As land-based creatures, we often underestimate how much of the Earth is water, and specifically salt-water. About 71% of the Earth's surface is ocean, but the seas of the world comprise by far the greatest amount of inhabitable environment--about 300 times that of land. Small wonder that the waters from which life arose are teeming with a variety of environments and organisms.
The study of ocean organisms and their environment began about one hundred years ago when Karl Moebius, a fisheries biologist, recognized circumstances like an oyster bed as a natural entity, and proposed the word "biocoenosis." In about 1866 Ernst Haeckel (1834-1919) developed the idea of ecology and ecosystems. Ecosystems in the ocean are quite varied, from estuaries to far off-shore regions, and from the surface to the cold, dark depths of the ocean. Oceanographers divide the ocean into zones based on these differences, and study the types of organisms found in each. There have been many zones named, but five that are fairly standard.
The Tidal zone may be an estuary (a semi-enclosed basin where fresh water mixes with seawater), or a salt marsh, or the like next to shore. This zone is very subject to tides, wind, waves, and fresh water input from streams and rivers, and also most subject to pollution, oil spills, and other environmental catastrophes. Marine organisms with hard shells that have adapted to a changing environment flourish here, such as barnacles, crabs, anchored seaweed, and starfish.
The Neritic zone is water above the continental shelf, which extends off-shore some distance before it drops off rapidly into the deep ocean floor. Seawater in this region reaches about 300 to 600 ft (100 to 200 m) below sea level. This zone does have some influence from nearby shores and input from coastal rivers and estuaries, and contains protoplankton, seaweed communities, coral reefs, jelly fish, and shrimp, among other organisms. In general, species diversity tends to decrease as one leaves the shore, as the food web (see food chain becomes supported by the planktonic production.
About 80% of the ocean's surface is above water greater than 600 ft (200 m) in depth. The Open ocean zone is the top layer of the ocean, but far away from land, and it is the largest of marine environments. It is exposed to, and influenced by, sunlight, air, and atmospheric circulation patterns. Seas--water bodies smaller than oceans but which has a unique features--are included in this zone. Animals which live in the Open ocean zone include whales, dolphins, Portuguese-man-o-war, swordfish, seals, and tuna.
As one goes deeper in the ocean there is less and less sunlight, and eventually photosynthesis becomes impossible. This is the Aphotic zone, often divided into several other zones depending on depth. The Aphotic zone is the middle layer of the ocean, occupying the region from about 600 ft (200 m) in depth to about 12,000 ft (4,000 m), but the true Aphotic zone starts wherever light penetration stops. Marine animals commonly found in this zone are large squid, octopus, and lantern fish.
The bottom layer of the ocean, the Abyssal zone, is completely dark. The deepest ocean depths are about 33,000 ft (10,000 m), or over 6 miles. Its temperature can be as low as 27° F (-3° C) (still liquid because of the great pressure of the water above it). Animals found in this zone are, for example, tubeworms, anglerfish, some types of clams, gulper, and grenadier, generally found at this depth throughout the world.
The ocean is the least unexplored area on Earth, as well as a global resource that crosses all political and international boundaries. It also presents unique scientific challenges as its secrets are gradually revealed.
This is the complete article, containing 609 words
(approx. 2 pages at 300 words per page).
