Effects of Refuges and Recruitment on Gonodactylid Stomatopods, a Guild of Mobile Prey

Postlarval recruitment and features of the habitat, especially the availability of spatial refuges, were examined for their effect on the abundance of gonodactylid stomatopods along the Caribbean coast of Panama. Gonodactylus bredini, Gonodactylus oerstedii and Gonodactylus austrinus occupied and aggressively defended cavities in coral rubble as refuges from predators throughout an intertidal bed of turtlegrass, Thalassia testudinum. Although water height, Thalassia density, and rubble density all varied significantly within the habitat, variation in the local density of gonodactylids was related only to the density of coral rubble. Manipulation of rubble showed that any change in the abundance of rubble, either positive or negative, altered local densities of gonodactylids in the same manner. Cavities within the rubble, however, provided the true, potentially limiting microenvironment. Comparisons between gonodactylid densities and cavity densities showed that the number of cavities limited the local densities of individuals. However, noncontinuous and variable postlarval recruitment created temporal variation in the abundances of smaller gonodactylids and sometimes limited their densities below the capacity of their cavities. The impact of cavities, therefore, depended on the size of the individual and the recent history of postlarval recruitment. Nonuniform resource utilization and nonuniform resource abundance allowed both the shortage of necessary resource and the restricted time when the population's rate of increase was positive to limit the number of individuals simultaneously. Although the spatial distribution of cavities affected the availability of cavities and lowered the effective supply of refuges, its effect on gonodactylid densities was unclear. The inaccessibility of cavities most likely affects gonoacytlids qualitatively by contributing to the maintenance of aggression in these populations.