Marine biology is the scientific study of thebiology ofmarine life, organisms that inhabit thesea. Given that inbiology manyphyla,families andgenera have some species that live in the sea and others that live on land, marine biology classifies species based on theenvironment rather than ontaxonomy.
A large proportion of alllife on Earth 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,[1] 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 insurface tension between the ocean and atmosphere, to the depths of theoceanic trenches, sometimes 10,000 meters or more beneath the surface of the ocean.
Marine life is a vast resource, providing food, medicine, and raw materials, in addition to helping to supportrecreation andtourism all over the world. At a fundamental level, marine life helps determine the very nature of our planet. Marine organisms contribute significantly to theoxygen cycle, and are involved in the regulation of the Earth'sclimate.[2]Shorelines are in part shaped and protected by marine life, and some marine organisms even help create new land.[3]
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 thecarbon cycle) and of air (such asEarth's respiration, and movement of energy throughecosystems including the ocean). Large areas beneath the ocean surface still remain effectively unexplored.
Marine biology studies species that live inmarine habitats. Most of the Earth's surface is covered byocean, which is the home tomarine life. Oceans average nearly four kilometers in-depth and are fringed with coastlines that run for about360,000 kilometres.[4][5]
Marine biology can be contrasted withbiological oceanography.Marine life is a field of study both in marine biology and in biologicaloceanography. Biological oceanography is the study of how organisms affect and are affected by thephysics,chemistry, andgeology of theoceanographic system. Biological oceanography mostly focuses on themicroorganisms within the ocean; looking at how they are affected by their environment and how that affects larger marine creatures and their ecosystem.[6]
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 onplankton: 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).[6][7][8] Biological oceanography also investigates the role of microbes in food webs, and how humans impact theecosystems in the oceans.[6][9]
Marine habitats can be divided intocoastal andopen ocean habitats. Coastal habitats are found in the area that extends from theshoreline to the edge of thecontinental shelf. 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 intopelagic anddemersal habitats. Pelagic habitats are found near the surface or in the openwater column, away from the bottom of the ocean and affected byocean currents, 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, areecosystem engineers which reshape the marine environment to the point where they create further habitat for other organisms.
Intertidal zones, the areas that are close to the shore, are constantly being exposed and covered by the ocean'stides. 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 ofbioerosion.
Estuaries have shifting flows of sea water and fresh water.
Estuaries are also near shore and influenced by thetides. 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.[10] 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.[11]
Reefs comprise some of the densest and most diverse habitats in the world. The best-known types of reefs aretropicalcoral reefs which exist in most tropical waters; however, reefs can also exist in cold water. Reefs are built up bycorals and othercalcium-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 createartificial reefs. Coral reefs also support a huge community of life, including the corals themselves, their symbioticzooxanthellae, tropical fish and many other organisms.
Much attention in marine biology is focused on coral reefs and theEl Niño weather phenomenon. In 1998, coral reefs experienced the most severe mass bleaching events on record, when vast expanses of reefs across the world died becausesea surface temperatures rose well above normal.[12][13] Some reefs are recovering, but scientists say that between 50% and 70% of the world's coral reefs are now endangered and predict thatglobal warming could exacerbate this trend.[14][15][16][17]
Some representative ocean animal life (not drawn to scale) within their approximate depth-defined ecological habitats.Marine microorganisms exist on the surfaces and within the tissues and organs of the diverse life inhabiting the ocean, across all ocean habitats.[18]
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.[19] Zones which vary according to their depth include theepipelagic,mesopelagic,bathypelagic,abyssopelagic, andhadopelagic zones. Zones which vary by the amount of light they receive include thephotic andaphotic zones. Much of the aphotic zone's energy is supplied by the open ocean in the form ofdetritus.
A deep-seachimaera. Its snout is covered withtiny pores capable of detecting animals by perturbations in electric fields.
The deepest recordedoceanic trench measured to date is theMariana Trench, near thePhilippines, in thePacific Ocean at 10,924 m (35,840 ft). At such depths,water pressure is extreme and there is no sunlight, but some life still exists. A whiteflatfish, a shrimp and a jellyfish were seen by the crew of thebathyscapheTrieste when it dove to the bottom in 1960, which led to scientific debate surrounding the likelihood of bony fish surviving in such deep waters. General scientific consensus has discredited the possible viewing of a flatfish at such depths.[20][21][22][23]
In general, the deep sea is considered to start at theaphotic zone, the point where sunlight loses its power of transference through the water.[24] Many life forms that live at these depths have the ability to create their own light known asbio-luminescence. Marine life also flourishes aroundseamounts that rise from the depths, where fish and other sea life congregate to spawn and feed.Hydrothermal vents along themid-ocean ridge spreading centers act asoases, as do their opposites,cold seeps. Such places support uniquebiomes and many newmicrobes and other lifeforms have been discovered at these locations. There is still much more to learn about the deeper parts of theocean.[25]
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 their environment rather than their 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.
As inhabitants of the largest environment on Earth, microbial marine systems drive changes in every global system. Microbes are responsible for virtually allphotosynthesis that occurs in the ocean, as well as the cycling ofcarbon,nitrogen,phosphorus and othernutrients and trace elements.[26]
Microscopic life undersea is incredibly diverse and still poorly understood. For example, the role ofviruses in marine ecosystems is barely being explored even in the beginning of the 21st century.[27]
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 theniche occupied by sub plants on land is actually occupied by macroscopicalgae in the ocean, such asSargassum andkelp, which are commonly known asseaweeds that createkelp forests.
