zone and deeper have adaptations to allow them to eat almost anything, including prey much larger than them. Gulper eels have specialized jaw structures that enable them to open their mouths incredibly wide. Sharks and their relatives, including the Greenland shark (which can live for 400 years), ghost shark, frilled shark and goblin shark can sometimes also be found in this zone, as well as the deepest living octopus, the dumbo octopus shown (although some say it can be found at even greater depths). Delving into the abyss: The abyssopelagic zone One step down from the bathypelagic is the abyssopelagic zone (also called the abyss), extending from 4,000 to 6,000 meters (13,000+ to nearly 20,000 feet) below the surface. Imagine totally dark, near-freezing temperatures (though stable), and super high pressure. For animals adapted to these harsh conditions, the pressure is no problem. Unlike animals with gas-filled organs (such as lungs and swim bladders) that would be crushed at these depths, deep-sea creatures are pretty much made up of tissue and fluid. While the high pressure may limit species diversification, it isn’t the hardest part about living here. The more challenging factor is the scarcity of food. Generally, the further down you go, the fewer species you encounter, because these are tough environmental conditions to adapt to. Life here is thought to have changed little over millions of years. Some abyssal species include the common fangtooth, tripod fish shown (they’re hermaphroditic, meaning they have both male and female reproductive organs, which means they can produce young either with another fish or on their own!), hagfish, cusk eels, grenadiers, and viperfish. In some places, you can find deep sea-corals, which don’t need sunlight to survive. Deep-sea creatures must be able to tolerate intense pressure (from the weight of the water above), total darkness, and near freezing temperatures. That’s not to say that animals living closer to the surface have an easy life; they face a greater risk from predators and from changes in environmental conditions. How low can you go? The hadalpelagic zone The deepest zone in the ocean is the hadalpelagic zone, (also called the trenches) which is anything deeper than 6,000 meters (about 20,000 feet) below the surface, such as in the deep ocean trenches. This realm is named after Hades, the Greek god of the underworld. We don’t know much about this zone, because it’s hard to get to and requires super specialized technology to cope with the immense pressure. Life becomes very limited in this zone. You can find giant, single-celled xenophyophores, deep sea microbial mats, amphipods, sea cucumbers, jellyfish, and other invertebrates such as tube worms, decapods, bivalves, and sea-anemones. Species of snailfish, cusk eels, and eelpouts can also be found in this region but are limited to relatively shallow areas, and usually closer to the seafloor. And even though it is really hard for people to venture this far down, our trash manages to find a way — namely, our plastic. Yup, even here in the deepest part of the ocean, recent expeditions found a plastic bag at one of the deepest points of the Mariana trench, nearly 11 kilometers (about 7 miles) down. Ugh.

Article / Updated 04-19-2021

A reef is a ridge of rock, sand, or coral near the surface of the water, but because this article is about ecosystems, we’re going to focus on reefs that are teaming with life—coral reefs and oyster reefs. Coral and oysters, respectively, are responsible for building the foundation on which these living reefs grow. Coral reefs While coral reefs may seem like lifeless rocks, they are actually incredibly complex ecosystems created by a marine invertebrate called a coral polyp. Classified as cnidarians (pronounced ny-dare-ee-uhns), they’re related to jellyfish and sea anemones. Over 2,500 species of coral exist, and they can be broken down into two groups: hard (rigid) and soft (flexible). The hard ones (such as brain coral and elkhorn coral) are referred to as “the reef builders” because they create the hard material that forms the basis for the ecosystem. The soft ones (such as sea fingers and sea whips) hang out in and around reefs. Coral reefs exist in relatively shallow water (usually no deeper than around 100 feet) because the algae (zooxanthellae) that live symbiotically inside the coral polyps, providing them with essential nutrients, requires sunlight. Coral polyps (see the following figure) build large reefs through the process of creating small homes for themselves out of calcium carbonate that are tightly packed next to other coral polyps that do the same thing. Reefs grow when subsequent generations of coral polyps stack their homes on top of their deceased predecessor adding height and volume to the structure. As they create more and more homes, they end up with a massive system similar to a human apartment complex which is formally known as a “colony.” All the polyps within a colony are genetically identical, and the colony as a whole is considered a single living organism. As more and more colonies are built (by the same or different species of hard coral), a coral reef is formed. Depending on its size, a healthy reef could have hundreds of thousands to billions of diverse coral polyps living together in close quarters, just like a large human city. Different colonies even engage in turf wars with the polyps of one colony stinging those of the other colony. (Can’t we all just get along?) So, what may look like a bunch of rocks, is actually a living ecosystem with a dazzling array of colors and shapes that would make Picasso cry. But that’s not all. In the process of building homes for themselves, coral polyps lay the foundation for rich ecosystems that provide food and shelter for highly diverse populations of other marine organisms, including thousands of species of fish, invertebrates, plants, algae, sea turtles, birds, and marine mammals. The largest coral reef on the planet is the Great Barrier reef, and it can be seen from space. Coral reefs are some of the most stunning places on the planet (see the following figure). Soft corals also build their own homes but they do so out of spongy material, so the homes are more flexible and fragile. (I know, this is sounding like the story of the three little pigs, right?) While soft corals don’t qualify as reef builders, they’re a beautiful part of some reef systems. The value of coral reefs extends far beyond their beauty and the fact that they provide food and shelter for a rich community of marine life. They’re also the first line of defense against waves and storms that threaten to batter the coasts. The World Wildlife Fund and the Smithsonian Institute estimate the commercial value of coral reefs worldwide at a minimum of $1 trillion per year, $300 to $400 billion of which is attributed to food, tourism, fisheries, and medicines. Coral is actually white because it’s made from calcium carbonate, which is essentially limestone. In fact, most limestone is actually ancient coral reefs, and if you look closely at limestone buildings, sometimes you can see the outline of the coral polyps and ancient shells that lived on the reef. What gives living corals color are the zooxanthellae (algae) that live in a symbiotic (mutually beneficial) relationship with the coral polyp. The zooxanthellae, which live inside the coral polyps, capture energy from the sun and turn it into food (like a plant), which is shared with the coral polyps. In exchange, the coral provides the zooxanthellae with a place to live and chemical compounds needed for photosynthesis. Corals come in a variety of shapes, which vary mostly by the species that build the colonies, but their shape is also influenced by the wave action where they live. In more turbulent waters, they tend to grow as mounds or flattened shapes, like tables, whereas in calmer seas they form more intricate branching structures. Coral reefs at risk Coral reefs are disappearing at a terrifying rate. Up to 40 percent of the world’s coral has died in the last few decades, including half of Australia’s Great Barrier Reef. How could this happen? Well, coral may be hard as a rock, but the coral polyps that build it are sensitive to changes in their habitat. Two main factors threaten the coral reefs—heat and pollution. First consider the impact of heat. As the temperature of the ocean rises (due to global warming), in many places it frequently passes the threshold tolerable for corals to live. When that happens—the zooxanthellae living inside the polyps begin to produce toxins, or they become parasitic, so the coral essentially kicks them out of the house. And without the zooxanthellae, the polyps starve. The second threat is pollution in the form of excess nutrients in runoff, chemicals in plastics and sunscreens, and other sources, which can kill the zooxanthellae, the coral, or both. Because zooxanthellae are the source of the coral’s color, when they’re gone, the coral turns white, a phenomenon called coral bleaching (see the following figure). Even if the coral polyps are still alive, all you see is the white because polyps are basically transparent without their zooxanthellae. Unfortunately, even if the polyps survive, they begin to slowly starve to death. So, while coral bleaching isn’t necessarily a death warrant, it’s a serious warning sign that the coral is stressed and at increased risk of death. If water conditions don’t return to normal relatively quickly, the polyps will die, and all that beauty, mystery, wealth and diversity dies with them. Oyster reefs Not to be outdone by the coral polyps, oysters create their own colonies and, in the process, create rich ecosystems that provide food and shelter for a rich marine community, not as diverse as coral mind you, but still pretty diverse. So, if hard corals build coral reefs, how do oysters go