Resource utilization and competition among the five Hawaiian species of Trapezia (Crustacea, Brachyura)

Abstract

Crabs of the genus Trapezia and their hosts, the reef corals Pocillopora spp., were collected at 2 sites on the island of Oahu, Hawaii. At one site, Kahe Point, all 5 Hawaiian species of Trapezia were common, while at Kaneohe Bay, the other site, only T. intermedia and T digifafis were abundant More than 90 % of corals at both sites were inhabited by at least 1 species of Trapezia. Crabs usually occurred as heterosexual pairs, with a single pair of a glven specles per coral head. Up to 5 species were found to CO-occur on single coral colonies. T. intermedia is abundant on coral colonies of all sizes, but the other species of Trapezia are largely restricted to colonies larger than 2000 to 4000 cm3, probably as a result of their aggressive exclusion from small colonies by T intermedia. fistograms of host size frequency do not support a previous worker's conclusion that Hawailan species of Trapezia segregate the host coral resource according to colony size. Log-linear analysis of species cooccurrence frequencies shows no significant interactions among species except In small colonies. It is hypothesized that territory size exceeds that needed to supply a crab pair's resource requirements. Strong intraspecific territoriality, and a reduction of interspec~f~c territoriality, may allow the coexistence of competing species of Trapezia even if there is overlapping resource utilizahon.