Reef Echinoderms
195
(holothurians). In the coral reef bottom biotopes these basic groups develop
great variety while displaying some features of endemism in particular reef
systems, such as the Caribbean or the Red Sea reef regions (Clark 1976). In
the Indo-Pacific region they include over 1000 species, and in the Western
Atlantic around 150, having only eight species common for these two
zoogeographic regions. Such segregation of the echinoderm faunas in these
regions is similar to the faunistic separation of their coral communities. The
endemism of the echinoderm fauna of coral reefs reveals also the fact that
out of 1027 of their species inhabiting reefs of the Indo-Pacific basin only 57
are common and could be found in it from one end to the other. Within a
single reef system the number of species of echinoderms varies within
20-150. Thus in the Red Sea it is 48, on the Caribbean reefs about 100, on
reefs of the Philippines 190, and on the Great Barrier Reef about 160
(Marsh and Marshall 1983).
The echinoderms often form dense monospecific populations in shallow
reef zones, which are an important component of the reef vagile macrobenthos and play an important role in trophodynamic and nutrients regeneration (Webb et al. 1977; Huges et al. 1987). The echinoderms produce
also a significant portion of lime material, thus functioning as reef builders.
They occupy all the trophic niches, as filterers (ophiuroids, crinoids),
detritus- and sediment-eaters (holothurians, ophiuroids), phytophages
(urchins) and predators (stars and, in part, urchins and ophiuroids).
5.5.1 Sea Urchins
The urchins inhabiting coral reefs belong to four main families:
Diadematidae, Ehinometridea (regular urchins), Clypeasteridae, Brissidae
(irregular urchins). The total number of urchin species on reefs of the
Indo-Pacific was evaluated with 140, while in particular reef systems it
varied within 10 to 40: on the Great Barrier reef 26 species, on the
Philippines 39. The density of their populations may attain 20-70 sp. m -3,
averaging 5 to 15 sp. m- I (Clark 1974; Budin 1980; Fadeev and Lukin 1987;
Bak 1989). Most reef urchins are nocturnal, hiding in the daytime in
trenches and holes. Some urchins (Echinometra, pencil urchin Heterocen
trotus) bore their holes themselves in reef lime rocks. The irregular urchins
dig into sand. Most urchins are omnivores. The regular urchins feed on
seaweeds and periphyton, consuming also young scleractinians, corals, and
microbenthos (Bak and van Eys 1975; Sammarco 1982; Hixon 1985).
Together with the periphyton and coralline algae they scrape off from the
flat surfaces also the spat of corals and small gastropodes. Some diadems
may feed also as sedimentary feeders from the water column. The organic
particles settling on their long needles covered with mucoid film are then
digested by the wandering amoebocytes, which crawl out from their porous
surfaces (Thomassin 1981). The irregular heart-like urchins, which live in
195
(holothurians). In the coral reef bottom biotopes these basic groups develop
great variety while displaying some features of endemism in particular reef
systems, such as the Caribbean or the Red Sea reef regions (Clark 1976). In
the Indo-Pacific region they include over 1000 species, and in the Western
Atlantic around 150, having only eight species common for these two
zoogeographic regions. Such segregation of the echinoderm faunas in these
regions is similar to the faunistic separation of their coral communities. The
endemism of the echinoderm fauna of coral reefs reveals also the fact that
out of 1027 of their species inhabiting reefs of the Indo-Pacific basin only 57
are common and could be found in it from one end to the other. Within a
single reef system the number of species of echinoderms varies within
20-150. Thus in the Red Sea it is 48, on the Caribbean reefs about 100, on
reefs of the Philippines 190, and on the Great Barrier Reef about 160
(Marsh and Marshall 1983).
The echinoderms often form dense monospecific populations in shallow
reef zones, which are an important component of the reef vagile macrobenthos and play an important role in trophodynamic and nutrients regeneration (Webb et al. 1977; Huges et al. 1987). The echinoderms produce
also a significant portion of lime material, thus functioning as reef builders.
They occupy all the trophic niches, as filterers (ophiuroids, crinoids),
detritus- and sediment-eaters (holothurians, ophiuroids), phytophages
(urchins) and predators (stars and, in part, urchins and ophiuroids).
5.5.1 Sea Urchins
The urchins inhabiting coral reefs belong to four main families:
Diadematidae, Ehinometridea (regular urchins), Clypeasteridae, Brissidae
(irregular urchins). The total number of urchin species on reefs of the
Indo-Pacific was evaluated with 140, while in particular reef systems it
varied within 10 to 40: on the Great Barrier reef 26 species, on the
Philippines 39. The density of their populations may attain 20-70 sp. m -3,
averaging 5 to 15 sp. m- I (Clark 1974; Budin 1980; Fadeev and Lukin 1987;
Bak 1989). Most reef urchins are nocturnal, hiding in the daytime in
trenches and holes. Some urchins (Echinometra, pencil urchin Heterocen
trotus) bore their holes themselves in reef lime rocks. The irregular urchins
dig into sand. Most urchins are omnivores. The regular urchins feed on
seaweeds and periphyton, consuming also young scleractinians, corals, and
microbenthos (Bak and van Eys 1975; Sammarco 1982; Hixon 1985).
Together with the periphyton and coralline algae they scrape off from the
flat surfaces also the spat of corals and small gastropodes. Some diadems
may feed also as sedimentary feeders from the water column. The organic
particles settling on their long needles covered with mucoid film are then
digested by the wandering amoebocytes, which crawl out from their porous
surfaces (Thomassin 1981). The irregular heart-like urchins, which live in