about building oyster reefs? Well, it all starts with baby oysters (okay, technically oyster larvae that develop into juveniles called spat), which, at this stage of their lifecycle are free-floating. At the mercy of currents and tides, they float around aimlessly in salty or brackish water until they find something to latch onto — a rock, a shell, even another oyster. After taking hold, they grow and release more larvae, some of which settle down nearby, and the cycle continues until a structure is formed worthy of being called a reef. These reefs are wonderful places for other benthic marine animals to latch onto, including mussels, barnacles, and sea anemones. Collectively, all these animals and the creatures attracted to the structures they create form an abundant food source for many species of fish and other marine animals, not to mention humans who love slurping down oysters on the half-shell. Along with food, oyster reefs provide a nursery ground for many creatures, including shrimp, herring, striped bass, flounder, blue crabs, and more. Oysters and other bivalves (clams and mussels) are incredible little water filtration machines. A single oyster can filter two gallons of water every hour! Just search online for “oyster filtration video”—it’s mind blowing. Oyster reefs are important for water quality, fish stocks, human food, and (like coral reefs) they protect the coastlines from waves, tides, and storms.

Article / Updated 04-19-2021

Shoreline (littoral) ecosystems are those that follow the coastlines, where land and water meet. Think of them as the transition from land to sea. They’re generally wet or at least damp most of the time, and salty, but water and salt content vary based on how far inland you go and on the terrain and climate of the area. In some areas, you may find an entire ecosystem living in and around a body of water not much larger than a puddle, whereas other shoreline ecosystems are beneath the ocean’s surface most, if not all, the time. In this article, we lead you on a meandering journey down the shoreline to visit a variety of ecosystems and meet the characteristic and fascinating residents of each. Digging life in the sand What a great feeling it is to spread your beach blanket out on the sand and relax the afternoon away in peace and solitude. Well, not to ruin it for you, but you’re not alone. Even though you may not see any people milling about, you’re actually lying on a very crowded beach teaming with life, and we’re not just talking about those seagulls trying to steal your lunch. Above and below the surface of the sand are a variety of lifeforms, most of which are too tiny for you to see. But don’t let their tinyness fool you; among these lifeforms are some really tough cookies. After all, beach living is a hard-knock life. Imagine being small and living on a beach. You go from being underwater, wet and salty one moment, to being exposed, dry, and hot the next. If you’re small enough, you have to deal with the tight squeeze between sand particles, and if you’re large enough, those same particles are constantly scraping against you and getting into your eyes and nose and, well, everywhere else. To top it all off, unless you’re lucky enough to live in a bay or other protected area, you’re tossed around all day by unrelenting waves. Living here are tiny microbes too small to see, along with algae, plankton, sand dollars, crabs, and snails. Big animals like the sandy shoreline, too, including fish, rays, and sharks, which scour the shallow waters for food; turtles (for nesting); birds (for feeding); and pinnipeds (for napping). One notable inhabitant that may have you grabbing your blanket and heading back to the motel is the innkeeper worm (shown). They generally hang out below ground (thank god for small favors) but occasionally wash up on beaches by the thousands when they get spooked out of their burrows. Living life on the rocks To live on a rocky seashore, you have three options: find a tide pool to hang out in, wedge yourself in a nook or cranny, or hang on for dear life. (A tide pool is a puddle in a rocky depression that fills with sea water at high tide, remains relatively full at low tide, and is refilled at high tide with fresh sea water and nutrients.) The tide pool option is the cushiest. It’s sort of like having your own apartment with a bunch of diverse and colorful roommates — mussels, snails, starfish, barnacles, anemones, urchins, limpets, crustaceans, seaweed, and even small fish and octopus. Nooks and crannies are a little more exposed to waves and wind, so they tend to favor animals that can either hold on or retreat deeper into holes when the going gets rough, such as crabs, sea snails, chitons (pronounced “kite-ins”), and sometimes starfish. The harshest real estate on the rocky shore is right where the water meets the land. All these residents can do is hold on for dear life as they are frequently battered along these rocky