Marine biology is the scientific study of the biology of , organisms in the . Given that in many , families and have some species that live in the sea and others that live on land, marine biology classifies species based on the rather than on . A large proportion of all lives in the ocean. The exact size of this ''large proportion'' is unknown, since many ocean species are still to be discovered. The ocean is a complex three-dimensional world covering approximately 71% of the Earth's surface. The habitats studied in marine biology include everything from the tiny layers of surface water in which organisms and abiotic items may be trapped in between the ocean and atmosphere, to the depths of the es, sometimes 10,000 meters or more beneath the surface of the ocean. Specific habitats include , s, s, , the surrounds of s and s, s, muddy, sandy and rocky bottoms, and the open ocean () zone, where solid objects are rare and the surface of the water is the only visible boundary. The organisms studied range from microscopic and to huge (whales) in length. is the study of how marine organisms interact with each other and the environment. Marine life is a vast resource, providing food, medicine, and raw materials, in addition to helping to support and all over the world. At a fundamental level, marine life helps determine the very nature of our planet. Marine organisms contribute significantly to the , and are involved in the regulation of the Earth's . lines are in part shaped and protected by marine life, and some marine organisms even help create new land. Many species are economically important to humans, including both finfish and shellfish. It is also becoming understood that the well-being of marine organisms and other organisms are linked in fundamental ways. The human body of knowledge regarding the relationship between life in the sea and important cycles is rapidly growing, with new discoveries being made nearly every day. These cycles include those of matter (such as the ) and of air (such as , and movement of energy through s including the ocean). Large areas beneath the ocean surface still remain effectively unexplored.

Biological oceanography

Marine biology can be contrasted with . is a field of study both in marine biology and in biological oceanography. Biological oceanography is the study of how organisms affect and are affected by the , , and of the . Biological oceanography mostly focuses on the s within the ocean; looking at how they are affected by their environment and how that affects larger marine creatures and their ecosystem.Lalli, Carol M., and Timothy R. Parsons. "Introduction." Biological Oceanography: An Introduction. First Edition ed. Tarrytown, New York: Pergamon, 1993. 7-21. Print. Biological oceanography is similar to marine biology, but it studies ocean life from a different perspective. Biological oceanography takes a bottom up approach in terms of the food web, while marine biology studies the ocean from a top down perspective. Biological oceanography mainly focuses on the ecosystem of the ocean with an emphasis on plankton: their diversity (morphology, nutritional sources, motility, and metabolism); their productivity and how that plays a role in the global carbon cycle; and their distribution (predation and life cycle). Biological oceanography also investigates the role of microbes in food webs, and how humans impact the ecosystems in the oceans.

Marine habitats

Marine habitats can be divided into and habitats. Coastal habitats are found in the area that extends from the to the edge of the . Most marine life is found in coastal habitats, even though the shelf area occupies only seven percent of the total ocean area. Open ocean habitats are found in the deep ocean beyond the edge of the continental shelf. Alternatively, marine habitats can be divided into and habitats. Pelagic habitats are found near the surface or in the open , away from the bottom of the ocean and affected by s, while demersal habitats are near or on the bottom. Marine habitats can be modified by their inhabitants. Some marine organisms, like corals, kelp and sea grasses, are s which reshape the marine environment to the point where they create further habitat for other organisms.

Intertidal and near shore

s, the areas that are close to the shore, are constantly being exposed and covered by the ocean's . A huge array of life can be found within this zone. Shore habitats span from the upper intertidal zones to the area where land vegetation takes prominence. It can be underwater anywhere from daily to very infrequently. Many species here are scavengers, living off of sea life that is washed up on the shore. Many land animals also make much use of the shore and intertidal habitats. A subgroup of organisms in this habitat bores and grinds exposed rock through the process of .


are also near shore and influenced by the . An estuary is a partially enclosed coastal body of water with one or more rivers or streams flowing into it and with a free connection to the open sea. Estuaries form a transition zone between freshwater river environments and saltwater maritime environments. They are subject both to marine influences—such as tides, waves, and the influx of saline water—and to riverine influences—such as flows of fresh water and sediment. The shifting flows of both sea water and fresh water provide high levels of nutrients both in the water column and in sediment, making estuaries among the most productive natural habitats in the world.


s comprise some of the densest and most diverse habitats in the world. The best-known types of reefs are s which exist in most tropical waters; however, reefs can also exist in cold water. Reefs are built up by s and other -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 s. Coral reefs also support a huge community of life, including the corals themselves, their symbiotic , tropical fish and many other organisms. Much attention in marine biology is focused on coral reefs and the weather phenomenon. In 1998, coral reefs experienced the most severe mass bleaching events on record, when vast expanses of reefs across the world died because sea surface temperatures rose well above normal. Some reefs are recovering, but scientists say that between 50% and 70% of the world's coral reefs are now endangered and predict that could exacerbate this trend.

