Marine biology is the scientific study of the plants, animals, and other organisms that live in the ocean. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather than on taxonomy.

There are many practical reasons to study marine biology. Marine life represents a vast resource, providing food, medicine, and raw materials, in addition to helping to support recreation and tourism all over the world. At a fundamental level, marine life helps determine the very nature of our planet. Marine organisms produce much of the oxygen we breathe and probably help regulate the earth's climate. Our shorelines are in part shaped and protected by marine life, and some marine organisms even help create new land. The ocean is vast, and contains many strange and wonderful creatures.

Marine biology covers a great deal, from the microscopic, including plankton and phytoplankton, which can be as small as 0.02 micrometers and are both hugely important as the primary producers of the sea, to the huge cetaceans (whales) which reach up to a reported 33 meters (109 feet) in length.

The habitats studied by marine biology include everything from the tiny layers of surface water in which organisms and abiotic items may be trapped in surface tension between the ocean and atmosphere, to the depths of the abyssal trenches, sometimes 10,000 meters or more beneath the surface of the ocean. It studies habitats such as coral reefs, kelp forests, tidepools, muddy, sandy, and rocky bottoms, and the open ocean (pelagic) zone, where solid objects are rare and the surface of the water is the only visible boundary.

A large proportion of all life on Earth exists in the oceans. Exactly how large is the proportion is still unknown. While the oceans comprise about 71% of the Earth's surface, due to their depth they encompass about 300 times the habitable volume of the terrestrial habitats on Earth.

Many species are economically important to humans, including the food fishes. It is also becoming understood that the well-being of marine organisms and other organisms are linked in very fundamental ways. Human understanding is growing of the relationship between life in the sea and important cycles such as that of matter (such as the carbon cycle), of air (such as Earth's respiration, and movement of energy through ecosystems. Large areas beneath the ocean surface still remain effectively unexplored.)


The marine ecosystem is large, and thus there are many subfields of marine biology. Most involve studying specializations of particular species.
Other subfields study the physical effects of continual immersion in sea water and the ocean in general, adaptation to a salty environment, and the affects of changing various oceanic properties on marine life. A subfield of marine biology studies the relationships between oceans and ocean life, and global weather and environmental issues (such as carbon dioxide displacement).

Recent marine biotechnology has focused largely on marine biomolecules, especially proteins, that may have uses in medicine or engineering. An interesting branch of marine biology is aquaculture. Marine environments are the home to many exotic biological materials that may inspire biomimetic materials.

Related fields

Marine biology is closely linked to both oceanography and biology. It also encompasses ideas from ecology. Fisheries science and marine conservation can be considered partial offshoots of marine biology.


Microscopic life undersea is incredibly varied and still poorly understood. For example, the role of viruses in marine ecosystems is barely being explored even in the beginning of the 21st century.

The role of phytoplankton is better understood due to their critical position as the most numerous primary producers on Earth. Phytoplankton are categorized into cyanobacteria (also called blue-green algae/bacteria), various types of algae: red, green, brown, and yellow-green, diatoms, dinoflagellates, euglenoids, coccolithophorids, cryptomonads, crysomonads, chloromonads, prasinomonads, and silicoflagellates.

Zooplankton tend to be somewhat larger, and not all are microscopic. Many Protozoa are zooplankton, including dinoflagellates, zooflagellates, foraminiferans, and radiolarians. Some of these (such as dinoflaggelates) are also phytoplankton; the plant/animal distinction often breaks down in very small organisms. Other zooplankton include cnidarians, ctenophores, chaetognaths, molluscs, arthropods, urochordates, and annelids such as polychaetes. Many larger animals begin their life as zooplankton before they become large enough to take their familiar forms. Two examples are fish larvae and sea stars (also called starfish).

Plant life

Plant life is relatively rare undersea, most of the niche occupied by plants on land is actually occupied by macroscopic algae in the ocean, such as Sargassum and kelp. The plants that do survive in the sea are often found in shallow waters, such as the seagrasses (examples of which are eelgrass, Zostera, and turtlegrass, Thalassia). The intertidal zone is also a good place to find plant life in the sea, where mangroves or cordgrass might grow.

Other sea life

Other sea life includes Cnidaria such as Jellyfish and sea anemone; Ctenophora; sea worms including phyla: Plathyhelminthes, Nemertea, Annelida, Sipuncula, Echiura, and the Phoronida; Mollusca including shellfish, squid, octopus; Crustaceans; Porifera including sponges, Bryozoa, Echinodermata including starfish; and Urochordata - sea squirts or tunicates.


Fishes inhabit the largest, (by volume) biome on Earth. They have evolved very different biological functions from other large organisms. Fish anatomy includes a two chamber heart, operculum, secretory cells that produce mucous, swim bladder, scales, fins, lips and eyes. Fish breathe by extracting oxygen from water through their gills. Fins propel and stabilize the fish in the water.

Well known fish include: sardines, anchovy, tuna, clownfish (also known as anemonefish), and bottom fish which include halibut and ling cod. Predators include sharks and barracuda.

Marine mammals

There are five main types of marine mammals.