high-energy coastlines. (High-energy refers to frequent large waves crashing against the shore.) Two of the toughest hangers-on are barnacles and chitons. Barnacles are sessile (immobile) crustaceans that commonly cement themselves to rocks, piers, bridges, and boat hulls. Imagine stationary crabs in cone-shaped shells they grow themselves (see the following figure). They generally grow in colonies that look like rough concrete, but if you look closer, you can see tiny animals reaching out to grab any food that happens to float past. Chitons are mollusks that look like turtles without heads, legs, or tails (shown). They can lie flat to wedge themselves between rocks or curl up like armadillos. You can tell a chiton when you see one by the eight overlapping armored plates on its back. Rocky shores are also home to larger animals that spend a significant amount of time out of the water, including penguins, a wide variety of sea birds, and pinnipeds including seals, sea lions, and elephant seals. Mixing it up in the estuaries Estuaries are partially enclosed areas along the coastline where fresh water from rivers and streams flow into the ocean. Here, fresh water and saltwater mix, causing brackish water (not too salty, not too fresh, but somewhere in the middle). The salinity of the water changes throughout the day and the seasons depending on the tide, air temperature, rainfall, and other conditions. If that’s not enough to mix you up, depending on the estuary, it can include a variety of habitats such as coral reefs, oyster reefs, rocky shores, mudflats, salt marshes, and mangroves. For example, Chesapeake Bay has three different habitats such as oyster reefs: home to oysters (duh!), mud crabs, and small fish; seagrass, where sea horses, blue crabs, and fish hang out; and open water, where you can find sea turtles, rays, and more fish. Estuaries are also home to the largest reptile in the world — the estuarine crocodile, which can grow up to 21 feet long. Crikey! That’s one huge reptile with a nasty temper, to boot, but don’t worry — they live only in the tropical estuaries of Australia and Southeast Asia. Estuaries are in constant decline due to coastal development, dredging, overfishing, and pollution. Muddling through the mudflats A mudflat (aka tidal flat) is just what it sounds like—a flat, barren expanse covered in mud that usually forms where river meets sea. The river carries particles of mud downstream and dumps them in the ocean. When the tide comes in, it slows the flow of the river allowing the particles to settle. Typically, wave action in these areas is minimal, so the fine particles aren’t washed out to sea. Mudflats are covered with water at high tide and uncovered at low tide, at which time they can become some of the muckiest, most foul-smelling places on the planet at least to humans. The stench comes from the swamp gases, methane (CH4) and hydrogen sulfide (H2S), produced by bacteria that live in the mud and help break down organic matter to make it more digestible. These bacteria, along with algae living on the surface and detritus (decomposing plants, animals, and other organic matter), provide a rich source of food to anchor the food web. Protozoa and nematode worms feed on the bacteria; crustaceans, mollusks, and polychaete (pronounced “poly-keet”) worms feed on the bacteria, detritus, and the nematodes; and larger animals in turn feed on them. Mudflats are also vitally important stopover areas for migrating shore birds who rely on mudflat residents such as crabs, fish, and mollusks to fuel their long journeys. Looking at a mudflat, you might conclude that it’s a smelly wasteland, and you wouldn’t be the first. People have destroyed many of these valuable ecosystems by filling them in and building on top of them in the name of coastal development. But that’s a big mistake because, in addition to serving as a huge source of food to coastal ecosystems, mudflats also help prevent coastal erosion. They’re also wonderful places to hike and watch birds. However, if you decide to hike a mudflat (an activity cleverly called “mudflat hiking”), be sure you go with a guide who knows the tides well. Muck, especially sandy muck, is like quicksand. If you don’t know what you’re doing, you may find yourself up to your chest in muck with the high tide rushing in. Settling down in salt marshes Salt marshes are like mud flats but with vegetation. They usually form after enough mud and peat (decomposing plant matter) has accumulated to raise the ground level to a point at which it’s high enough to support the growth of saltwater grasses and other plants that have adapted to living in shallow saltwater. Salt marshes are flooded and drained daily or at least occasionally by the overflow of ocean water, which ensures a steady supply of salt. Like mudflats, salt marshes are home to snails, mussels, worms, and crabs, but they also attract fish and shrimp looking for food or a place to