Marine biology is the scientific study of the biology of
marine life
Marine life, sea life, or ocean life is the plants, animals and other organisms that live in the salt water of seas or oceans, or the brackish water of coastal estuaries. At a fundamental level, marine life affects the nature of the planet. M ...
, organisms in the
sea. Given that in
biology many
phyla Phyla, the plural of ''phylum'', may refer to:
* Phylum, a biological taxon between Kingdom and Class
* by analogy, in linguistics, a large division of possibly related languages, or a major language family which is not subordinate to another
Phyl ...
,
families and
genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
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.
A large proportion of all
life on Earth Life on Earth may refer to:
Science
* Life
* Earliest known life forms
* Evolutionary history of life
** Abiogenesis
Film and television
* ''Life on Earth'' (film) (''La Vie Sur Terre''), a 1998 Malian film
* ''Life on Earth'' (TV series), a 197 ...
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
surface tension
Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to f ...
between the ocean and atmosphere, to the depths of the
oceanic trenches, sometimes 10,000 meters or more beneath the surface of the ocean. Specific habitats include
estuaries,
coral reefs,
kelp forests,
seagrass meadows, the surrounds of
seamount
A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abru ...
s and
thermal vents,
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. The organisms studied range from microscopic
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
and
zooplankton to huge
cetaceans
Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...
(whales) in length.
Marine ecology 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
recreation
Recreation is an activity of leisure, leisure being discretionary time. The "need to do something for recreation" is an essential element of human biology and psychology. Recreational activities are often done for enjoyment, amusement, or pleasur ...
and
tourism all over the world. At a fundamental level, marine life helps determine the very nature of our planet. Marine organisms contribute significantly to the
oxygen cycle, and are involved in the regulation of the Earth's
climate.
Shorelines 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
carbon cycle) and of air (such as
Earth's respiration, and movement of energy through
ecosystems including the ocean). Large areas beneath the ocean surface still remain effectively unexplored.
Biological oceanography

Marine biology can be contrasted with
biological oceanography.
Marine life
Marine life, sea life, or ocean life is the plants, animals and other organisms that live in the salt water of seas or oceans, or the brackish water of coastal estuaries. At a fundamental level, marine life affects the nature of the planet. M ...
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
physics,
chemistry
Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...
, and
geology of the
oceanographic system. Biological oceanography mostly focuses on the
microorganisms 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
coastal and
open ocean habitats. Coastal habitats are found in the area that extends from the
shoreline to the edge of the
continental shelf
A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...
. 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
pelagic and
demersal
The demersal zone is the part of the sea or ocean (or deep lake) consisting of the part of the water column near to (and significantly affected by) the seabed and the benthos. The demersal zone is just above the benthic zone and forms a layer of ...
habitats. Pelagic habitats are found near the surface or in the open
water column, away from the bottom of the ocean and affected by
ocean 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, are
ecosystem engineer
An ecosystem engineer is any species that creates, significantly modifies, maintains or destroys a habitat. These organisms can have a large impact on species richness and landscape-level heterogeneity of an area. As a result, ecosystem enginee ...
s which reshape the marine environment to the point where they create further habitat for other organisms.
Intertidal and near shore
Intertidal zone
The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...
s, the areas that are close to the shore, are constantly being exposed and covered by the ocean's
tides
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another.
Tide tables can ...
. 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
bioerosion
Bioerosion describes the breakdown of hard ocean substrates – and less often terrestrial substrates – by living organisms. Marine bioerosion can be caused by mollusks, polychaete worms, phoronids, sponges, crustaceans, echinoids, and ...
.
Estuaries
Estuaries are also near shore and influenced by the
tides
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another.
Tide tables can ...
. 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.
Reefs
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 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
global warming 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
epipelagic,
mesopelagic,
bathypelagic
The bathypelagic zone or bathyal zone (from Greek βαθύς (bathýs), deep) is the part of the open ocean that extends from a depth of below the ocean surface. It lies between the mesopelagic above, and the abyssopelagic below. The bathypelagic ...
,
abyssopelagic, and
hadopelagic
The hadal zone, also known as the hadopelagic zone, is the deepest region of the ocean, lying within oceanic trenches. The hadal zone ranges from around below sea level, and exists in long, narrow, topographic V-shaped depressions.
The cumula ...
zones. Zones which vary by the amount of light they receive include the
photic
The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological proc ...
and
aphotic zones. Much of the aphotic zone's energy is supplied by the open ocean in the form of
detritus
In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...
