Marine Described
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.
Marine biology
covers a great deal, from the microscopic, including most zooplankton and phytoplankton, where zooplankton can be
as small as 0.02 micrometers or as big as 2 meters in the case of the sunfish to the huge cetaceans (whales) which
reach up to a reported 48 meters (125 feet) in length.
The habitats studied by marine biology include everything from the tiny layers of surface water in which organisms
and abiotic items may be trapped in surface tension between the ocean and atmosphere, to the depths of the abyssal
trenches, sometimes 10,000 meters or more beneath the surface of the ocean. It studies habitats such as coral reefs,
kelp forests, tidepools, muddy, sandy and rocky bottoms, and the open ocean (pelagic) zone, where solid objects are
rare and the surface of the water is the only visible boundary.
A large amount of all life on Earth exists in the oceans. Exactly how large the proportion is still unknown. While
the oceans comprise about 71% of the Earth's surface, due to their depth they encompass about 300 times the habitable
volume of the terrestrial habitats on Earth.
Many species are economically important to humans, including 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 (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.
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.
Zooplankton tend to be somewhat larger, and not all are microscopic. Many Protozoa are zooplankton
Marine invertebrates
As on land, invertebrates make up a huge portion of all life in the sea. Invertebrate sea life includes
jellyfish and sea anemones; sea worms Mollusca including shellfish, squid, octopus; Crustacea; starfish; sea squirts
or tunicates.
Fish
have evolved very different biological functions from other large organisms. Fish anatomy includes a
two-chambered heart, operculum, secretory cells that produce mucous, swim bladder, scales, fins, lips and eyes.
Fish breathe by extracting oxygen from water through their gills. Fins propel and stabilize the fish in the water.
Well known fish include: sardines, anchovy, ling cod, clownfish (also known as anemonefish), and bottom fish which
include halibut or ling cod. Predators include sharks and barracuda.
Reptiles
which inhabit or frequent the sea include sea turtles, Marine Iguana, sea snakes, and Saltwater Crocodiles. 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, live on or near land rather than in the ocean.
Seabirds
are species of birds adapted to living in the marine environment, examples including 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.
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Below is a typical food chain for the types of animals you could find in a marine environment. From the predators on top all the way down to the producers on the bottom. 
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