Macrobenthic Invertebrates in Bare Sand and Seagrass (Thalassia testudinum) at Carrie Bow Cay, Belize

摘要

The generally accepted view that seagrasses support a more dense and diverse invertebrate fauna than sand areas devoid of such vegetation was tested in Thalassia testudinum beds of Carrie Bow Cay lagoon, Belize. Mechanisms regulating the distribution of invertebrates were also examined. Core samples from five stations, ranging from bare sand to dense seagrass, indicated no clearcut effect of seagrass versus bare sand on densities of polychaetes and mollusks. The numbers of species from all seagrass stations were not significantly higher than those from sand stations. Species diversities for all stations were influenced mainly by species richness, except for the station in dense seagrass where species evenness was high. The most abundant polychaete and mollusk species sampled were found at all stations. The proportion of fine-grained sediments in the substrate increased progressively from bare sand into the seagrass. Encrusting coralline algae provide a major contribution to the fine sediments of the grass beds. Seagrass standing crop increased from the small seagrass patch to the dense Thalassia bed. Inorganic components made up 49% of live and 70% of dead seagrass. This study found no relationship between seagrass standing crop and species densities of invertebrates. Intense predation pressure is proposed as the primary regulating mechanism of species densities in the Carrie Bow lagoon. Experimental field studies are needed to clarify predator-prey interactions.