6 Productivity and Benthic Organisms -
Distribution, Activity,
and Environmental Reconstruction
6.1 The Ocean Habitat
6.1.1 Diversity of Organisms. In the enOimous living space provided by the sea,
there are plankton (drifters), nekton (swimmers), and benthos (bottom-living organisms). Much of the benthos releases eggs and larvae into the plankton - this is the
meroplankton, abundant in coastal waters. The larvae are dispersed by currents; they
settle when their time has come, and start growing on the appropriate solid subtrate.
The meroplankton feeds planktonic and nektonic predators. Conversely, the plankton
feeds the benthos. Thus there is an intimate ecologic relationship between freeswimming and bottom-living organisms. Ultimately, of course, benthic organisms
rely on food produced in surface waters in the sunlit zone (Fig. 6.1). The notable
exception is the deep-sea benthic community at the hot vents of the Mid-Ocean Ridge
(see Sect. 6.9).
On the whole, fewer species developed in the ocean than on land. The living space
of the ocean has fewer nooks and crannies than that on land, and the various parts of
the world ocean are interconnected. Thus there is less opportunitiy for separate evolution from populations from subspecies to species. The greater diversity of land
animals is entirely due to the proliferation of insects (> 75 % of one million animal
species). Of the marine animal species (180000) 98 % are benthic; only 2 % are
planktonic or nektonic.
These numbers, of course, are subject to revision by continuing investigations.
The general trends seem secure, although we do not share the opinion of Pliny the
Elder (23-79 A.D.) who stated, " ... in the whole ocean, as large as it is, there lives
nothing that we do not know."
6.1.2 Productivity and Supply of Organic Matter. Sunlight and nutrients determine
the growth and distribution of organism, because the food chain has its base in the
marine algae. Matter is transferred along this chain from primary production to herbivores, to carnivores, and back to bacteria for recycling. Also, material is transferred
downward in the water column, from the productive zone to the sea floor, mainly by
fecal matter and by aggregates containing planktonic remains.
For every 100 gC produced in the sunlit zone, roughly 30 gC reach the sea floor on
the shelf and the upper slope, but only 1 gC reaches the deep-sea floor (as indicated by
studies with sediment traps). During the long transit downward (order of 2 weeks),
most of the sinking material is oxidized and remineralized. (See Fig. 6.2.)
Distribution, Activity,
and Environmental Reconstruction
6.1 The Ocean Habitat
6.1.1 Diversity of Organisms. In the enOimous living space provided by the sea,
there are plankton (drifters), nekton (swimmers), and benthos (bottom-living organisms). Much of the benthos releases eggs and larvae into the plankton - this is the
meroplankton, abundant in coastal waters. The larvae are dispersed by currents; they
settle when their time has come, and start growing on the appropriate solid subtrate.
The meroplankton feeds planktonic and nektonic predators. Conversely, the plankton
feeds the benthos. Thus there is an intimate ecologic relationship between freeswimming and bottom-living organisms. Ultimately, of course, benthic organisms
rely on food produced in surface waters in the sunlit zone (Fig. 6.1). The notable
exception is the deep-sea benthic community at the hot vents of the Mid-Ocean Ridge
(see Sect. 6.9).
On the whole, fewer species developed in the ocean than on land. The living space
of the ocean has fewer nooks and crannies than that on land, and the various parts of
the world ocean are interconnected. Thus there is less opportunitiy for separate evolution from populations from subspecies to species. The greater diversity of land
animals is entirely due to the proliferation of insects (> 75 % of one million animal
species). Of the marine animal species (180000) 98 % are benthic; only 2 % are
planktonic or nektonic.
These numbers, of course, are subject to revision by continuing investigations.
The general trends seem secure, although we do not share the opinion of Pliny the
Elder (23-79 A.D.) who stated, " ... in the whole ocean, as large as it is, there lives
nothing that we do not know."
6.1.2 Productivity and Supply of Organic Matter. Sunlight and nutrients determine
the growth and distribution of organism, because the food chain has its base in the
marine algae. Matter is transferred along this chain from primary production to herbivores, to carnivores, and back to bacteria for recycling. Also, material is transferred
downward in the water column, from the productive zone to the sea floor, mainly by
fecal matter and by aggregates containing planktonic remains.
For every 100 gC produced in the sunlit zone, roughly 30 gC reach the sea floor on
the shelf and the upper slope, but only 1 gC reaches the deep-sea floor (as indicated by
studies with sediment traps). During the long transit downward (order of 2 weeks),
most of the sinking material is oxidized and remineralized. (See Fig. 6.2.)