Coral-crab association: a compact domain of a multilevel trophic system

Colonies of the Red Sea branching coral Stylophora pistillata were incubated in situ with radioactive carbon and Trapezia cymodoce crabs were introduced to the colonies, for one month each, up to 7 months after coral labelling. Zooxanthellar photosynthetic products were translocated to the crabs via host coral tissue. Based upon crab/coral tissue conversion from 53 crab samples, crabs possessed radioactive material equal to that recorded in 320-770 mm² of coral tissue (up to 2257 mm²). This material was translocated mainly by direct 'grazing' on coral tissue rather than mucus collection. Ovigerous female crabs (39 specimens) accumulated significantly more labelled carbon than males, and up to 53 % of their radioactivity was concentrated in their reproductive organs. A pair of crabs dwelling in a coral colony consumed ca 130 cm² of host tissue per month (40-45 cm length of coral branches). This system represents a compact, obligatory multilevel trophic domain which also radiates horizontally by allocation of energy derived from algal photosynthesis into planula and zooea larva production, permitting the development of long trophic chains and a complex food web.