188
Reef Zoo benthos
benthos of the soft sediments, especially in the littoral zone of barrier and
fringing reefs. But their numbers even there are usually rather low: 50-200
sp. dm 3 of sediment. This is an order less than those of the nematods. In
areas of silty or of oxygen-poor sediments near big islands the importance of
oligochaetes largely increases (Thomassin et al. 1982).
The round worms nematods are frequent in reef bottom sediments
(Renaud-Morn ant et al. 1971; Thomassin et al. 1976; Grelet 1985). Their
size is 0.2-1 mm and an individual weighs only 3-10 Ilg. The number of
nematods in coral sands varies within 0.2 to 2 x 10 6 sp. m- 2 , thus they
comprise a significant part of the microbenthos, attaining a level of biomass
of 1 to lOgm- 2 • Most of them are sediment- or detritus-feeders, but some
of their species are predatory. The nematods themselves are an important
source of food for various benthic fauna and fish (Salvat and RenantMornant 1969).
The reef ribbon worms nemeretins are ordinarily present in the infaunal
benthos. They live under stones, in trenches, and in coral rubble. Some of
them could be very long - up to 1 m and more (Baseodiscus). Their other
common genera have sizes from 1 cm (Poseidonemeretis) to 5 -10 cm
(Gorgonorhynchus, Nemerites). Most of nemeretine worms are predators.
Small nemeretines often comprise a significant part of the meiobenthos
(Gibson 1982; Devaney et al. 1987).
The flat worms turbellarians are mostly commensals of corals and
sponges. Some of their species are criptofaunal. Most of turbellarians have
sizes of 1-5 cm and a very diverse and bright coloration. Taxonomically they
are represented in reef benthos by the genera Pseudoceros, Stychoplana,
Paraplanocera (order Polycladia).
5.4 Benthic Crustaceans
5.4.1 Community Structure
Reef crustaceans are one of the most diverse and abundant groups of the
coral reef vagile and sedentary benthos. Various of their taxa occupy
numerous trophical niches in bottom reef biotopes, thus providing efficient
use of the food sources within the benthic communities. Hundreds of species
of crustaceans are commensals, symbionts or parasites of sessile and vagile
benthic and planktonic reef animals. Many of their species are criptofaunal.
The total number of crustacean species on the reefs of the Indo-Pacific
exceeds 1200, including ca. 800 species of decapods, of which 500 species are
crabs (Serene 1972; Haig 1976). Among the communities of the reef crustaceans their following ecological groups could be named: (1) the demersal
crustaceans, which at night swim in the water column and in the daytime
hide in bottom sediments, rubble, seaweeds, and perforated reef rocks, thus
Reef Zoo benthos
benthos of the soft sediments, especially in the littoral zone of barrier and
fringing reefs. But their numbers even there are usually rather low: 50-200
sp. dm 3 of sediment. This is an order less than those of the nematods. In
areas of silty or of oxygen-poor sediments near big islands the importance of
oligochaetes largely increases (Thomassin et al. 1982).
The round worms nematods are frequent in reef bottom sediments
(Renaud-Morn ant et al. 1971; Thomassin et al. 1976; Grelet 1985). Their
size is 0.2-1 mm and an individual weighs only 3-10 Ilg. The number of
nematods in coral sands varies within 0.2 to 2 x 10 6 sp. m- 2 , thus they
comprise a significant part of the microbenthos, attaining a level of biomass
of 1 to lOgm- 2 • Most of them are sediment- or detritus-feeders, but some
of their species are predatory. The nematods themselves are an important
source of food for various benthic fauna and fish (Salvat and RenantMornant 1969).
The reef ribbon worms nemeretins are ordinarily present in the infaunal
benthos. They live under stones, in trenches, and in coral rubble. Some of
them could be very long - up to 1 m and more (Baseodiscus). Their other
common genera have sizes from 1 cm (Poseidonemeretis) to 5 -10 cm
(Gorgonorhynchus, Nemerites). Most of nemeretine worms are predators.
Small nemeretines often comprise a significant part of the meiobenthos
(Gibson 1982; Devaney et al. 1987).
The flat worms turbellarians are mostly commensals of corals and
sponges. Some of their species are criptofaunal. Most of turbellarians have
sizes of 1-5 cm and a very diverse and bright coloration. Taxonomically they
are represented in reef benthos by the genera Pseudoceros, Stychoplana,
Paraplanocera (order Polycladia).
5.4 Benthic Crustaceans
5.4.1 Community Structure
Reef crustaceans are one of the most diverse and abundant groups of the
coral reef vagile and sedentary benthos. Various of their taxa occupy
numerous trophical niches in bottom reef biotopes, thus providing efficient
use of the food sources within the benthic communities. Hundreds of species
of crustaceans are commensals, symbionts or parasites of sessile and vagile
benthic and planktonic reef animals. Many of their species are criptofaunal.
The total number of crustacean species on the reefs of the Indo-Pacific
exceeds 1200, including ca. 800 species of decapods, of which 500 species are
crabs (Serene 1972; Haig 1976). Among the communities of the reef crustaceans their following ecological groups could be named: (1) the demersal
crustaceans, which at night swim in the water column and in the daytime
hide in bottom sediments, rubble, seaweeds, and perforated reef rocks, thus