Ocean Life: Species, Biodiversity, Oldest and Most Numerous

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Marine worms painting made in late 19th century

In “The Extreme Life of the Sea”, Stephen and Anthony Palumbi wrote: There are about as many bacteria in a liter of water of seawater as there are people in India — over a billion. In April 2010, scientists at Woods Hole involved with 10-year Census of Marine Life, estimated there was a mind-mind-boggling nonillion, or 1,000,000,000,000,000,000,000,000,000,000 (1 followed by 30 zero) individual microbial cells in the oceans, weighing as much as 240 billion African elephants and making up 50 percent to 90 percent of the oceans’ biomass. Among their findings were a bacteria colony — comprised of whitish mats — the size of Greece on the floor of the Pacific Ocean off Chile and Peru.

Under the surface of the ocean, light is greatly altered. By just 200 meters below the surface, photosynthesis becomes impossible. At 1,000 meters down, sunlight disappears completely.

Trilobites first appeared about 500 million years, They “were a dominant part of life in the sea for 200 million years, 100 times longer than man has existed.”

Out of the millions of insects species only five can live in the open ocean — five species of water strider. The only reptiles that can do so are salt water crocodiles, sea turtles, sea snakes, Galapagos marine iguanas and some monitor lizards that occasionally take to saltwater. There are lots of mammals — whales, dolphins, seals, walruses and dugongs — that live in the sea..

Censuses of marine species are taken in coastal waters and reefs by scuba divers who measures out a an area on the ocean floor and count the numbers and estimate the size of different species they observe and record the numbers with a pencil on waterproof paper. In the past scientists have traditionally relied catch numbers from fishermen to determines the health and population size of marine species.

Taxonomic Category or Rank: 1) Kingdom; 2) Division: 3) Class; 4) Order: 5) Family; 6) Genus; 7) Species

Websites: Animal Diversity Web (ADW) animaldiversity.org; NOAA site fisheries.noaa.gov; Fish Base fishbase.se; World Register of Fish Species marinespecies.org; Smithsonian Ocean ocean.si.edu; > Book: “The Extreme Life of the Sea” by Stephen and Anthony Palumbi, Princeton University Press, 2014]

How Many Species Live in the Ocean?

According to one estimate around 250,000 of the world’s 2 million known species are found in the sea. Some scientists estimate there could be as many as 10 million species out there and that number could reach 1 billion of all the existing microbes are factored in.

Given the vast size of the ocean, it is impossible to know the exact number of species that live there. Research suggests, however, that the number of species in the ocean is decreasing. The continued decline in the health of many ecosystems, coupled with rising extinction rates, are likely outpacing species’ ability to evolve to tolerate the conditions of our rapidly changing planet. It is not all bad news, though. Researchers around the world continue to study marine life and habitats to help develop new strategies to preserve vital ocean ecosystems. [Source: NOAA]

Scientists estimate that 91 percent of ocean species have yet to be classified, and that more than eighty percent of our ocean is unmapped, unobserved, and unexplored.. While these statistics may sound daunting, they have not stopped the global scientific community from striving to amass as much knowledge as possible about ocean life.

Ocean Biodiversity

The Nudibranch Glossodoris symmetricus

According to the Census of Marine Life, completed in October 2011, crabs, lobsters and other crustaceans are now believed to be the most common species in the seas of Australia and Japan, whose waters are thought of as the most varied .

The worlds seas are full of food and it is no surprise that so many forms of life are found there. A typical drops of sea water is teaming with life: bug-like copepods; long, glassy arrowworms; coiled filaments of cyanobacteria; rectangular-shaped diatoms; fish eggs and bug-eyed larva; and microscopic crabs.

Biodivesity in the sea is as high or higher than in the rain forest, with many areas, especially at depths of over 1,000 meters completely unexplored. One sampling of an area the size of a bathroom (5.4 square meters) deep in the South Atlantic Ocean turned up 700 species of copepod, a type of crustacean, 99 percent of them unknown to science.

Reefs are among the worlds most diverse habitats. They are home to about 35,000 to 60,000 species (of the world's 274,000 known marine species) and a third of the 12,000 kinds of marine fishes. They are also incredible rich in phyla, with creatures as diverse as sea lilies, sponges, crabs, eels and sea anemones all living there. Some patches of reef boast over a 100 species of fish and more than a thousand other kinds of plants and animals.

