Benthic Crustaceans
193
large colony of ramose coral Pocillopora or Acropora harbors 5 to 15
different species of symbiotic crustaceans, not to mention other infaunal
animals, such as sponges, molluscs, and polychaetes. The number of
specimens of crustaceans, shrimps and crabs in each such a coral colony
varies within 5 to 40. Among them are the pontionid, the alpheid, and the
hypolithid shrimps from the genera: Periclimenes, Philarius, Harpilopsis,
Fenneria, Corallicaris, ]ohaste, Thor, Hymenocera, Synalpheus, and
Alpheus. The infaunal symbiotic crabs belong most often to the xanthids
Chlorodiella, Phymodus, Cymo, Domecia, Trapezia (about 20 species) and
Tetralia (about 5 species). On the Caribbean reefs the infaunal crabs include
the spider crab Mitrax sp., some species of the family Porcellanidae, and the
crab Quadriella, which lives here on gorgonians (Castro 1976; Austin et al.
1980).
Three main groups can be named among the infaunal crustaceans. One of
them use the coral colony as a temporary refuge, which they casually
abandon, like the shrimp Periclimenes spiniferus and the crabs Phymodus
undulatus and Chlorodiella nigra, which often inhabit colonies of the coral
Pocillopora. The second group includes crabs and shrimps that live within
the colony permanently, but do not have any specific morphological
adaptations, which should distinguish them from their free-living relatives.
Those are the shrimps Periclimenes anymone, P. madreporae, Thor
amboinenses, and the crab Chlorodiella andreoussi. Both these groups of
infaunal crustaceans include species which feed independently of their host
corals, being filterers (shrimps) or feeding on mucus which the coral is
shedding anyway (crabs). The representatives of the third group are
specialized symbionts of corals. They have morphological adaptations for
using their hosts not only as a refuge but also as a source of food. Having
flattened bodies, they easily move between the coral's branches with the aid
of modified legs fit for climbing over their slimy surfaces. At the end of their
hind feet they have special "brushes" and "combs". Lacerating the polyps
of corals with the combs, the crabs stimulate mucus excretion and then
collects this mucus with the "brushes" and eats it (Bruce 1976). This
symbiosis is mutualistic because the crustacean symbionts defend their hosts
against the attacks of corallavorous predators (Abele and Patton 1976;
Glynn 1983), as well as against the settling of the larvae of borers on the
host colony. They also clean the surfaces of the colony from excess mucus
and sediments. They feed only on their host's resources, eating not only
mucus and zooxanthellae of the host coral, but also the tissues of coenosarc,
and even snatching off the preys caught by its polyps. The symbiotic crabs
form permanent couples. In one individual coral colony usually only one
couple of a given species lives, which repel other crabs of the same species.
The crab Hapalocarcinus and the shrimp Paratypton can control the growth
of some branching corals. On their branches they form chambers in which
their caged females live (Patton 1976). Their larvae settle on the tip of a
growing branch, influencing then its growth so that the growing branch
193
large colony of ramose coral Pocillopora or Acropora harbors 5 to 15
different species of symbiotic crustaceans, not to mention other infaunal
animals, such as sponges, molluscs, and polychaetes. The number of
specimens of crustaceans, shrimps and crabs in each such a coral colony
varies within 5 to 40. Among them are the pontionid, the alpheid, and the
hypolithid shrimps from the genera: Periclimenes, Philarius, Harpilopsis,
Fenneria, Corallicaris, ]ohaste, Thor, Hymenocera, Synalpheus, and
Alpheus. The infaunal symbiotic crabs belong most often to the xanthids
Chlorodiella, Phymodus, Cymo, Domecia, Trapezia (about 20 species) and
Tetralia (about 5 species). On the Caribbean reefs the infaunal crabs include
the spider crab Mitrax sp., some species of the family Porcellanidae, and the
crab Quadriella, which lives here on gorgonians (Castro 1976; Austin et al.
1980).
Three main groups can be named among the infaunal crustaceans. One of
them use the coral colony as a temporary refuge, which they casually
abandon, like the shrimp Periclimenes spiniferus and the crabs Phymodus
undulatus and Chlorodiella nigra, which often inhabit colonies of the coral
Pocillopora. The second group includes crabs and shrimps that live within
the colony permanently, but do not have any specific morphological
adaptations, which should distinguish them from their free-living relatives.
Those are the shrimps Periclimenes anymone, P. madreporae, Thor
amboinenses, and the crab Chlorodiella andreoussi. Both these groups of
infaunal crustaceans include species which feed independently of their host
corals, being filterers (shrimps) or feeding on mucus which the coral is
shedding anyway (crabs). The representatives of the third group are
specialized symbionts of corals. They have morphological adaptations for
using their hosts not only as a refuge but also as a source of food. Having
flattened bodies, they easily move between the coral's branches with the aid
of modified legs fit for climbing over their slimy surfaces. At the end of their
hind feet they have special "brushes" and "combs". Lacerating the polyps
of corals with the combs, the crabs stimulate mucus excretion and then
collects this mucus with the "brushes" and eats it (Bruce 1976). This
symbiosis is mutualistic because the crustacean symbionts defend their hosts
against the attacks of corallavorous predators (Abele and Patton 1976;
Glynn 1983), as well as against the settling of the larvae of borers on the
host colony. They also clean the surfaces of the colony from excess mucus
and sediments. They feed only on their host's resources, eating not only
mucus and zooxanthellae of the host coral, but also the tissues of coenosarc,
and even snatching off the preys caught by its polyps. The symbiotic crabs
form permanent couples. In one individual coral colony usually only one
couple of a given species lives, which repel other crabs of the same species.
The crab Hapalocarcinus and the shrimp Paratypton can control the growth
of some branching corals. On their branches they form chambers in which
their caged females live (Patton 1976). Their larvae settle on the tip of a
growing branch, influencing then its growth so that the growing branch