Tropical or Reef Habitat:
In warm tropical or subtropical waters, coral
reefs provide habitat for thousands of different species. Many of these
are brightly colored and adapted to very specific ways of life. Like
terrestrial rain forests, reefs are disappearing rapidly as a result of
human activities, including pollution and overfishing.
Temperate Waters:
Warm and cool temperate waters extend between the subtropical
and subpolar regions in each hemisphere. They are highly productive, but support
relatively fewer species than tropical regions. However, populations of individual
species may be extremely high owing to the rapid growth of plankton that provides
food for them.
Open Ocean:
Animals of the open waters have boundaries defined only by water temperature and
salinity. Some species are fast-moving and wide ranging, making feeding or reproductive
migrations over thousands of miles. Because nutrients are more abundant nearer shore,
productivity is higher closer to continents than in the central regions. Thus, there
are relatively fewer organisms of all kinds (especially phytoplankton, microscopic
plants) in the center. This results in much clearer water.
Polar Waters:
Some of the coldest marine waters, the Arctic and Antarctic regions are highly
productive, especially in the spring and fall. Their biological diversity is lower
than other regions, probably because many species cannot survive the extreme conditions.
Those that are successful tend to be very abundant. Whales make feeding migrations
into polar regions in the spring, and leave for warmer waters before winter.
Deep Sea:
The deep sea is cold, dark, and relatively deserted. Because there is no sunlight,
food comes from the surface waters where plants can live; below the photic (lighted) zone,
there are no plants. The animals are all predators; they have evolved many bizarre and
unique structures and behaviors to survive. The discovery 20 years ago of communities of
specialized animals and bacteria living around hydrothermal (hot water) vents in
volcanically active areas provides the best-known example of organisms that do not depend
upon energy derived from sunlight for life.