A single reef wall often contains a wider variety of life forms’species from more phyla, or major groups — than an entire continent. The rich biodiversity of the reefs is due to abundance of light warmth provided by the tropical sun and an abundance of oxygen saturated into the water by crashing waves.

Biodiversity in Different Seas

The waters of Japan and Australia are home to around 33,000 different life forms that have been elevated to the category of "species." The waters of China, the Mediterranean Sea and the Gulf of Mexico are also in the top five most biologically diverse marine regions, according to a preliminary census in the public opening of data in the Public Library of Science (PLoS ONE).

The relatively isolated waters of Australia, New Zealand, Antarctica and South Africa have the largest number of endemic species, or which are unique to that area. By contrast, the Mediterranean has more "exotic" creatures: with more than 600 species, many of which came from other places.

Pedro Martinez Arbizu, from the German Centre for Marine Biodiversity Research, was astonished to find that a tiny creature — Ceratonotus steiningeri — also was within the cataloging he had made earlier 13,000 km away in the central Pacific. There was that critter again. Same shrimpy creature, different ocean. “We were really very, very surprised about that,” Arbizu said. “We think this species has a very broad distribution area.”

20110307-NOAA reef sponge 2584.jpg
reef sponge
The census also describes a species of strange large squid that was only recently found in waters more than 900 meters deep. The 7-meter-long squid has large fins with arms and tentacles that have elbow-like bends. Scientists had seen it in larvae form before, but not in its full-blown glory until it was filmed at depth.

Ocean Environments

The Arctic and northern seas have traditionally been defined as a “benthic ecosystems,” where there are relatively few fish but many bottom-dwelling creatures such as crustaceans, mollusks and marines worms. These creatures in turn food for animals such as walruses, seals and some whales.

The midwater region, located at underwater depths of more than one kilometer, is far from the ocean surface and much of the the sea floor. Forms of life found here are supported almost entirely by “marine snow,” organic debris that drifts down from near the surface. Encompassing more than a quarter billion cubic miles, it is the world’s largest habitat, and believed to be home more than a million undescribed species and more biomass than any other system. Creatures found here include angler fish; 120-foot-long colonies of gelatinous creatures; and vampire squids that have lights and spikes on the tips of their arms and posses the ability to squirt clouds ob glowing liquid.

Deep sea vents are the hottest environment known to sustain life. Archeea, primitive unicellular microbes, thrive in mineral chimneys known as black smokers in temperature sup to 250̊C. Archeea are believed to be similar to the first forms of life found in earth. Deep sea vents, over two kilometers deep, are home to six-foot-long tube worms and variety of crustaceans and mollusk. Life here is produced without sunlight or photosynthesis.

Deep-sea, cold water coral make up two thirds of all known corals and are among the oldest organism on Earth. Found as deep as three miles below the surface, and discovered only in the 1980s, they are as diverse as shallow reef corals and protect marine life from strong ocean currents. Basophilic (pressure-loving) microbes have been recovered by a Japanese submersible in the 36,000-foot-deep Mariana Trench.

Deep Scattering Layer (DSL) — the Mobile Band of Life

Eric Wagner wrote in Smithsonian magazine: the sea is alive with creatures whose behavior was first noted during World War II, when naval sonar operators observed that the seafloor had the unexpected and somewhat alarming tendency to rise toward the surface at night and sink again during the day. In 1948, marine biologists realized that this false bottom was actually a layer of biology, thick with small fish and zooplankton. Instead of the seafloor, the Navy’s depth sounders were picking up many millions of tiny swim bladders, aggregated so densely that they appeared as a solid band. The layer is composed of fish and zooplankton that spend the day between 300 and 3,000 feet deep, where almost no light can penetrate. At night, they migrate upward, sometimes to within 30 feet of the surface. The fish are well suited to life in the dim depths, with enormous, almost grotesquely large eyes and small organs, known as photophores, that produce a faint glow. [Source: Eric Wagner, Smithsonian magazine, December 2011]

The mobile band of life was named the deep scattering layer, or DSL, for the way that it scattered sound waves. In the Sea of Cortez, the fish that inhabit it, called myctophids or lanternfish, are among the jumbo squid’s preferred prey. The squid follow the fish’s daily vertical migration, spending the daylight hours between 600 and 1,200 feet and then pursuing them toward the surface at night.