.
Deep sea and trenches

The deepest recorded
oceanic trench measured to date is the
Mariana Trench, near the
Philippines, in the
Pacific Ocean at . At such depths,
water pressure is extreme and there is no sunlight, but some life still exists. A white
flatfish
A flatfish is a member of the Ray-finned fish, ray-finned demersal fish order (biology), order Pleuronectiformes, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the ...
, a shrimp and a jellyfish were seen by the American crew of the
bathyscaphe
A bathyscaphe ( or ) is a free-diving self-propelled deep-sea submersible, consisting of a crew cabin similar to a bathysphere, but suspended below a float rather than from a surface cable, as in the classic bathysphere design.
The float is fi ...
''
Trieste'' when it dove to the bottom in 1960. In general, the deep sea is considered to start at the
aphotic 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 known as
bio-luminescence. Marine life also flourishes around
seamount
A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abru ...
s that rise from the depths, where fish and other sea life congregate to spawn and feed.
Hydrothermal vent
A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...
s along the
mid-ocean ridge spreading centers act as
oases
In ecology, an oasis (; ) is a fertile area of a desert or semi-desert environment'ksar''with its surrounding feeding source, the palm grove, within a relational and circulatory nomadic system.”
The location of oases has been of critical imp ...
, as do their opposites,
cold seeps. Such places support unique
biomes and many new
microbe
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
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
photosynthesis that occurs in the ocean, as well as the cycling of
carbon,
nitrogen,
phosphorus and other
nutrients and trace elements.
Microscopic life undersea is incredibly diverse 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
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
is better understood due to their critical position as the most numerous
primary producers on Earth. Phytoplankton are categorized into
cyanobacteria
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...
(also called blue-green algae/bacteria), various types of
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
(red, green, brown, and yellow-green),
diatom
A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
s,
dinoflagellate
The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...
s,
euglenoids
Euglenids (euglenoids, or euglenophytes, formally Euglenida/Euglenoida, ICZN, or Euglenophyceae, ICBN) are one of the best-known groups of flagellates, which are excavate eukaryotes of the phylum Euglenophyta and their cell structure is typica ...
,
coccolithophorids,
cryptomonads,
chrysophytes,
chlorophyte
Chlorophyta or Prasinophyta is a taxon of green algae informally called chlorophytes. The name is used in two very different senses, so care is needed to determine the use by a particular author. In older classification systems, it refers to a ...
s,
prasinophytes, and
silicoflagellates.
Zooplankton tend to be somewhat larger, and not all are microscopic. Many
Protozoa
Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
are zooplankton, including dinoflagellates,
zooflagellate In some older systems of classification, Zoomastigophora is a phylum (more commonly known as zooflagellates) within the kingdom Protista. Organisms within this group have a spherical, elongated body with a single central nucleus. They are single-ce ...
s,
foraminiferans, and
radiolarians. 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
cnidarian
Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter.
Their distinguishing feature is cnidocytes, specialized cells that th ...
s,
ctenophore
Ctenophora (; ctenophore ; ) comprise a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming (commonly referred to as "combs"), and ...
s,
chaetognaths,
mollusc
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...
s,
arthropods,
urochordates
A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ...
, and
annelid
The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...
s 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
Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish ...
).
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
niche occupied by sub plants on land is actually occupied by macroscopic
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
in the ocean, such as ''
Sargassum'' and
kelp, which are commonly known as
seaweed
Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...
s that create
kelp forests.
Plants that survive in the sea are often found in shallow waters, such as the
seagrasses (examples of which are eelgrass, ''
Zostera
''Zostera'' is a small genus of widely distributed seagrasses, commonly called marine eelgrass, or simply seagrass or eelgrass, and also known as seaweed by some fishermen and recreational boaters including yachtsmen. The genus ''Zostera'' con ...
'', and turtle grass, ''Thalassia''). These plants have adapted to the high salinity of the ocean environment. The
intertidal zone
The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...
is also a good place to find plant life in the sea, where
mangroves or
cordgrass or
beach grass
''Ammophila'' (synonymous with ''Psamma'' P. Beauv.) is a genus of flowering plants consisting of two or three very similar species of grasses. The common names for these grasses include marram grass, bent grass, and beachgrass. These grasses ar ...
might grow.