Plants that survive in the sea are often found in shallow waters, such as theseagrasses (examples of which are eelgrass,Zostera, and turtle grass,Thalassia). These plants have adapted to the high salinity of the ocean environment. Theintertidal zone is also a good place to find plant life in the sea, wheremangroves orcordgrass orbeach grass might grow.
Over 10,000[28] species offungi are known from marine environments.[29] These are parasitic onmarine algae or animals, or aresaprobes on algae, corals, protozoan cysts, sea grasses, wood and other substrata, and can also be found insea foam.[30] Spores of many species have special appendages which facilitate attachment to the substratum.[31] A very diverse range of unusual secondarymetabolites is produced by marine fungi.[32]
Reptiles which inhabit or frequent the sea includesea turtles,sea snakes,terrapins, themarine iguana, and thesaltwater crocodile. Mostextant marine reptiles, except for some sea snakes, areoviparous and need to return to land to lay their eggs. Thus most species, excluding 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.[35][36] Someextinct marine reptiles, such asichthyosaurs, evolved to beviviparous and had no requirement to return to land.
Birds adapted to living in themarine environment are often calledseabirds. Examples includealbatross,penguins,gannets, andauks. Although they spend most of their lives in the ocean, species such asgulls can often be found thousands of miles inland.
Themarine ecosystem is large, and thus there are many sub-fields of marine biology. Most involve studying specializations of particular animal groups, such asphycology,invertebrate zoology andichthyology. Other subfields study the physical effects of continual immersion insea water 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 ascarbon dioxide displacement). Recent marinebiotechnology has focused largely on marinebiomolecules, especiallyproteins, that may have uses in medicine or engineering. Marine environments are the home to many exotic biological materials that may inspirebiomimetic materials.
Through constant monitoring of the ocean, there have been discoveries of marine life which could be used to create remedies for certain diseases such as cancer and leukemia. In addition, Ziconotide, an approved drug used to treat pain, was created from a snail which resides in the ocean.[39]
An active research topic in marine biology is to discover and map thelife cycles of various species and where they spend their time. Technologies that aid in this discovery includepop-up satellite archival tags,acoustic tags, and a variety of otherdata loggers. Marine biologists study how theocean currents,tides 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 inGPS and newer underwater visual devices.[40]
Most ocean life breeds in specific places, nests 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 juvenilesea turtles and somesharks in the first year of their life travel. Recent advances in underwater tracking devices are illuminating what we know about marine organisms that live at great ocean depths.[41] The information thatpop-up satellite archival tags gives aids in fishing closures for certain times of the year and the development ofmarine protected areas. 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 toAristotle (384–322 BC), who mademany observations of life in the sea aroundLesbos, laying the foundation for many future discoveries.[43] In 1768,Samuel Gottlieb Gmelin (1744–1774) published theHistoria Fucorum, the first work dedicated to marinealgae and the first book on marine biology to use the newbinomial nomenclature ofLinnaeus. It included elaborate illustrations of seaweed and marine algae on folded leaves.[44][45] The British naturalistEdward Forbes (1815–1854) is generally regarded as the founder of the science of marine biology.[46] 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 theAge of Discovery 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 ofHMS Beagle whereCharles Darwin came up with his theories ofevolution and on the formation ofcoral reefs.[47] Another important expedition was undertaken byHMSChallenger, where findings were made of unexpectedly highspecies diversity amongfauna 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.[48] 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,Station biologique de Roscoff, was established in Concarneau, France founded by the College of France in 1859.[49] In the United States, theScripps Institution of Oceanography dates back to 1903, while the prominentWoods Hole Oceanographic Institute was founded in 1930.[50] The development of technology such assound navigation and ranging,scuba diving gear,submersibles andremotely operated vehicles allowed marine biologists to discover and explore life in deep oceans that was once thought to not exist.[51] Public interest in the subject continued to develop in the post-war years with the publication ofRachel Carson's sea trilogy (1941–1955).
In 1960, thebathyscapheTrieste descended the furthest point man had yet traveled, bottomingChallenger's Deep at 35,797 feet.[21] The vessel was captained byJacques Piccard andDon Walsh, whose discoveries while at the bottom of the ocean bolstered scientific discussion and interest about life in the hadal zone.[21][22][23]
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^McLusky, D. S.; Elliott, M. (2004).The Estuarine Ecosystem: Ecology, Threats and Management. New York: Oxford University Press.ISBN978-0-19-852508-0.
^ICRS (1998) Statement on Global Coral Bleaching in 1997-1998. International Coral Reef Society, October 15, 1998.
^Bryant, D., Burke, L., McManus, J., et al. (1998) "Reefs at risk: a map-based indicator of threats to the world's coral reefs". World Resources Institute, Washington, D.C.
^Wilkinson, C. R., and Buddemeier, R. W. (1994) "Global Climate Change and Coral Reefs:Implications for People and Reefs". Report of the UNEP-IOC-ASPEI-IUCN Global Task Team on the Implications of Climate Change on Coral Reefs. IUCN, Gland, Switzerland.
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^Moyle, P. B.; Leidy, R. A. (1992). Fiedler, P. L.; Jain, S. A. Jain (ed.).Loss of biodiversity in aquatic ecosystems: Evidence from fish faunas. Chapman and Hall. pp. 128–169.{{cite book}}:|work= ignored (help)CS1 maint: multiple names: authors list (link)
^Stidworthy J. 1974. Snakes of the World. Grosset & Dunlap Inc. 160 pp.ISBN0-448-11856-4.
^Ward, Ritchie R. Into the ocean world; the biology of the sea. 1st ed. New York: Knopf; [distributed by Random House], 1974: 161
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