Biologists assumed that the DSL creatures were at the mercy of currents, drifting haplessly, helplessly along. But Benoit-Bird and colleagues have found that even microscopic plants and animals can lead active and finicky lives. Phytoplankton, seeking out particular conditions of biochemistry and light, will form sheets that can stretch for miles but are only a few feet high. Slightly larger zooplankton take advantage of this great conveyor of food. Lanternfish likewise fight against prevailing currents to reach the feast. Things gather to eat or not be eaten — by fish, by squid, by sperm whales. What was thought to be at the whim of physics turns out to act on its own biological imperatives.

5,000-Year-Old Coral — the World’s Oldest Living Animal?

Studies show that some corals can live for up to 5,000 years, making them the longest living animals on Earth. Scientific studies of elkhorn coral (Acropora palmata) in the Caribbean and off the coast of Florida show that coral genotypes can survive longer than expected. Genotype refers to the genetic makeup of an organism. [Source: NOAA]

Scientists are now using a genetic approach to estimate the ages of corals. The method determines when a coral egg and sperm originally met to form the genome of a coral colony. The researchers then track the number of mutations that have accumulated in the genome since that time. Because mutations tend to arise at a relatively constant rate, researchers can estimate the approximate age of the coral genomes in their study.

These studies can help clarify how corals will respond to current and future environmental changes. Though corals can be resilient and live for thousands of years, elkhorn corals are listed as threatened under the U.S. Endangered Species Act. The corals have suffered recent population declines, indicating that there are limits to how much change even these resilient creatures can handle.

Sea Animal Migrations

“Just off the West Coast may be one of the greatest hot spots for open ocean predators in the world,” said Barbara Block of Stanford University’s Hopkins Marine Station, the lead author of study of about sea animal migrations along with Daniel Costa, professor of ecology and evolutionary biology at the University of California at Santa Cruz. Block told the Washington Post she was struck by how each spring the rich nutrients in the cool water along the California Current, which flows south along the West Coast of the United States, Canada and Mexico, drew an array of animals to the same place. Young bluefin tuna make their way from Japan for the area’s soup of krill, sardines, anchovies and squid, as do leatherback turtles from Indonesia and sooty shearwater birds from New Zealand. [Source: Juliet Eilperin, Washington Post , June 22, 2011]

“They have their favorite haunts, they clearly have the places they keep going back to,” Block said. “The upwelling [of nutrients] is so intense there in the springtime it really sets the table for the whales, the tuna and the sharks. They come and lunch at that table, from everywhere in the entire Pacific realm.” The California Current is “a predictably and persistently productive region” many marine creatures gravitate to over and over again, said Steven Bograd, a research oceanographer at the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center and one of the paper’s co-authors. “We’ve characterized, better than ever before, that it is a really critical area in the life history of these animals,” he said.

The scientists emphasized that the fact that many of these commutes largely take place within the exclusive economic zones of the United States, Canada and Mexico — the 200-mile stretch from shore that individual countries can govern — means that the three countries can adequately protect these areas. On the importance of conservation, Block told Natural History magazine: “It will take enormous vision to preserve this wild place. Without conservation of such ocean realms, the bluefin tunas and blue whales, whale sharks and great whites might not be there in future generations.”

California Current — the Serengeti of the Sea?

The waters of the California Current off the west coast of the United States have been compared with the Serengeti grasslands of East Africa because of the huge animal migrations that occur there. Cheryl Lyn Dybas wrote in Natural History magazine: Water temperature is key to the seasonal migrations of many North Pacific Ocean species. That’s especially true in the marine ecosystem defined by the California Current, where whales, sharks, tuna, seals, seabirds, and turtles migrate each year. Like the African savanna, says Costa, the Pacific Ocean has a “Big Five”: he compares great white sharks to lions, bluefin tuna to leopards, blue whales to African elephants, leatherback sea turtles to black rhinos, and elephant seals to Cape buffaloes. [Source: Cheryl Lyn Dybas, Natural History magazine, September-October 2012]

