54
Food in the dysphotic region is scant, because plant production occurs
far above in the sunlit waters of the photic zone . Many of the small
zooplanktoners rely on fallout of organic detritus from above .
The aphotic zone is constantly dark and cold . Over two thousand
species of animals live here . Many of them are colored red or black .
They include copepods , ostracods , jellyfishes , prawns , mysids ,
amphipods , a variety of swimming worms , and an assortment of oddlooking fishes referred to generally as midwater fishes .
The deep sea bottom :
In addition to their low numbers , several other characteristics typify the
biota of the deep –sea bottom . Available information indicates that most
fauna of the deep ocean reproduce year round, presumably because there
are no seasons. These animals also have smaller broods , grow more
slowly , and live considerably longer than do the fauna of the shallow
shelf bottoms.
Perhaps the least expected discovery has been the species diversity of
deep-sea bottom communities. Although the exact degree of diversity is
debated , biologists agree that it is surprisingly high , given the low
biomass and small populations of the region.
They surmise that the stability of the physical and chemical aspects of
that environment over long periods of time accounts for this unexpected
diversity. In other words, the community of deep –sea floor is likely to
be structured , not by physical variability and perturbations , but by
complex biological interactions among community members.
Consider the heavy predation pressure in the deep sea. When predation
on a group of animals is low, as often occurs on land , the size of the
population can expand , provided other favtors do not limit growth. As
a result , the favored species are likely to outcompete other animal
species for ressources , driving them over time to extinction and thus
reducting the community ’s diversity _ , a concept known as
competitive exclusion.
(source :invitation to oceanography.2006.p : 464,465,468)
Food in the dysphotic region is scant, because plant production occurs
far above in the sunlit waters of the photic zone . Many of the small
zooplanktoners rely on fallout of organic detritus from above .
The aphotic zone is constantly dark and cold . Over two thousand
species of animals live here . Many of them are colored red or black .
They include copepods , ostracods , jellyfishes , prawns , mysids ,
amphipods , a variety of swimming worms , and an assortment of oddlooking fishes referred to generally as midwater fishes .
The deep sea bottom :
In addition to their low numbers , several other characteristics typify the
biota of the deep –sea bottom . Available information indicates that most
fauna of the deep ocean reproduce year round, presumably because there
are no seasons. These animals also have smaller broods , grow more
slowly , and live considerably longer than do the fauna of the shallow
shelf bottoms.
Perhaps the least expected discovery has been the species diversity of
deep-sea bottom communities. Although the exact degree of diversity is
debated , biologists agree that it is surprisingly high , given the low
biomass and small populations of the region.
They surmise that the stability of the physical and chemical aspects of
that environment over long periods of time accounts for this unexpected
diversity. In other words, the community of deep –sea floor is likely to
be structured , not by physical variability and perturbations , but by
complex biological interactions among community members.
Consider the heavy predation pressure in the deep sea. When predation
on a group of animals is low, as often occurs on land , the size of the
population can expand , provided other favtors do not limit growth. As
a result , the favored species are likely to outcompete other animal
species for ressources , driving them over time to extinction and thus
reducting the community ’s diversity _ , a concept known as
competitive exclusion.
(source :invitation to oceanography.2006.p : 464,465,468)
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