Invertebrates
As on land,
invertebrates make up a huge portion of all life in the sea. Invertebrate sea life includes
Cnidaria such as
jellyfish and
sea anemone
Sea anemones are a group of predation, predatory marine invertebrates of the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classifi ...
s;
Ctenophora;
sea worms including the
phyla Phyla, the plural of ''phylum'', may refer to:
* Phylum, a biological taxon between Kingdom and Class
* by analogy, in linguistics, a large division of possibly related languages, or a major language family which is not subordinate to another
Phyl ...
Platyhelminthes,
Nemertea,
Annelida,
Sipuncula,
Echiura,
Chaetognatha, and
Phoronida;
Mollusca
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...
including
shellfish
Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater envir ...
,
squid
True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
,
octopus
An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttle ...
;
Arthropoda including
Chelicerata and
Crustacea
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...
;
Porifera
Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through th ...
;
Bryozoa;
Echinodermata including starfish; and
Urochordata
A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ...
including
sea squirts or
tunicates. Invertebrates have no backbone. There are over a million species.
Fungi
Over 10,000 species of
fungi are known from marine environments. These are parasitic on
marine algae or animals, or are
saprobes on algae, corals, protozoan cysts, sea grasses, wood and other substrata, and can also be found in
sea foam. Spores of many species have special appendages which facilitate attachment to the substratum. A very diverse range of unusual secondary
metabolite
In biochemistry, a metabolite is an intermediate or end product of metabolism.
The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...
s is produced by marine fungi.
Vertebrates
Fish
A reported
33,400 species of fish, including
bony and
cartilaginous fish
Chondrichthyes (; ) is a class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed of bone tissue ...
, had been described by 2016, more than all other vertebrates combined. About 60% of fish species live in saltwater.
Reptiles
Reptile
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
s which inhabit or frequent the sea include
sea turtles,
sea snakes,
terrapins, the
marine iguana, and the
saltwater crocodile. Most
extant
Extant is the opposite of the word extinct. It may refer to:
* Extant hereditary titles
* Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English
* Extant taxon, a taxon which is not extinct, ...
marine reptiles, except for some sea snakes, are
oviparous
Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...
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
extinct
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
marine reptiles, such as
ichthyosaur
Ichthyosaurs (Ancient Greek for "fish lizard" – and ) are large extinct marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' – a designation introduced by Sir Richard Owen in 1842, altho ...
s, evolved to be
viviparous and had no requirement to return to land.
Birds
Birds adapted to living in the
marine environment are often called
seabirds. Examples include
albatross
Albatrosses, of the biological family Diomedeidae, are large seabirds related to the procellariids, storm petrels, and diving petrels in the order Procellariiformes (the tubenoses). They range widely in the Southern Ocean and the North Pacifi ...
,
penguin
Penguins (order (biology), order List of Sphenisciformes by population, Sphenisciformes , family (biology), family Spheniscidae ) are a group of Water bird, aquatic flightless birds. They live almost exclusively in the Southern Hemisphere: on ...
s,
gannets, and
auks. Although they spend most of their lives in the ocean, species such as
gulls can often be found thousands of miles inland.
Mammals
There are five main types of marine mammals, namely
cetacea
Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...
ns (
toothed whales and
baleen whale
Baleen whales (systematic name Mysticeti), also known as whalebone whales, are a parvorder of carnivorous marine mammals of the infraorder Cetacea (whales, dolphins and porpoises) which use keratinaceous baleen plates (or "whalebone") in their ...
s);
sirenians such as
manatees;
pinnipeds including seals and the
walrus;
sea otter
The sea otter (''Enhydra lutris'') is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between , making them the heaviest members of the weasel family, but among the small ...
s; and the
polar bear
The polar bear (''Ursus maritimus'') is a hypercarnivorous bear whose native range lies largely within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses. It is the largest extant bear specie ...
. All are air-breathing, and while some such as the
sperm whale
The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the genus ''Physeter'' and one of three extant species in the sperm whale famil ...
can dive for prolonged periods, all must return to the surface to breathe.
Subfields
The
marine ecosystem is large, and thus there are many sub-fields of marine biology. Most involve studying specializations of particular animal groups, such as
phycology,
invertebrate zoology and
ichthyology
Ichthyology is the branch of zoology devoted to the study of fish, including bony fish ( Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). According to FishBase, 33,400 species of fish had been described as of Octob ...
. Other subfields study the physical effects of continual immersion in
sea water
Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approx ...
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
carbon dioxide displacement). Recent marine
biotechnology has focused largely on marine
biomolecule
A biomolecule or biological molecule is a loosely used term for molecules present in organisms that are essential to one or more typically biological processes, such as cell division, morphogenesis, or development. Biomolecules include large ...
s, especially
proteins, that may have uses in medicine or engineering. Marine environments are the home to many exotic biological materials that may inspire
biomimetic materials.