Open ocean

The open ocean is relatively unproductive because of a lack of nutrients, yet because it is so vast, in total it produces the most primary productivity. The open ocean is separated into different zones, and the different zones each have different ecologies. Zones which vary according to their depth include the , , , , and zones. Zones which vary by the amount of light they receive include the and s. Much of the aphotic zone's energy is supplied by the open ocean in the form of .

Deep sea and trenches

The deepest recorded measured to date is the , near the , in the at . At such depths, is extreme and there is no sunlight, but some life still exists. A white , a shrimp and a jellyfish were seen by the American crew of the ' when it dove to the bottom in 1960. In general, the deep sea is considered to start at the , 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 known as . Marine life also flourishes around s that rise from the depths, where fish and other sea life congregate to spawn and feed. s along the spreading centers act as , as do their opposites, . Such places support unique s and many new s and other lifeforms have been discovered at these locations.

Marine life

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. For this reason marine biology encompasses not only organisms that live only in a marine environment, but also other organisms whose lives revolve around the sea.

Microscopic life

As inhabitants of the largest environment on Earth, microbial marine systems drive changes in every global system. Microbes are responsible for virtually all the that occurs in the ocean, as well as the cycling of , , and other and trace elements. Microscopic life undersea is incredibly diverse and still poorly understood. For example, the role of es in marine ecosystems is barely being explored even in the beginning of the 21st century. The role of is better understood due to their critical position as the most numerous on Earth. Phytoplankton are categorized into (also called blue-green algae/bacteria), various types of (red, green, brown, and yellow-green), s, s, , s, s, s, s, s, and s. tend to be somewhat larger, and not all are microscopic. Many are zooplankton, including dinoflagellates, s, ns, and s. Some of these (such as dinoflagellates) are also phytoplankton; the distinction between plants and animals often breaks down in very small organisms. Other zooplankton include s, s, , s, s, , and s such as s. Many larger animals begin their life as zooplankton before they become large enough to take their familiar forms. Two examples are e and sea stars (also called ).

Plants and algae

Microscopic algae and plants provide important habitats for life, sometimes acting as hiding places for larval forms of larger fish and foraging places for invertebrates. Algal life is widespread and very diverse under the ocean. Microscopic photosynthetic algae contribute a larger proportion of the world's photosynthetic output than all the terrestrial forests combined. Most of the occupied by sub plants on land is actually occupied by macroscopic in the ocean, such as ' and , which are commonly known as s that create s. Plants that survive in the sea are often found in shallow waters, such as the es (examples of which are eelgrass, ', and turtle grass, ''Thalassia''). These plants have adapted to the high salinity of the ocean environment. The is also a good place to find plant life in the sea, where or or might grow.


As on land, make up a huge portion of all life in the sea. Invertebrate sea life includes such as and s; ; s including the , , , , , , and ; including , , ; including and ; ; ; including starfish; and including s or s. Invertebrates have no backbone. There are over a million species.


Over 1500 species of are known from marine environments. These are parasitic on or animals, or are s on algae, corals, protozoan cysts, sea grasses, wood and other substrata, and can also be found in . Spores of many species have special appendages which facilitate attachment to the substratum. A very diverse range of unusual secondary s is produced by marine fungi.



A reported , including and , had been described by 2016, more than all other vertebrates combined. About 60% of fish species live in saltwater.


s which inhabit or frequent the sea include s, s, s, the , and the . Most marine reptiles, except for some sea snakes, are and need to return to land to lay their eggs. Thus most species, excepting sea turtles, spend most of their lives on or near land rather than in the ocean. Despite their marine adaptations, most sea snakes prefer shallow waters nearby land, around islands, especially waters that are somewhat sheltered, as well as near estuaries.Stidworthy J. 1974. Snakes of the World. Grosset & Dunlap Inc. 160 pp. . tp://ftp.fao.org/docrep/fao/009/y0870e/y0870e65.pdf Sea snakesa
Food and Agriculture Organization of the United Nations
Accessed 7 August 2007.
Some marine reptiles, such as s, evolved to be and had no requirement to return to land.