lay their eggs amidst the relative safety of the plants that offer plenty of nooks and crannies to hide in. Ducks, geese, wading birds and many migratory bird species also come to feed on the abundant vegetation, seafood, and insects. Mammals are attracted to salt marshes, too, with mice, rats, and raccoons coming to feed on the bounty; even the occasional coyote has been known to frequent salt marshes for the fine dining experience. Clearly, salt marshes are very important to an enormous range of species . . . including humans. They provide essential food, refuge, and/or nursery habitat for many fisheries species that are vital to many coastal economies, including shrimp, blue crab, and many fish. In addition, they filter runoff water and help fight erosion. Salt marshes can be found all over the world. In the United States, half of all the salt marshes are located along the Gulf Coast of Texas, Louisiana, Alabama, Mississippi, and Florida, but thanks to oil and gas development they are disappearing fast. Meandering through the mangroves Mangroves are a group of tropical and subtropical trees and shrubs that live in the intertidal zone. They range in size from small shrubs to huge 40-foot-tall trees and are adapted to living in saltwater. Some species get rid of excess salt thru their leaves while others have special pores that keep much of the salt from entering in the first place. So, mangrove trees are cool, but what have they done for us lately? Well . . . a lot, including the following: Provide a habitat for algae, insects, mollusks, crustaceans, fish, sharks, birds, dolphins, manatees, turtles, lizards, crocodiles, alligators, snakes, frogs, small mammals, a few marine mammals, and more insects than you can probably imagine. Serve as a nursery where many fish and other sea creatures lay eggs, give birth, and protect and feed their young. Mangrove forests are directly or indirectly responsible for a considerable percentage of the global fish catch. Protect the coastlines and coastal communities from storm surges, hurricanes, typhoons, waves, and floods. (Every 330 feet of mangrove forest can reduce wave height by up to 66 percent.) Filter the water, improving clarity and quality. Store carbon, which mitigates global warming. One acre of mangrove alone can sequester 1,450 pounds of carbon a year, which is the amount of carbon produced by driving your car across the United States three times. That’s also more carbon than can be stored by an acre of any inland forest. (See Chapter 21 for details.) Contribute to the world economy. Worldwide, mangroves contribute about $1.6 billion each year to local economies. Mangroves not only protect land but also create it. Mud collects around the network of roots leading to the development of shallow mudflats. Any discussion around the mangrove ecosystem is more like a tale of two ecosystems—the one below water and the one above it—as explained next. Living among the roots Some mangroves have roots that reach from above the surface of the ocean down into the substrate below. This enables them to survive the ups and downs of the tides, but it also creates a tangle of roots that makes an ideal habitat for small ocean creatures, including the following: Invertebrates (animals without backbones): Snails, barnacles, bryozoans, tunicates, mollusks, sponges, polychaete worms, isopods, amphipods, shrimps, crabs, and jellyfish all live in or near the network of roots. Fish: A wide variety of fish live inside or adjacent to the root system, many of them, such as sharks, in the juvenile phases of life where they’re safe from bigger fish that can’t get in between the roots. Fish types vary according to water temperature, salinity, turbidity (cloudiness), and other characteristics of the water. In addition, salinity can change with seasons, drawing more or fewer freshwater species that can tolerate some salinity. Marine mammals: Farther out from shore, you can find some marine mammals, including bottlenose dolphins, manatees, and dugongs. Dolphins are typically in search of fish, whereas manatees dine on the vegetation. Keeping your head above water Above the waterline, mangroves support an even greater diversity of creatures, most of which are terrestrial or amphibious, including the following: Reptiles: Crocodiles, alligators, various snakes and lizards, and land turtles and (farther offshore) sea turtles. Also, some freshwater turtles nearer to the headwaters may frequent the mangroves. Amphibians: Amphibians aren’t generally drawn to mangroves because of the salinity of the water, but you may find some tree frogs and toads. Birds: Many species of birds live in the mangroves or feed there, including egrets, heron, spoonbills, ducks, grebes, loons, cormorants, falcons, eagles, owls, vultures, and more. Mammals: Mammals that frequent the mangrove forests include panthers, raccoons, skunks, mink, river otters, bobcats, possum, rabbits, rats, and even deer.

