50 Fun Facts About Marine Biology

Which metal, carried in the protein hemocyanin, turns the blood of squid and lobsters blue instead of red?

Copper does the job that iron does in human blood, binding oxygen and turning blue as it does so. The same pigment runs through snails, spiders and scorpions.

Which microscopic drifting organisms make about half of Earth's oxygen by photosynthesis in the sunlit sea?

Phytoplankton manage it while making up only about 1% of the planet's plant biomass. They also sit at the base of nearly every food chain in the sea.

In which fish does the male carry the eggs in a brood pouch until the young are born?

Seahorse fathers receive up to 1,500 eggs from the female and carry them for 9 to 45 days. The young emerge fully formed but very small.

Which marine mammal has no blubber and relies instead on the densest fur of any animal to stay warm?

Sea otter fur packs up to 150,000 hairs into each square centimetre. The animal grooms constantly, because the coat only keeps water out while it stays clean.

Which bright reef fish rasps algae off coral rock and excretes the remains as sand?

Parrotfish digest the edible part and pass the rest as sand, which helps to build beaches and small islands.

Which large land animals are the closest living relatives of manatees and dugongs, despite the nickname sea cows?

Elephants share the kinship with the small, furry hyraxes. Manatees even replace their molars the same way, with new teeth moving forward from the back of the jaw like a conveyor belt.

Which Arctic whale grows a spiral tusk, up to three metres long, that is really an overgrown canine tooth?

Narwhal males grow the tusk from the left side of the upper jaw. The scientific name, Monodon monoceros, is Greek for single-tooth, single-horn.

Which striped reef fish shelters among sea anemone tentacles and has males that turn female when the top female dies?

Clownfish live in a strict pecking order ruled by the largest fish, the breeding female. In return for shelter they clean and fan the anemone and chase off fish that would eat it.

Which sluggish Arctic fish is the longest-lived vertebrate known, with a lifespan estimated at several centuries?

Greenland shark females may not breed until they are about 150 years old. The cold-water giant also has the slowest swimming speed for its size of any fish.

Which tide-pool predator pries open clams, then pushes its own stomach out of its body to digest them in the shell?

Starfish need a gap of only a fraction of a millimetre between the two shells to slip the stomach in. Most can also regrow lost arms.

What is the term for light made by living organisms, such as deep-sea lanternfish and sparkling dinoflagellates?

Bioluminescence is far commoner in the deep than near shore: about 76% of the main groups of deep-sea animals in one Pacific survey could make light, against some 2.5% of coastal organisms.

What is the name for the way dolphins find prey by sending out clicks and reading the sound that bounces back?

Echolocation is the main sense of toothed whales, which can survive by it even when completely blind. The clicks pass out through a fatty organ in the forehead called the melon.

What flexible tissue, rather than bone, makes up the skeletons of sharks, rays and skates?

Cartilage gives the whole class its name: Chondrichthyes comes from the Greek words for cartilage and fish, in contrast to the bony fish, Osteichthyes.

Coral reefs are built by colonies of which tiny sac-like animals that secrete hard skeletons of calcium carbonate?

Polyps are usually only a few millimetres across, and every one in a colony is genetically identical. Scholars argued for millennia over whether corals were plants or animals.

Which gas, absorbed from the air by seawater, is making the oceans more acidic and threatening shell-building animals?

Carbon dioxide from human activity lowered the average pH of the sea surface from about 8.15 to 8.05 between 1950 and 2020. Corals and mollusks suffer because they build with calcium carbonate.

In sea turtles, which condition of the sand around a buried nest decides whether hatchlings become male or female?

Temperature sets the sex partway through incubation: cooler nests hatch mostly males and hotter nests mostly females, so warming beaches may tip whole populations female.

Which ocean giant, the largest animal known to have ever existed, feeds almost entirely on tiny krill?

Blue whale hearts are the largest of any animal: one from a stranded North Atlantic individual weighed 180 kg. The animal itself can reach about 30 metres and 190 tonnes.

What comb-like plates of keratin do humpback and right whales use to strain small prey from mouthfuls of seawater?

Baleen is made of the same substance as human fingernails and hair. The whale gulps water, then pushes it out through the plates, which hold the food back.

Which brown seaweed forms towering underwater forests and can grow about half a metre in a single day?

Giant kelp can grow more than 45 metres long, anchored to the seabed by a root-like holdfast and lifted toward the light by gas-filled bladders at the base of its blades.

Which salt-tolerant trees fringe tropical coasts, standing above the tide on tangled, stilt-like prop roots?

Mangroves filter out salt and take in air through pores in their bark, and some drop ready-grown seedlings that can float for up to a year before taking root.

Corals, sea anemones and box jellies all belong to which phylum, named after the Greek word for nettle?

Cnidaria arm their tentacles with cnidocytes, stinging cells that fire a coiled thread to envenom and capture prey. The phylum holds more than 11,000 species.

Sea urchins, sand dollars and brittle stars belong to which phylum, named from the Greek for hedgehog skin?

Echinodermata are built on a five-part radial plan as adults, yet their free-swimming larvae are two-sided like most other animals.

Which class of mollusks, whose name is Greek for head-feet, includes squid, cuttlefish and the nautilus?

Cephalopoda are sometimes called inkfish by fishers, after their shared trick of squirting ink. The class includes the colossal squid, the heaviest living invertebrate.

Which simple animals, classed as phylum Porifera, pump water through bodies full of pores and have no nervous system?

Sponges with soft, fibrous skeletons were used for thousands of years as padding and cleaning tools, which is where the bath sponge gets its name.

In the great white shark's scientific name, Carcharodon carcharias, which taxonomic rank does the first word give?

Genus comes first, and the second word marks the species. The great white is the sole living species of Carcharodon; Linnaeus had first filed it under Squalus with every other shark.