“Scientists see parallels between migration patterns of prey, predators, and scavengers in East Africa’s Serengeti region and movements of species in the Pacific. Mapped here are (top left and right) zebra and wildebeest, (middle left and right) nomadic lion and hyena, and (bottom) vultures. Most lion prides occupy defended territories; nomadic lions, usually single males, tend to follow migrating herds while trying to avoid detection by resident males. “The Serengeti is an ecosystem that’s synonymous with animal movements,” says ecologist Grant Hopcraft of the Frankfurt Zoological Society–Africa, headquartered in the Serengeti. “Each year more than one and a half million ungulates cross its plains.” Their seasonal migrations follow cyclic rains that lead to the growth of savanna grasses. Where grasses sprout up, ungulates such as wildebeest follow. Predators such as nomadic lions trail closely behind. (Although most lion prides occupy defended territories, nomadic lions, usually single males, tend to follow migrating herds while trying to avoid detection by resident males.) “The movements of marine species in the California Current are similar to those in the Serengeti,” says Hopcraft, “which raises the question: Why? Research at the population level suggests that it’s a changing food supply that drives animal migrations. But recent animal collaring [tracking] projects in the Serengeti show a huge amount of variation in individual species’ responses.”

There’s a lot more going on, Hopcraft believes, beneath the surface. “For the Serengeti — and the California Current — does an animal’s internal condition determine how it responds? Is it remembering previous routes and responding to the same cues? How will environmental change affect these great migrations of the land and the sea?”

Some predators spend their lives in the California Current, but others migrate long distances across the Pacific Ocean to reach the current’s abundant prey, including krill, sardines, anchovies, and squid. “Why a young bluefin tuna less than two years old wakes up in the light of the Japan Sea and decides to swim to Baja is unknown,” Block says. “But once it arrives, tagging data indicate that it lives there for years, taking advantage of the rich ‘forage’ along the coast.” Many species — including black-footed albatrosses, sooty shearwaters, bluefin tuna, and salmon sharks — migrate more than 1,200 miles from the western, central, or southern Pacific Ocean to reach the California Current’s rich food resources.

Different Species Follow the Same Migrations Routes in the Pacific

leatherback turtle
Juliet Eilperin wrote in the Washington Post, “Tagging revealed that several species — including leatherback sea turtles, black-footed albatrosses and salmon sharks — followed similar routes from the western, central or south Pacific to reach the current’s rich resources.While scientists tracked most animals for less than a year, they followed several tunas, sharks and turtles for longer: in the case of one salmon shark, well more than 3 ½ years. [Source: Juliet Eilperin, Washington Post , June 22, 2011]

Costa said the fact that these different creatures are following the same path helps account for why some of them, including leatherback turtles, get caught by fishing vessels that are targeting other species. In one instance, he noted, the same female elephant seal tagged in 1995 off the island of Ano Nuevo north of Santa Cruz “took the same exact path 11 years later” when researchers tagged her again. “It’s not genetic; it’s some sort of learned behavior,” Costa said in an interview.

Ocean temperatures In the case of sharks, Block said, researchers were able to determine that species with a common ancestor — salmon, white and mako sharks — preferred to spend time in slightly different temperatures. In Alaska, salmon sharks swim in water as cold as 42.8 degrees but can manage in temperatures as high as 53.6 degrees; great whites stick close to the California coast at 53.6 degrees but journey to Hawaiian waters as balmy as 69.8 degrees; and makos inhabit seas as warm as 80.6 degrees.

Marine Life Facing Mass Extinction as a Result of Global Warming

In June 2011, Thair Shaikh, reported in CNN, “Marine life is under severe threat from global warming, pollution and habitat loss, with a high risk of "major extinctions" according to a distinguished group of marine scientists who met at Oxford University, England, in April to discuss the impact of human activity on the world's oceans. The meeting, led by the International Programme on the State of the Ocean (IPSO), examined the combined effects of pollution, acidification, ocean warming, over-fishing and depleting levels of oxygen in the water. [Source: Thair Shaikh, CNN, June 21, 2011, Marlowe Hood, AFP, June 20, 2011]

Dying coral reefs, biodiversity ravaged by invasive species, expanding open-water "dead zones," toxic algae blooms, the massive depletion of big fish stocks are all are accelerating, the panel said. These symptoms, moreover, could be the harbinger of wider disruptions in the interlocking web of biological and chemical interactions that scientists now call the Earth system. The panel found that oceanic conditions are similar to those of "previous major extinctions of species in Earth's history," and that we face losing marine species and entire marine ecosystems, such as coral reefs, within a single generation. The interim report, produced in partnership with the International Union for Conservation of Nature (IUCN), was presented to the U.N.