Article / Updated 04-19-2021

The ocean is our favorite hangout, colorfully decorated and home to some of the most fascinating characters, some of which are potentially dangerous. To stay safe, you need to watch your step, keep your hands to yourself, respect the residents, and steer clear of some of the more dangerous denizens. In this article, we introduce you to nine sea creatures (in no particular order) to appreciate from a distance and the deadliest creature on land or sea. Our goal is to inspire awe and respect, not fear. Every creature mentioned has adapted to survive and thrive in the ocean ecosystem. Some are large and fast with powerful jaws and big teeth, others use camouflage to their advantage, some are really smart, some carry toxins, and others pack a weapon, but we love them all and hope you do, too. Note: We want to give a special shout out to our dear friend and a person with a super cool job, Prof Jamie Seymour, PhD, at James Cook University. As a leading toxicologist/venomologist, he works with many of these deadly animals every day. Talk about brave. Saltwater Crocodiles Saltwater crocs can grow in excess of 20 feet and 2,000 pounds They have big teeth, powerful jaws, can run about 15 miles per hour (in short sprints) and swim about 20 miles an hour. You may be able to outrun one, but you can’t outswim one. Three characteristics make them particularly deadly. First, they’re aggressive. You don’t need to poke ‘em with a stick to make ‘em mad. All you need to do is invade their personal space. Second, they ambush their prey. They hang out very still at the water’s edge, sometimes half buried, until an unsuspecting monkey, boar, water buffalo, or other animal drops by for a drink—then bam! They clamp down and won’t let go. Third, immediately after clamping down, they do a death roll to drown and dismember the body, so if the initial attack doesn’t kill you, you’ll soon wish it would have. Saltwater crocs have even been known to attack and eat sharks. We’re guessing the winner would come down to size and to who surprised whom. Fugu Fish Fugu fish, a type of pufferfish or blowfish, are considered by some to be a delicacy. However, if not prepared properly, this fish could be the last one you ever eat. When threatened, the pufferfish can blow itself up to several times its normal size, and some are covered with spines. If the predator doesn’t take the hint and ends up eating the pufferfish, it’s in for a rude surprise—the pufferfish contains a toxin that makes them taste horrible and is potentially deadly. In fact, this cute little puff of joy carries enough toxin to kill up to 30 adult humans, and it has no known antidote. Eating fugu is like playing Russian Roulette with your dinner. Tetrodotoxin, stored in the liver, ovaries, and other parts of this fish, may be more toxic than cyanide. A small dose of tetrodotoxin could result in numbness in your mouth, vomiting, paralysis and possibly death. We recommend crossing it off your menu. The pufferfish is poisonous, not venomous. What’s the difference? A poisonous animal is toxic but doesn’t actively deliver the toxin — you have to touch it or eat it. In contrast, venom is delivered intentionally; for example, through a bite or sting. Some animals, such as a spitting cobra, are toxungen, meaning they spit, spray, or fling their toxins. Killer Whales Their name says it all. Killer whales (orcas) are one of the few mammals that kill for fun. In fact, they hunt in packs and teach their calves how to hunt from an early age. They’re also big, powerful, and smart, making them one of the most formidable ocean predators. In a meet up between a killer whale and a great white shark, the killer whale would likely prevail. They’ve even developed a special technique for dealing with sharks—biting the shark and turning it on its back to put the shark in a coma-like state called tonic immobility. Told you they were smart. While orcas in captivity have fatally wounded people (another reason to #EmptyTheTanks), none has ever been