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Hard-bottom communities , which are most common in the high-energy
intertidal zone , are associated with exposed bedrock
and gravel
deposits.
Soft-bottom communities
are composed of unconsolidated sand and
mud. Most typically , clean sand is populated by a variety of filterfeeding bi-valves , with fewer species of polychaete worms and snails.
The proportion of bivalves decreases in muddier sediment , relative to
the population of snails and worms.
Biology of the open ocean and the deep sea :
The oceanic Realm :
Located far from a supply of river-born nutrients , the surface water of
the oceanic province is poor in nutrients. The open ocean is a biological
desert , with few plants . Because of the great depth of the sea bottom
here , the sparse plant life is entirely planktonic . There are no seaweeds
–with one important exception –the floating sargassum Gulfweed. The
principal
phytoplankton
are
diatoms
,
dinoflagellates
and
Coccolithophores. Diatoms are the predominant plants in shallow waters
of the coast and the shelf. However , their proportion relative to other
phytoplankton drops off shraply with distance from land, and
Dinoflgellates and Coccolithophores become equally important.
After the plants , the most abundant organisms in the oceanic realm are
the herbivorous zooplankton , particularly Foraminifera and radiolaria .
In turns , forams and and radiolaria are preyed upon
by larger
Zooplankton , most notably the copepods.
Many species of zooplankton in the open ocean , such as epipelagic
euphasiids , display latitudianl distribution patterns. A variety of
carnivores , such as arrow worms ,sea butterflies ,and amphipods
occupy the higher trophic levels. Top predators , including mackerel ,
siquid , jellyfish , tuna , porpoises ,sharks ,and Humans , complete the
long food web of the open ocean .
Dysphotic animals include crustaceans , such as prawns, shrimps ,
copepods , amphipods , and ostracods (small bi-valve crustaceans) .
Squids and fishes are also common.