Seals, sea lions and the walrus make up which group of marine mammals, named from the Latin for fin and foot?

Pinnipeds include the walrus, the only surviving member of its family, alongside the eared seals and the earless true seals.

Which land mammal is the closest living relative of whales and dolphins, a kinship first shown by blood proteins?

Hippopotamus ancestors and early whales shared a semiaquatic forebear and parted ways about 55 million years ago, which is why whales now sit among the even-toed hoofed mammals.

Which apex predator, a toothed whale, is the largest member of the oceanic dolphin family?

Orca groups pass their own calls and hunting techniques down the generations, behaviour that scientists regard as a form of animal culture.

Which helmet-shaped beach animal, little changed in 250 million years, is closer kin to spiders than to any crustacean?

Horseshoe crab blood contains a substance that reacts to bacterial toxins, so the animals are caught and bled to make a test for contamination.

Which animals, cemented head-down to rocks and ship hulls, did Charles Darwin study for eight years?

Barnacles so filled Darwin's days at home that his young son, visiting a friend, asked where that boy's father did his. Darwin published the results as a series of monographs.

Which process lets bacteria at deep-sea hydrothermal vents make food from hydrogen sulfide instead of sunlight?

Chemosynthesis also feeds whole communities at cold seeps and on sunken whale carcasses. Giant tube worms house the bacteria inside their own bodies and live on the sugars they make.

What are the microscopic algae called that live inside coral tissue and supply up to 90% of a coral's energy needs?

Zooxanthellae also give many corals their colour, so a coral that loses them turns white, the process known as bleaching.

Which form of camouflage gives many sharks, dolphins and fish a dark back and a pale belly?

Countershading works because light from above brightens an animal's back and shadows its belly, and the colouring cancels that out. The artist Abbott Thayer described it in 1909.

What name did explorer William Beebe coin for the steady shower of organic debris sinking into the deep ocean?

Marine snow clumps can grow to several centimetres across and drift for weeks before reaching the seabed, feeding deep-sea animals that sunlight never reaches.

Which ocean layer, nicknamed the twilight zone, lies between about 200 and 1,000 metres below the surface?

Mesopelagic comes from the Greek for middle: the layer begins where only 1% of surface light remains and ends where none does. Many of its animals climb toward the surface and back each day.

Which ecological term did Robert Paine coin after studying how one predator shapes life on Washington's rocky shores?

Keystone species take their name from the stone at the top of an arch: it bears the least pressure of any, yet the arch collapses without it.

In which deep-sea fish does the tiny male attach to the far larger female, sometimes fusing with her body for life?

Anglerfish are named for the way they hunt: a modified fin ray dangles in front of the mouth as a lure, in many species tipped with a glowing bulb.

Which sense organ running along a fish's flank detects movement, vibration and pressure changes in the water?

Lateral line signals help a school of fish hold formation and turn together, each fish sensing its neighbours; the organ also helps in hunting and finding the way.

Which lobe-finned fish, thought extinct for 66 million years, turned up alive in a catch off South Africa in 1938?

Coelacanth bodies have kept much the same plan for about 400 million years. A second living species was found off Indonesia in the late 1990s.

Which sea turtle, the largest of all living turtles, is the heaviest reptile on Earth apart from the big crocodilians?

Leatherback turtles are the only sea turtles without a bony shell: the back is covered in oily flesh and flexible skin instead. They can reach 2.7 metres and 500 kg.

Which French naval officer co-invented the Aqua-Lung and filmed the undersea world from his ship Calypso?

Jacques Cousteau leased Calypso for a symbolic one franc a year and refitted it as a mobile laboratory for diving and filming.

Which American author won a National Book Award for The Sea Around Us, the bestselling middle book of her sea trilogy?

Rachel Carson gained financial security from the book and went on to write Silent Spring, which brought environmental concerns to an unprecedented share of the American people.

Which oceanographer, sometimes called Her Deepness, was the first woman to serve as chief scientist of NOAA?

Sylvia Earle also led the first all-female team of aquanauts in the Tektite II undersea habitat, and later walked the seabed off Oahu, untethered, in a JIM diving suit.

Which marine scientist, known as the Shark Lady, discovered that the Moses sole gives off a natural shark repellent?

Eugenie Clark worked from a laboratory that admirers built for her in Florida, now the Mote Marine Laboratory, and used her fame to promote marine conservation.

Which British warship's 1870s voyage around the world found about 4,700 new marine species and founded oceanography?

HMS Challenger was fitted out with separate laboratories for natural history and chemistry, and its crew discovered the Mariana Trench in 1875.

Which research submersible took scientists to the first known hydrothermal vents in 1977 and later to the Titanic wreck?

Alvin is named after Allyn Vine, the scientist who championed the craft, and has made more than 5,200 dives since it was commissioned in 1964.

Which Greek philosopher's observations of sea life around the island of Lesbos mark the beginnings of marine biology?

Aristotle spent about two years on Lesbos studying a lagoon at the island's centre, and correctly reported that the young of a dogfish grow inside the mother's body.

Which marine biologist, author of Between Pacific Tides, inspired the character Doc in Steinbeck's Cannery Row?

Ed Ricketts was a friend and mentor of John Steinbeck, and the pair co-wrote Sea of Cortez in 1941.

Which term describes fish, such as salmon, that live at sea as adults but migrate into fresh water to spawn?

Anadromous comes from the Greek for up and course. Freshwater eels do the reverse, living in rivers and heading down to the sea to breed.

Which vividly coloured sea slugs take their name from the Latin and Greek words for naked gills?

Nudibranchs earn nicknames such as marigold, dancer and dragon for their extraordinary colours, and many breathe through a plume of bare gills on the back.