Some Determinants of the Composition and Abundance of Motile Macroinvertebrate Species in Tropical and Temperate Turtlegrass (Thalassia testudinum) Meadows

Abstract

Monthly data on motile epibenthic macroinvertebrates inhabiting subtidal tropical (Panama') and warm temperate (U.S.A.) turtlegrass (Thalassia testudinum) meadows were gathered to test the hypothesis that structurally similar habitats will support similar numbers of species, regardless of latitude. Taken at face value these data do not support the hypothesis; species richness was significantly greater in Panama'. However, based on observational evidence as well as previously published natural history information it appears that the Panamanian sea grass meadows are effectively more structurally complex than those in Florida. This is primarily due to the presence of nearby coral reefs which support several invertebrate and many fish species which treat the coral reef - seagrass habitat as a single entity. In addition, many more vagrant species were taken in the tropical collections, as a result of the proximity of many other distinct habitats in Panama. Differences in total macroinvertebrate abundance between the two study areas seem to reflect differences in seasonal fluctuations of their fish predators, and in the species composition and biological activities of the fishes themselves. The predation and disturbance hypotheses can also be advanced to explain the results of this study. Although neither one of them seems to be correct, both are compatible with the data presented here. This suggests caution in accepting the mechanisms implied by hypotheses making very general predictions on community organization, when no independent information exists to verify them.