PERMEABILITY OF PATCH BOUNDARIES TO BENTHIC INVERTEBRATES - INFLUENCES OF BOUNDARY CONTRAST, LIGHT LEVEL, AND FAUNAL DENSITY AND MOBILITY

This study empirically examines predictions concerning boundary permea bility as a function of patch contrast (i.e., the magnitude of differe nce in measures across patch interfaces). light level, and faunal mobi lity and density, as well as relative rates of emigration and immigrat ion. I assessed permeability using invertebrate transfer in a macroalg al-seagrass-sand landscape, with particular emphasis on the caridean s hrimp Thor floridanus. Proportional emigration was estimated by staini ng algal fauna in situ using neutral red (a live immersion stain) and then later collecting all animals in the algal clumps and in the surro unding sand or seagrass. Permeability was in part a function of bounda ry contrast in this milieu; macroalgal patches were more of a closed s ystem in sand than in seagrass. Contrary to predictions, proportional emigration across both the algal-seagrass and algal-sand boundaries wa s inversely related to faunal density. Another unexpected result was t hat the rate of change in emigration with increasing density was unaff ected by differential contrast among habitat types The observed enhanc ed permeability for mole motile fauna was consistent with predictions. A related finding was that permeability was greater at night than dur ing the day, probably as a function of increased nocturnal vagility of benthic fauna. Emigration was not in equilibrium with immigration at the temporal scale of this study (hours) for the majority of species t ested. Emigration-immigration disequilibria should be most likely when the temporal scale is small, and in such cases caution should be exer cised when extrapolating from one transfer parameter to the other.