182 Productivity and Benthic Organisms
worms or of the shrimps. Nothing also of the predators which invade the area from
the sea and from the air.
Muddy sand and deeper waters are settled by the Syndosmya community. The
name-giving clam is a favored food item of flat-fish - something that certainly would
be hard to tell from the fossil record.
Muddy bottoms in depths of about 20 m are conspicuous by their dense cover of
brittle stars (Amphiura community, Fig. 6.19). Up to 500 individuals lie on a square
meter. They dominate the ecology of the sea floor here, but it is doubtful that this
information would be preserved in the record.
6.9 "Hot Vent" and "Cold Seep" Communities
Animals - thus the conventional wisdom - ultimately live at the expense of photosynthesizing organisms which use the sun's energy to produce organic matter from
C02 and H20. There are exceptions, however. Some animals live strictly on bacteria
which derive their sustenance from chemosynthesis rather than photosynthesis. In
some cases, such bacteria are symbionts.
The most spectacular examples of this type of association have recently been
discovered at deep-sea vents, where hot seawater leaves the basaltic sea floor, after
reacting with it deep inside. During these reactions, oxygen is lost, and sulfate is
reduced (Sect. 10.4.4). Where the water exists, e. g., in "black smokers" (Fig. 6.20)
there is an opportunity to derive energy from the oxidation of the sulfice contained.
Thus, sulfide-oxiding bacteria can thrive here. Certain types of these bacteria live in
great abundance as symbionts within vestimentiferan tube worms (e. g., Riftia pachyptila), and giant clams (e. g., Calyptogena magnifica), among others, and thus
"hot vent" chemosynthesis gives rise to a thriving community of strange (and not so
strange) creatures (cover and Fig. 6.20). The tube worms live entirely on the bacteria
which they harbor - they have no means of extracting food from outside, or digesting
it.
The story of the discovery of vent communities is complex, and begins in the
1970s with a search for undersea hot springs, whose presence was deduced from
temperature anomalies and chemical measurements. The first glimpse of unusual
communities came from a deep-sea photograph (taken by P. Lonsdale) showing remains of large clams in unexpected concentrations, near a spreading center. The
living vent community, in all its exuberance, was first seen in 1977 by the geologist
1. Corliss and associates, diving on the Galapagos spreading center at 2.5 km depth,
in Woods Hole's deep submersible ALVIN.
A search for similar hot springs elsewhere, and associated vent communities, was
highly successful, and we now have descriptions of a variety of such faunas from
different regions, in both the Pacific and the Atlantic. Some 160 species new to
science have been published, mainly mollusks, annelids, and arthropods. Some appear to be closely related to certain Mesozoic shallow water forms.
Many exciting questions were raised as a result of these discoveries. How do these
communities survive, given the fact that hot vents exist for only a short time, on the
worms or of the shrimps. Nothing also of the predators which invade the area from
the sea and from the air.
Muddy sand and deeper waters are settled by the Syndosmya community. The
name-giving clam is a favored food item of flat-fish - something that certainly would
be hard to tell from the fossil record.
Muddy bottoms in depths of about 20 m are conspicuous by their dense cover of
brittle stars (Amphiura community, Fig. 6.19). Up to 500 individuals lie on a square
meter. They dominate the ecology of the sea floor here, but it is doubtful that this
information would be preserved in the record.
6.9 "Hot Vent" and "Cold Seep" Communities
Animals - thus the conventional wisdom - ultimately live at the expense of photosynthesizing organisms which use the sun's energy to produce organic matter from
C02 and H20. There are exceptions, however. Some animals live strictly on bacteria
which derive their sustenance from chemosynthesis rather than photosynthesis. In
some cases, such bacteria are symbionts.
The most spectacular examples of this type of association have recently been
discovered at deep-sea vents, where hot seawater leaves the basaltic sea floor, after
reacting with it deep inside. During these reactions, oxygen is lost, and sulfate is
reduced (Sect. 10.4.4). Where the water exists, e. g., in "black smokers" (Fig. 6.20)
there is an opportunity to derive energy from the oxidation of the sulfice contained.
Thus, sulfide-oxiding bacteria can thrive here. Certain types of these bacteria live in
great abundance as symbionts within vestimentiferan tube worms (e. g., Riftia pachyptila), and giant clams (e. g., Calyptogena magnifica), among others, and thus
"hot vent" chemosynthesis gives rise to a thriving community of strange (and not so
strange) creatures (cover and Fig. 6.20). The tube worms live entirely on the bacteria
which they harbor - they have no means of extracting food from outside, or digesting
it.
The story of the discovery of vent communities is complex, and begins in the
1970s with a search for undersea hot springs, whose presence was deduced from
temperature anomalies and chemical measurements. The first glimpse of unusual
communities came from a deep-sea photograph (taken by P. Lonsdale) showing remains of large clams in unexpected concentrations, near a spreading center. The
living vent community, in all its exuberance, was first seen in 1977 by the geologist
1. Corliss and associates, diving on the Galapagos spreading center at 2.5 km depth,
in Woods Hole's deep submersible ALVIN.
A search for similar hot springs elsewhere, and associated vent communities, was
highly successful, and we now have descriptions of a variety of such faunas from
different regions, in both the Pacific and the Atlantic. Some 160 species new to
science have been published, mainly mollusks, annelids, and arthropods. Some appear to be closely related to certain Mesozoic shallow water forms.
Many exciting questions were raised as a result of these discoveries. How do these
communities survive, given the fact that hot vents exist for only a short time, on the