Three main drivers are sickening the global marine environment, and all are a direct consequence of humans activity: global warming, acidification and a dwindling level oxygen, a condition known as hypoxia. The study also said that the speed of decline of marine ecosystems is faster than predicted. Alex Rogers, IPSO's scientific director, said: "The oceans are a common heritage of mankind. The extinction threat we believe is real." Rogers, professor of Conservation Biology at the Department Of Zoology, University of Oxford, told CNN: "The rate of change we are seeing in the quantities of carbon dioxide going into the atmosphere and then being absorbed into the oceans is so great that it is difficult to compare what is happening now with what has happened in the past but we do know that past disturbances in the carbon cycle have been a feature of mass extinction events."

Vaquita, only 20 or so left
According to the panel — which consisted of 27 marine experts from 18 organizations — most if not all the five "global mass extinctions" in Earth's history were probably caused by the "deadly trio" of global warming, ocean acidification and lack of water oxygen or hypoxia. It states that these three factors are present in the ocean today and gives examples of marine ecosystems suffering severe disturbance, such as the mass "coral bleaching" in 1998 that killed 16 percent of all the world's tropical coral reefs.

"The results are shocking," said Alex Rogers, an Oxford professor who heads IPSO and co-authored the report. "We are looking at consequences for humankind that will impact in our lifetime." "The rate at which carbon is being absorbed is already far greater now than during the last globally significant extinction of marine species 55 million years ago," when some 50 percent of deep-sea life was wiped out, the report said. That event, called the Paleocene-Eocene Thermal Maximum, or PETM, may be an ancient dress rehearsal for future climate change that could be even more abrupt and more damaging, some scientists fear.

"We now face losing marine species and entire marine ecosystems, such as coral reefs, within a single generation," said Daniel Laffoley, head of the International Union for Conservation of Nature's (IUCN) World Commission on Protected Areas, and co-author of the report.

Difference Between a Threatened and Endangered Species

Under the Endangered Species Act (ESA), a species may be listed as either threatened or endangered depending on their risk for extinction. An endangered species is defined as "any species which is in danger of extinction throughout all or a significant portion of its range." Endangered species are automatically protected by prohibitions of several types of "take," including harming, harassing, collecting, or killing, under Section 9 of the ESA. There are some limited exceptions to these rules listed in Section 10 of the ESA. The Kemp's ridley turtle, considered the smallest marine turtle in the world, is listed as an endangered species throughout its range of the Gulf of Mexico and entire U.S. Atlantic seaboard. [Source: NOAA]

The ESA defines a threatened species as "any species which is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range." Threatened species receive protections through separate regulations issued under Section 4(d) of the ESA. These regulations occur separately from the listing and detail what take prohibitions are in effect. Also called 4(d) rules, they can include the same prohibitions under Section 9. Elkhorn coral — a large, branching coral with thick and sturdy antler-like branches — is listed as a threatened species throughout its range.

NOAA scientists use the best scientific and commercial information available as the basis for their listing decisions. Scientists may not consider the economic impact of listing a particular species. A species must be listed if it is threatened or endangered due to any of the following five factors: 1) Present or threatened destruction, modification, or curtailment of its habitat or range; 2) Overutilization for commercial, recreational, scientific, or educational purposes; 3) Disease or predation; 4) Inadequacy of existing regulatory mechanisms; and 5) Other natural or human-made factors affecting its continued existence.

There are approximately 2,150 total species listed under the ESA. NOAA's National Marine Fisheries Service and the U.S. Fish and Wildlife Service share responsibility for implementing the ESA.

Invasive Species

Invasive species are animals or plants from another region of the world that don’t belong in their new environment. They often cause ecological or economic harm in a new environment where it is not native. [Source: NOAA]

Invasive species can harm both the natural resources in an ecosystem as well as threaten human use of these resources. An invasive species can be introduced to a new area via the ballast water of oceangoing ships, intentional and accidental releases of aquaculture species, aquarium specimens or bait, and other means.

Invasive species are capable of causing extinctions of native plants and animals, reducing biodiversity, competing with native organisms for limited resources, and altering habitats. This can result in huge economic impacts and fundamental disruptions of coastal and Great Lakes ecosystems. Invasive species can lead to the extinction of native plants and animals, destroy biodiversity, and permanently alter habitats.

Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA

Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; “Introduction to Physical Oceanography” by Robert Stewart , Texas A&M University, 2008 uv.es/hegigui/Kasper ; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023

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