Sponges
173
them are inhabited by medium-sixed gastropods (Nerita, Area, Cerithium,
Littorina, chitons), which number up to hundreds per square meter.
Therefore, the biomass of molluscs may reach in these biotopes up to
several kgm- 2 (Grassle 1973; Gulbin et al. 1987). On the reef flat and the
sand bottom of the lagoon the number of macro benthic molluscs varies
within 3-20 sp. m- 2 and their biomass within 5-50 gm- 2 (Salvat 1972;
Ricard 1981). An average molluscan biomass in the lagoon of the Takapoto
atoll was around 5 g m -2. But actually these numbers could be underestimates because of the missing micromolluscs, the biomass of which in soft
reef sediments might be at the same level as that of macro benthic species
(Hutchings 1974). Many species of molluscs are fished on reefs for food,
souvenirs, collections and the handicrafts. Among them are: Haliotis,
Mytilus, Pecten, Cardium, Littorina, Tridacna, Pinna, oysters, venerids and
pteriids.
5.2 Sponges
5.2.1 Features of Morphology and Physiology; Symbiosis
Sponges, as an element of the sessile benthos, are second in their importance after corals and zoantharians. Moreover; the function of sponges in the
coral reef ecosystem is somewhat similar to the function of the corals
themselves. Many sponges have algal symbionts, and thus they add to the
primary organic production. The calcareous sponges produce lime and take
part in reef-building processes cementing carbonaceous material during the
formation of reef-flat rocks. Scleropongia compose the framework constructions, thus functioning also as reef-builders, especially in deep zones of the
fore-reef, where the coral growth is weak (Hartman and Goreau 1970). The
spicule material produced by sponges is an important source for reef-bottom
sediments. The boring sponges also add to bottom sediments, being a main
agent of the bioerosion of reef-flat lime rocks (Goreau and Hartman 1963;
Thomas 1972; Hartman 1977).
Sponges are the most ancient and primitive among the multicellular
animals. Their tissues are not differentiated in edoderm and endoderm.
They are composed by groups of specialized cells. The motion of their
flagella is synchronized but each of the cells feeds independently . . The body
of a sponge is composed of the mesoglea - the structural substance
consisting of the fibers of collagen and spongin. The latter is a hornlike
structural material. The fibers of the mesoglea are framed by silicate or
calcareous spicules, which are taxonomically specific (Fig. 5.2). Outside, the
mesoglea is covered by a layer of the eptithelium-like flagellated cells - the
pinacoderm. The same layer of pinacoderm covers also the walls of
numerous channels furrowing the sponge's body. The flagella of pinacoderm
173
them are inhabited by medium-sixed gastropods (Nerita, Area, Cerithium,
Littorina, chitons), which number up to hundreds per square meter.
Therefore, the biomass of molluscs may reach in these biotopes up to
several kgm- 2 (Grassle 1973; Gulbin et al. 1987). On the reef flat and the
sand bottom of the lagoon the number of macro benthic molluscs varies
within 3-20 sp. m- 2 and their biomass within 5-50 gm- 2 (Salvat 1972;
Ricard 1981). An average molluscan biomass in the lagoon of the Takapoto
atoll was around 5 g m -2. But actually these numbers could be underestimates because of the missing micromolluscs, the biomass of which in soft
reef sediments might be at the same level as that of macro benthic species
(Hutchings 1974). Many species of molluscs are fished on reefs for food,
souvenirs, collections and the handicrafts. Among them are: Haliotis,
Mytilus, Pecten, Cardium, Littorina, Tridacna, Pinna, oysters, venerids and
pteriids.
5.2 Sponges
5.2.1 Features of Morphology and Physiology; Symbiosis
Sponges, as an element of the sessile benthos, are second in their importance after corals and zoantharians. Moreover; the function of sponges in the
coral reef ecosystem is somewhat similar to the function of the corals
themselves. Many sponges have algal symbionts, and thus they add to the
primary organic production. The calcareous sponges produce lime and take
part in reef-building processes cementing carbonaceous material during the
formation of reef-flat rocks. Scleropongia compose the framework constructions, thus functioning also as reef-builders, especially in deep zones of the
fore-reef, where the coral growth is weak (Hartman and Goreau 1970). The
spicule material produced by sponges is an important source for reef-bottom
sediments. The boring sponges also add to bottom sediments, being a main
agent of the bioerosion of reef-flat lime rocks (Goreau and Hartman 1963;
Thomas 1972; Hartman 1977).
Sponges are the most ancient and primitive among the multicellular
animals. Their tissues are not differentiated in edoderm and endoderm.
They are composed by groups of specialized cells. The motion of their
flagella is synchronized but each of the cells feeds independently . . The body
of a sponge is composed of the mesoglea - the structural substance
consisting of the fibers of collagen and spongin. The latter is a hornlike
structural material. The fibers of the mesoglea are framed by silicate or
calcareous spicules, which are taxonomically specific (Fig. 5.2). Outside, the
mesoglea is covered by a layer of the eptithelium-like flagellated cells - the
pinacoderm. The same layer of pinacoderm covers also the walls of
numerous channels furrowing the sponge's body. The flagella of pinacoderm