Marine biology is the scientific study of
organisms in the ocean or other marine or
brackish bodies of water. 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.
Marine biology differs from marine ecology
as marine ecology is focused on how organisms
interact with each other and the environment,
while biology is the study of the organisms
themselves.
A large proportion of all life on Earth exists
in the ocean. Exactly how large the proportion
is unknown, since many ocean species are still
to be discovered. The ocean is a complex three-dimensional
world covering about 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 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 coral reefs, kelp
forests, seagrass meadows, the surrounds of
seamounts and thermal vents, tidepools, 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
phytoplankton and zooplankton to huge cetaceans
30 meters in length.
Marine life is 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 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 food fish. It is also becoming
understood that the well-being of marine organisms
and other organisms are linked in very 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 and of
air. Large areas beneath the ocean surface
still remain effectively unexplored.
History
The earliest instances of the study of Marine
Biology can be traced back to Aristotle who
made several contributions which laid the
foundation for many future discoveries and
were the first big steps in the early exploration
period of the ocean and marine life. British
naturalist, Edward Forbes was also a key player
in the history of marine biology and is considered
by many as the founder of the science of oceanography
and marine biology. Overall, 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 some of the
most significant is the H.M.S Beagle where
Charles Darwin came up with his theories of
evolution and on the formation of coral reefs.
Another important expedition is the H.M.S
Challenger where findings of unexpectedly
high species diversity of fauna stimulated
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 extremely important for the history
of marine biology but naturalists were still
limited in their studies simply because they
lacked certain technology that would allow
them to accurately examine the species that
lurked the deep parts of the oceans.
The creation of marine labs was important
because marine scientists had places to conduct
research and process their specimens from
expeditions. One of the most important marine
labs is Woods Hole Oceanographic Institute
where scientists stayed and conducted years
of significant research and made many important
findings. There were also many technological
advances that further enhanced the study of
marine biology. For example, sound navigation
ranging, scuba diving gear, submersibles and
remotely operated vehicles, to name a few,
are some of the more impactful technologies
in marine biology which allowed naturalists
to explore depths of the oceans that people
once thought never existed
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.
Other subfields study the physical effects
of continual immersion in sea 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.
Recent marine biotechnology has focused largely
on marine biomolecules, 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 and
is closely linked to oceanography. It also
encompasses many ideas from ecology. Fisheries
science and marine conservation can be considered
partial offshoots of marine biology. Marine
Chemistry, Physical oceanography and Atmospheric
sciences are closely related to this field.
Animals
Birds
Birds adapted to living in the marine environment
are often referred to as seabirds. Examples
include albatross, penguins, 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.
Fish
Fish anatomy includes a two-chambered heart,
operculum, swim bladder, scales, fins, lips,
eyes and secretory cells that produce mucous.
Fish breathe by extracting oxygen from water
through their gills. Fins propel and stabilize
the fish in the water. Many fish fall under
two major categories - Elasmobranchii and
Teleostei.
A reported 32,700 species of fish have been
described, more than the combined total of
all other vertebrates. About 60% of fish species
are saltwater fish.
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
anemones; Ctenophora; sea worms including
the phyla Platyhelminthes, Nemertea, Annelida,
Sipuncula, Echiura, Chaetognatha, and Phoronida;
Mollusca including shellfish, squid, octopus;
Arthropoda including Chelicerata and Crustacea;
Porifera; Bryozoa; Echinodermata including
starfish; and Urochordata including sea squirts
or tunicates.
Mammals
There are five main types of marine mammals.
Cetaceans include toothed whales, such as
the Sperm Whale, dolphins, and porpoises such
as the Dall's porpoise. Cetaceans also include
baleen whales, such as the Gray Whale, Humpback
Whale, and Blue Whale.
Sirenians include manatees, the Dugong, and
the extinct Steller's Sea Cow.
Seals, sea lions, and the Walrus are all considered
pinnipeds.
The Sea Otter is a member of the Family Mustelidae,
which includes weasels and badgers.
