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Reef Zoobenthos
2. Omnivorous molluscs feeding on small seaweeds, filamentous algae,
periphyton and microphytobenthos, on detritus and on small benthic
animals (Trochus, Turbo, Patella, Littorina, Cerithium, Strombus, some
species of muricids, chytons).
3. Predatory benthophages feeding on other molluscs, polychaetes, and
echynoderms (conids, muricids, Morula, Cassis, Cymatum, Charonia,
Bursa, Rapa, Latirus, Mitra, and some other predatory gastropods).
4. Predatory corallovorous gastropods feeding on hard and soft corals
(Oliva, Cyphoma, Heliacus, Epithonium, Drupa).
5. Filter-feeders feeding on microplankton and suspended organic matter
(bivalves, vermetids).
6. Symbiotic molluscs which cover a significant part of their energy
expenditures by the photosynthesis of their algal symbionts (Tridacna,
Corculum). The ratios of these groups varies in different reef sites.
On average, the omnivorous gastropods, phytopages and chitons comprise 30-40% of the total number of molluscan species, the predatory gastropods and corallophages 40-50%, and the filter-feeders
10-20%.
Thus, for the reef commumtJes of molluscs there is a peculiar and
significant predomination of predatory species (Kohn 1968; Kohn and
Levitien 1976). For example, the taxonomic structure of communities of reef
molluscs in the barrier reef off Moorea, French Polynesia, looks as follows
(Ricard and Salvat 1972). On the flat covered with sand and with rear
corals, gastropods were the most numerous. Of the total number of species
of Mollusca (117 species) the percentages for species of the dominating taxa
were: Mitridae 15%, Cerithidae 11 %, Conidae 10%, Muricidae and related
taxa 8%, Cypraeidae 7%, Terebridae 6%, Strombiidae 4%. But as regards
the total number of specimens (not counting the micromolluscs) the
Cypraeidae were most numerous (52%) followed by Cerithiidae with 16%,
Terebridae 4%, and Mitridae 2%. Five dominating species alone formed
75% of the total number of Mollusca. These were: Cypraea oblevata,
Cerithium piperitum, Strombus mutabilis, Terebra sp., and Vermetus
maximus. Three species out of 117 were responsible for 90% of the total
molluscan biomass: Vermetus maximus, Tridacna maxima and Cypraea
obleviata. In the coastal lagoon of the same barrier reef, the bottom of
which was covered by sand with the admixture of detritus and with rear
corals, just the one Cypraea obleviata comprised 60% of the total numer of
species. The number of this gastropod exceeded 100 sp. m- 2 . Other
dominating species in this biotope were: Cerithium piperum, Strombus
mutabilis, Cantharus fumosus, C. coronatum, and Pyramidella sp.
The density of communities, as a rule, drastically varies in different areas
of the reef. Its maximum is usually in the littoral rocky biotopes and in the
wind-stressed reef edges. The vertical cliff slopes are most often densely
colonized by the bivalves, while their horizontal surfaces and the pools in
Reef Zoobenthos
2. Omnivorous molluscs feeding on small seaweeds, filamentous algae,
periphyton and microphytobenthos, on detritus and on small benthic
animals (Trochus, Turbo, Patella, Littorina, Cerithium, Strombus, some
species of muricids, chytons).
3. Predatory benthophages feeding on other molluscs, polychaetes, and
echynoderms (conids, muricids, Morula, Cassis, Cymatum, Charonia,
Bursa, Rapa, Latirus, Mitra, and some other predatory gastropods).
4. Predatory corallovorous gastropods feeding on hard and soft corals
(Oliva, Cyphoma, Heliacus, Epithonium, Drupa).
5. Filter-feeders feeding on microplankton and suspended organic matter
(bivalves, vermetids).
6. Symbiotic molluscs which cover a significant part of their energy
expenditures by the photosynthesis of their algal symbionts (Tridacna,
Corculum). The ratios of these groups varies in different reef sites.
On average, the omnivorous gastropods, phytopages and chitons comprise 30-40% of the total number of molluscan species, the predatory gastropods and corallophages 40-50%, and the filter-feeders
10-20%.
Thus, for the reef commumtJes of molluscs there is a peculiar and
significant predomination of predatory species (Kohn 1968; Kohn and
Levitien 1976). For example, the taxonomic structure of communities of reef
molluscs in the barrier reef off Moorea, French Polynesia, looks as follows
(Ricard and Salvat 1972). On the flat covered with sand and with rear
corals, gastropods were the most numerous. Of the total number of species
of Mollusca (117 species) the percentages for species of the dominating taxa
were: Mitridae 15%, Cerithidae 11 %, Conidae 10%, Muricidae and related
taxa 8%, Cypraeidae 7%, Terebridae 6%, Strombiidae 4%. But as regards
the total number of specimens (not counting the micromolluscs) the
Cypraeidae were most numerous (52%) followed by Cerithiidae with 16%,
Terebridae 4%, and Mitridae 2%. Five dominating species alone formed
75% of the total number of Mollusca. These were: Cypraea oblevata,
Cerithium piperitum, Strombus mutabilis, Terebra sp., and Vermetus
maximus. Three species out of 117 were responsible for 90% of the total
molluscan biomass: Vermetus maximus, Tridacna maxima and Cypraea
obleviata. In the coastal lagoon of the same barrier reef, the bottom of
which was covered by sand with the admixture of detritus and with rear
corals, just the one Cypraea obleviata comprised 60% of the total numer of
species. The number of this gastropod exceeded 100 sp. m- 2 . Other
dominating species in this biotope were: Cerithium piperum, Strombus
mutabilis, Cantharus fumosus, C. coronatum, and Pyramidella sp.
The density of communities, as a rule, drastically varies in different areas
of the reef. Its maximum is usually in the littoral rocky biotopes and in the
wind-stressed reef edges. The vertical cliff slopes are most often densely
colonized by the bivalves, while their horizontal surfaces and the pools in