reported to have killed a human in the wild. Blue-Ringed Octopus Beautiful and deadly, the blue-ringed octopus is named after the vibrant blue circles it shows when feeling threatened. Though docile, their bite contains the powerful neurotoxin called tetrodotoxin (the same toxin carried by the fugu pufferfish). The octopus uses the venom to immobilize its prey for an easier meal that doesn’t wiggle around. Fortunately for the octopus eating this tainted meal, it’s immune to its own venom, but you most certainly are not! Sea Snake While snake enthusiasts can’t agree on the most venomous snake, they do agree that sea snakes are super venomous But, venomous and deadly are two different things. Sea snakes are very docile, and they don’t have huge front fangs like those of cobras, so they’re not likely to bite you. Even if they do, they may not deliver enough venom to kill you. However, if you were to get a good dose of it, good luck. It’s highly concentrated. Stone Fish The stone fish holds the title for most venomous fish in the world, but you may not even notice them, because they look like rocks. Well, you may not notice until you step on one. Then, holy fugu fish, do they ever pack a lethal punch! The first sign of trouble is that your foot becomes impaled on the spikes of their dorsal fins (exceedingly painful). Then, the toxin enters the bloodstream causing swelling around the wound, difficulty breathing, irregular or no heartbeat, nausea, vomiting, delirium, and even death. The good news is that as long as you don’t step on one, or accidently grab it, you have little to fear. Sharks (But Not All of Them) Many sharks are apex predators that play a key role in maintaining a healthy ocean. These predators are big, strong, and fast and are equipped with big, sharp teeth and strong jaws. But some sharks pose a greater threat than others. Some of the deadliest (to humans) sharks include the following: Great white shark Tiger shark Bull shark Oceanic whitetip shark Blue shark Shortfin mako shark However, the vast majority of sharks are relatively harmless to humans, including the following: Whale shark Nurse shark (as long as it’s not harassed) Basking shark Leopard shark Angel shark Bamboo shark Even predatory sharks pose a nearly negligible risk to humans. Cone Snails Yep, this beautiful little snail is a vicious predator. Experts hypothesize that a single cone snail contains enough venom to kill 700 adult humans. Like other snails, the cone snail is slow, so it uses a harpoon-like tooth to inject venom into its prey, quickly immobilizing the prey so the snail can eat it. If you’re on the receiving end of one of the snail’s venom-tipped harpoons, head to the hospital; death can occur within one to five hours in severe cases. While there is no anti-venom, on the bright side, scientists have used the venom to create better, non-addictive painkillers and insulin. Box Jellyfish While people tend to fear sharks the most, if they’re going to be afraid of anything in the ocean, it should be the box jellyfish. They’re translucent, so you can barely see them in the water. They’re much better swimmers than most jellies. They have lots of eyes (24 to be precise). They deliver their venom on contact, and a sting from the most venomous of the group can result in paralysis, cardiac arrest, or even death in a matter of two to five minutes. Yikes. Humans Even with all these deadly creatures in the sea, from tiny cone snails to giant predators much larger than people, humans are the most dangerous creature out there. Over the past 40 years, thanks to humans, 50 percent of the biodiversity on earth has disappeared and over 1,000 species go extinct each year. Every year, humans are responsible for killing hundreds of millions of sharks; billions of pounds of fishing bycatch; and more than 300,000 small whales, dolphins, and porpoises (due to fishing line entanglement), not to mention the fact that every year humans murder about 450,000 other humans. Man, we really are the deadliest species on the planet.