Related fields
Marine biology is a branch of
biology. It is closely linked to
oceanography
Oceanography (), also known as oceanology and ocean science, is the scientific study of the oceans. It is an Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynamic ...
, especially
biological oceanography, and may be regarded as a sub-field of
marine science. It also encompasses many ideas from
ecology.
Fisheries science and
marine conservation can be considered partial offshoots of marine biology (as well as
environmental studies
Environmental studies is a multidisciplinary academic field which systematically studies human interaction with the environment. Environmental studies connects principles from the physical sciences, commerce/economics, the humanities, and social ...
). 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
life cycles of various species and where they spend their time. Technologies that aid in this discovery include
pop-up satellite archival tags,
acoustic tags, and a variety of other
data loggers. Marine biologists study how the
ocean 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 in
GPS
The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...
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
sea turtles and some year-1
sharks travel. Recent advances in underwater tracking devices are illuminating what we know about marine organisms that live at great Ocean depths. The information that
pop-up satellite archival tags give aids in certain time of the year fishing closures and development of a
marine protected area. 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.
History

The study of marine biology dates back to
Aristotle (384–322 BC), who made
many observations of life in the sea around
Lesbos, laying the foundation for many future discoveries. In 1768,
Samuel Gottlieb Gmelin (1744–1774) published the ''Historia Fucorum'', the first work dedicated to marine
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
and the first book on marine biology to use the new
binomial nomenclature of
Linnaeus. It included elaborate illustrations of seaweed and marine algae on folded leaves. The British naturalist
Edward Forbes (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
age 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 of where
Charles Darwin came up with his theories of
evolution and on the formation of
coral reefs. Another important expedition was undertaken by
HMS ''Challenger'', where findings were made of unexpectedly high
species diversity among
fauna 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,
Station biologique de Roscoff, was established in Concarneau, France founded by the College of France in 1859. In the United States, the
Scripps Institution of Oceanography
The Scripps Institution of Oceanography (sometimes referred to as SIO, Scripps Oceanography, or Scripps) in San Diego, California, US founded in 1903, is one of the oldest and largest centers for oceanography, ocean and Earth science research ...
dates back to 1903, while the prominent
Woods Hole Oceanographic Institute 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
*
Acoustic ecology
Acoustic ecology, sometimes called ecoacoustics or soundscape studies, is a discipline studying the relationship, mediated through sound, between human beings and their environment. Acoustic ecology studies started in the late 1960s with R. Murr ...
*
Aquaculture
Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
*
Bathymetry
*
Biological oceanography
*
Effects of climate change on oceans
Among the effects of climate change on oceans are: an increase in sea surface temperature as well as ocean temperatures at greater depths, more frequent marine heatwaves, a reduction in pH value, a rise in sea level from ocean warming and ice ...
*
Freshwater biology
*
Modular ocean model
*
Oceanic basin
*
Oceanic climate
An oceanic climate, also known as a marine climate, is the humid temperate climate sub-type in Köppen classification ''Cfb'', typical of west coasts in higher middle latitudes of continents, generally featuring cool summers and mild winters ( ...
*
Phycology
Lists
*
Glossary of ecology
*
Index of biology articles
Biology is the Research, study of life and its processes. Biologists study all aspects of living things, including ''all'' of the many life forms on earth and the processes in them that enable life. These basic processes include the harnessing o ...
*
Large marine ecosystem
*
List of ecologists
This is a list of notable ecologists.
A-D
* John Aber (USA)
* Aziz Ab'Saber (Brazil)
* Charles Christopher Adams (USA)
* Warder Clyde Allee (USA)
* Herbert G. Andrewartha ( Australia)
* Sarah Martha Baker ( UK)
* Fakhri A. Bazzaz (USA)
* ...
*
List of marine biologists
*
List of marine ecoregions (WWF)
*
Outline of biology
*
Outline of ecology
References
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 PortalMarine Conservation Society*
Marine Ecology - an evolutionary perspectiveFree special issue: Marine Biology in Time and SpaceCreatures of the deep ocean– ''National Geographic'' documentary, 2010.
Exploris- From the University of Washington Library
Marine Training Portal- Portal grouping training initiatives in the field of Marine Biology
{{DEFAULTSORT:Marine Biology
Biological oceanography
Fisheries science
Oceanographical terminology