196
Reef Zoobenthos
coral sand, feed on forams, microbenthic molluscs and worms, and also on
the microphytobenthos. The daily food ration of urchin communities in the
littoral area of an Atlantic reef appeared to be very large: 1-4 g m -2, e.g.,
1-6% of their body weight or 20-80% of a benthic plant's primary
production (Ogden 1977; Hatcher 1983b).
The families of the diademid urchins and of the relative tripneustid
urchins inlude the most common widespread genera Diadema, Astropyga,
Echinotrix, Temnopleurus, Mespilia, Toxopneustes, Tripneustes, Nudechinus.
At the Indo-Pacific reefs the most numerous species are Diadema setosum,
D. savignyi, Tripneustes pileosus, T. gratilla, Echinothrix diadema, and E.
calamaris. On the Caribbean reefs they are: Diadema antillarum, Astropyga
radiata, A. magnifica, Echinothrix calamaris, Tripneustes ventricosa (Endean
1957; Clark 1976; Budin 1980; Marsh and Marshall 1983). Some mass
species of regular urchins belong to other two families: Echinometridae and
Sidaridae. These are: on reefs of the Indo-Pacific Echinometra mathaei,
E. oblonga, Echinostrephus aclilulatus, E. molaris, Heterocentrotus mammilaris, H. trigonarius, Eucidaris metularia, E. thouarsii, and in the Western
Atlantic reefs Echinometra lucunter, E. viridis, and Eusidaris tribuloides.
The heterocentrotuses or pencil urchins have massive and extremely firm
needles, which they use for boring holes in reef-flat rocks.
The irregular clypeasterid urchins and the heart-like brissid urchins have
flat bodies densely covered with fine short needles. The flat body enable
them to move freely inside the sediments. The common species of clypeasterid urchins on the Atlantic reefs are: Clypeaster rosaceus, Encope stockesi,
Leodia sp., Mellita quinquesperforata, and Echinoneus cyclostomus. The
latter and also Clypeaster reticulatus, C. fervens, and Echinodiscus bisperforatus are the most numerous also on the Indo-Pacific reefs. The mass
species of heart-like urchins on the Atlantic reefs are: Plagiobrissus grandis
and Meoma ventricosa, and in the Indo-Pacific: Metalia spatagus, M.
sternalis, M. dicrana, Brissus latecarinatus, and Rhinobrissus hemiasteroides.
These urchins often form very dense monospecific populations on the sandy
bottom of lagoons, where 10-20 large urchins m- 2 (Budin 1980) can be
found. On sands covered with sea-grass it could be even more - up to
200 sp. m- 2 (Fadeev and Lukin 1987).
The poisonous sharp needles defending the urchins' bodies nevertheless
cannot prevent their being grazed by some specialized predators. They are
eaten by diodontid and balistid fish which are steadily regulating their
population densities (Ormond et al. 1989). The urchins are grazed also by
large predatory gastropods (Cassis), by crabs and lobsters. The urchins,
especially the diademids, consume large quantities of seaweeds, coral spat
and the corals themselves, thus influencing the development and
composition of whole reef benthic communities (Bak and van Eys 1975;
Benayahu and Loya 1977; Ogden and Lobel 1978; Williams 1981; Sammarco
1982; Huges et al. 1987; Bak 1989).
Reef Zoobenthos
coral sand, feed on forams, microbenthic molluscs and worms, and also on
the microphytobenthos. The daily food ration of urchin communities in the
littoral area of an Atlantic reef appeared to be very large: 1-4 g m -2, e.g.,
1-6% of their body weight or 20-80% of a benthic plant's primary
production (Ogden 1977; Hatcher 1983b).
The families of the diademid urchins and of the relative tripneustid
urchins inlude the most common widespread genera Diadema, Astropyga,
Echinotrix, Temnopleurus, Mespilia, Toxopneustes, Tripneustes, Nudechinus.
At the Indo-Pacific reefs the most numerous species are Diadema setosum,
D. savignyi, Tripneustes pileosus, T. gratilla, Echinothrix diadema, and E.
calamaris. On the Caribbean reefs they are: Diadema antillarum, Astropyga
radiata, A. magnifica, Echinothrix calamaris, Tripneustes ventricosa (Endean
1957; Clark 1976; Budin 1980; Marsh and Marshall 1983). Some mass
species of regular urchins belong to other two families: Echinometridae and
Sidaridae. These are: on reefs of the Indo-Pacific Echinometra mathaei,
E. oblonga, Echinostrephus aclilulatus, E. molaris, Heterocentrotus mammilaris, H. trigonarius, Eucidaris metularia, E. thouarsii, and in the Western
Atlantic reefs Echinometra lucunter, E. viridis, and Eusidaris tribuloides.
The heterocentrotuses or pencil urchins have massive and extremely firm
needles, which they use for boring holes in reef-flat rocks.
The irregular clypeasterid urchins and the heart-like brissid urchins have
flat bodies densely covered with fine short needles. The flat body enable
them to move freely inside the sediments. The common species of clypeasterid urchins on the Atlantic reefs are: Clypeaster rosaceus, Encope stockesi,
Leodia sp., Mellita quinquesperforata, and Echinoneus cyclostomus. The
latter and also Clypeaster reticulatus, C. fervens, and Echinodiscus bisperforatus are the most numerous also on the Indo-Pacific reefs. The mass
species of heart-like urchins on the Atlantic reefs are: Plagiobrissus grandis
and Meoma ventricosa, and in the Indo-Pacific: Metalia spatagus, M.
sternalis, M. dicrana, Brissus latecarinatus, and Rhinobrissus hemiasteroides.
These urchins often form very dense monospecific populations on the sandy
bottom of lagoons, where 10-20 large urchins m- 2 (Budin 1980) can be
found. On sands covered with sea-grass it could be even more - up to
200 sp. m- 2 (Fadeev and Lukin 1987).
The poisonous sharp needles defending the urchins' bodies nevertheless
cannot prevent their being grazed by some specialized predators. They are
eaten by diodontid and balistid fish which are steadily regulating their
population densities (Ormond et al. 1989). The urchins are grazed also by
large predatory gastropods (Cassis), by crabs and lobsters. The urchins,
especially the diademids, consume large quantities of seaweeds, coral spat
and the corals themselves, thus influencing the development and
composition of whole reef benthic communities (Bak and van Eys 1975;
Benayahu and Loya 1977; Ogden and Lobel 1978; Williams 1981; Sammarco
1982; Huges et al. 1987; Bak 1989).