Cetaceans include toothed whales (Suborder Odontoceti), such as the Sperm Whale, dolphins, and porpoises. Cetaceans also include baleen whales (Suborder Mysticeti), such as Gray Whales, Humpback Whales, Dall's porpoise, and Blue Whales.

Sirenians include manatees, the Dugong, and the extinct Steller's Sea Cow. Seals (Family Phocidae), sea lions (Family Otariidae - which also include the fur seals), and the Walrus (Family Odobenidae) are all considered pinnipeds. Sea Otters are members of the Family Mustelidae, which includes weasels and badgers. Finally, Polar Bears (Family Ursidae) are sometimes considered marine mammals because of their dependence on the sea.


Reefs comprise some of the densest and most diverse habitats in the world. The best-known types of reefs are tropical coral reefs which exist in most tropical waters; however, reefs can also exist in cold water. Reefs are built up by corals and other calcium-depositing animals, usually on top of a rocky outcrop on the ocean floor. Reefs can also grow on other surfaces, which has made it possible to create artificial reefs. Coral reefs also support a huge community of life, including the corals themselves, their symbiotic zooxanthellae, tropical fish and many other organisms.

Much attention in marine biology is focused on coral reefs and the El Niño weather phenomenon. In 1998, coral reefs experienced a "once in a thousand years" bleaching event, in which vast expanses of reefs across the Earth died because sea surface temperatures rose well above normal. Some reefs are recovering, but scientists say that 58% of the world's coral reefs are now endangered and predict that global warming could exacerbate this trend.

Deep sea and trenches

The ocean is deep, very deep in some places. The deepest recorded measure to date is the Mariana Trench, near the Philippines, in the Pacific Ocean at 10924 m (35838 ft). At such depths, water pressure is extreme and there is no sunlight, but some life still exists. Small flounder (family Soleidae) fish and shrimp were seen by the American crew of the bathyscaphe Trieste when it dove to the bottom in 1960.
Other notable deeps include Monterey Canyon, in the eastern Pacific, the Tonga Trench in the southwest at 10,882 m (35,702 feet), the Philippine trench, the Puerto Rico Trench at 8605 m (28232 ft), the Romanche Trench at 7760 m (24450 ft), Fram Basin in the Arctic Ocean at 4665 m (15305 ft), the Java Trench at 7450 m (24442 ft), and the South Sandwich Trench at 7235 m (23737 ft).

In general, the deep sea is considered to start at the photic zone, the point where sunlight loses its power of transference through the water. Many life forms that live at these depths have the ability to create their own light. Much life centers around seamounts that rise from the deeps, where fish and other sea life congregate to spawn and feed. Hydrothermal vents in the ocean floor act as oases, as do their opposites, cold seeps. These places support unique biomes and many new microbes have been discovered at there.

Marine biologists are trying to amass a more complete mapping of underwater species with the help of modern techniques. The deepest oceanic depressions are supposed to contain unknown species, possibly also of great potential interest for the theories on evolution.

How oceanic factors affect distribution of various organisms

An active research topic in marine biology is to discover and map the life cycles of various species and where they spend their time. Marine biologists study how the ocean currents, tides and many other oceanic factors affect ocean lifeforms, including their growth, distribution and well-being. This has only recently become technically feasible with advances in GPS and newer underwater visual devices.

Most ocean life breeds in specific places, nests or not in others, spends time as juveniles in still others, and in maturity in yet others. Scientists know little about where many species spent different parts of their life cycles. For example, it is still largely unknown where sea turtles travel. Tracking devices do not work for some life forms, and the ocean is not friendly to technology. But these factors are being overcome in many instances.

History of Life

The chemical evolution from self-catalytic chemicals to life (see Origin of life) is not a part of biological evolution.

Not much is known about the earliest developments in life. However, all existing organisms share certain traits, including cellular structure, and genetic code. Most scientists interpret this to mean all existing organisms share a common ancestor, which had already developed the most fundamental cellular processes, but there is no scientific consensus on the relationship of the three domains of life (Archaea, Bacteria, Eukaryota) or the origin of life. Attempts to shed light on the earliest history of life generally focus on the behavior of macromolecules, particularly RNA, and the behavior of complex systems.

The emergence of oxygenic photosynthesis (around 3 billion years ago) and the subsequent emergence of an oxygen-rich, non-reducing atmosphere can be traced through the formation of banded iron deposits, and later red beds of iron oxides. This was a necessary prerequisite for the development of aerobic cellular respiration, believed to have emerged around 2 billion years ago.

In the last billion years, simple multicellular plants and animals began to appear in the oceans. Soon after the emergence of the first animals, the Cambrian explosion (a period of unrivaled and remarkable, but brief, organismal diversity documented in the fossils found at the Burgess Shale) saw the creation of all the major body plans, or phyla, of modern animals. This event is now believed to have been triggered by the development of the Hox genes. About 500 million years ago, plants and fungi colonized the land, and were soon followed by arthropods and other animals, leading to the development of land ecosystems with which we are familiar.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Marine Biology" and Wikipedia article "Evolution"