Birds adapted to living in the are often called s. Examples include , s, s, and s. Although they spend most of their lives in the ocean, species such as s can often be found thousands of miles inland.


There are five main types of marine mammals, namely ns (s and s); s such as s; s including seals and the ; s; and the . All are air-breathing, and while some such as the can dive for prolonged periods, all must return to the surface to breathe.


The is large, and thus there are many sub-fields of marine biology. Most involve studying specializations of particular animal groups, such as , and . Other subfields study the physical effects of continual immersion in and the ocean in general, adaptation to a salty environment, and the effects of changing various oceanic properties on marine life. A subfield of marine biology studies the relationships between oceans and ocean life, and global warming and environmental issues (such as displacement). Recent marine has focused largely on marine s, especially s, that may have uses in medicine or engineering. Marine environments are the home to many exotic biological materials that may inspire s.

Related fields

Marine biology is a branch of . It is closely linked to , especially , and may be regarded as a sub-field of . It also encompasses many ideas from . and can be considered partial offshoots of marine biology (as well as ). Marine Chemistry, Physical oceanography and Atmospheric sciences are closely related to this field.

Distribution factors

An active research topic in marine biology is to discover and map the s of various species and where they spend their time. Technologies that aid in this discovery include s, s, and a variety of other . Marine biologists study how the s, s and many other oceanic factors affect ocean life forms, including their growth, distribution and well-being. This has only recently become technically feasible with advances in 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 spend different parts of their life cycles especially in the infant and juvenile years. For example, it is still largely unknown where juvenile s and some year-1 s travel. Recent advances in underwater tracking devices are illuminating what we know about marine organisms that live at great Ocean depths. The information that s give aids in certain time of the year fishing closures and development of a . This data is important to both scientists and fishermen because they are discovering that by restricting commercial fishing in one small area they can have a large impact in maintaining a healthy fish population in a much larger area.


The study of marine biology dates back to (384–322 BC), who made around , laying the foundation for many future discoveries. In 1768, (1744–1774) published the ''Historia Fucorum'', the first work dedicated to marine and the first book on marine biology to use the new of . It included elaborate illustrations of seaweed and marine algae on folded leaves. The British naturalist (1815–1854) is generally regarded as the founder of the science of marine biology. The pace of oceanographic and marine biology studies quickly accelerated during the course of the 19th century. The observations made in the first studies of marine biology fueled the and exploration that followed. During this time, a vast amount of knowledge was gained about the life that exists in the oceans of the world. Many voyages contributed significantly to this pool of knowledge. Among the most significant were the voyages of where came up with his theories of and on the formation of . Another important expedition was undertaken by , where findings were made of unexpectedly high among stimulating much theorizing by population ecologists on how such varieties of life could be maintained in what was thought to be such a hostile environment. This era was important for the history of marine biology but naturalists were still limited in their studies because they lacked technology that would allow them to adequately examine species that lived in deep parts of the oceans. The creation of marine laboratories was important because it allowed marine biologists to conduct research and process their specimens from expeditions. The oldest marine laboratory in the world, , was established in France in 1872. In the United States, the dates back to 1903, while the prominent was founded in 1930. The development of technology such as sound navigation ranging, scuba diving gear, submersibles and remotely operated vehicles allowed marine biologists to discover and explore life in deep oceans that was once thought to not exist.

See also

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Further references

* Morrissey J and Sumich J (2011
''Introduction to the Biology of Marine Life''
Jones & Bartlett Publishers. . * Mladenov, Philip V., Marine Biology: A Very Short Introduction, 2nd edn (Oxford, 2020; online edn, Very Short Introductions online, Feb. 2020), http://dx.doi.org/10.1093/actrade/9780198841715.001.0001, accessed 21 Jun. 2020.

External links

Smithsonian Ocean Portal

Marine Conservation Society
Marine Ecology - an evolutionary perspective

Free special issue: Marine Biology in Time and Space

Creatures of the deep ocean
– ''National Geographic'' documentary, 2010.

- From the University of Washington Library
Marine Training Portal
- Portal grouping training initiatives in the field of Marine Biology {{DEFAULTSORT:Marine Biology Oceanographical terminology