The Polar Bear is sometimes considered a marine
mammal because of its dependence on the sea.
Reptiles
Reptiles which inhabit or frequent the sea
include sea turtles, sea snakes, terrapins,
the marine iguana, and the saltwater crocodile.
Most extant marine reptiles, except for some
sea snakes, are oviparous 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.
Some extinct marine reptiles, such as ichthyosaurs,
evolved to be viviparous and had no requirement
to return to land.
Fungi
Over 1500 species of fungi are known from
marine environments. These parasitize 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 metabolites is produced by marine
fungi.
Plants and algae
Plant 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 in the ocean,
such as Sargassum and kelp, which are commonly
known as seaweeds that creates kelp forests.
The non algae plants that survive in the sea
are often found in shallow waters, such as
the seagrasses. These plants have adapted
to the high salinity of the ocean environment.
The intertidal zone is also a good place to
find plant life in the sea, where mangroves
or cordgrass or beach grass might grow. Microscopic
algae and plants provide important habitats
for life, sometimes acting as hiding and foraging
places for larval forms of larger fish and
invertebrates.
Microscopic life
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 is better understood
due to their critical position as the most
numerous primary producers on Earth. Phytoplankton
are categorized into cyanobacteria, various
types of algae, diatoms, dinoflagellates,
euglenoids, coccolithophorids, cryptomonads,
chrysophytes, chlorophytes, prasinophytes,
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 are also phytoplankton; the distinction
between plants and animals 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.
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.
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 habitats. Pelagic
habitats are found near the surface or in
the open water column, away from the bottom
of the ocean. Demersal habitats are near or
on the bottom of the ocean. An organism living
in a pelagic habitat is said to be a pelagic
organism, as in pelagic fish. Similarly, an
organism living in a demersal habitat is said
to be a demersal organism, as in demersal
fish. Pelagic habitats are intrinsically shifting
and ephemeral, depending on what ocean currents
are doing.
Marine habitats can be modified by their inhabitants.
Some marine organisms, like corals, kelp and
seagrasses, are ecosystem engineers which
reshape the marine environment to the point
where they create further habitat for other
organisms.
Intertidal and shore
Intertidal zones, those areas close to shore,
are constantly being exposed and covered by
the ocean's tides. A huge array of life lives
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.
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. Much of the aphotic
zone's energy is supplied by the open ocean
in the form of detritus.
Deep sea and trenches
The deepest recorded oceanic trench measured
to date is the Mariana Trench, near the Philippines,
in the Pacific Ocean at 10,924 m. At such
depths, water pressure is extreme and there
is no sunlight, but some life still exists.
A white flatfish, a shrimp and a jellyfish
were seen by the American crew of the bathyscaphe
Trieste when it dove to the bottom in 1960.
Other notable oceanic trenches include Monterey
Canyon, in the eastern Pacific, the Tonga
Trench in the southwest at 10,882 m, the
Philippine Trench, the Puerto Rico Trench
at 8,605 m, the Romanche Trench at 7,760 m,
Fram Basin in the Arctic Ocean at 4,665 m,
the Java Trench at 7,450 m, and the South
Sandwich Trench at 7,235 m.
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 seamounts
that rise from the depths, where fish and
other sea life congregate to spawn and feed.
Hydrothermal vents along the mid-ocean ridge
spreading centers act as oases, as do their
opposites, cold seeps. Such places support
unique biomes and many new microbes and other
lifeforms have been discovered at these locations
.
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. 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 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.
For example, it is still largely unknown where
sea turtles and some sharks travel. Tracking
devices do not work for some life forms, and
the ocean is not friendly to technology. This
is important to 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 far away.
See also
Lists
References
External links
Smithsonian Ocean Portal
Marine Conservation Society
Marine biology at DMOZ
Marine Ecology - an evolutionary perspective
Free special issue: Marine Biology in Time
and Space
Creatures of the deep ocean – National Geographic
documentary, 2010.
