Bacterial suspension feeding by coral reef benthic organisms

The linkage between the pelagic microbial loop in coral reefs and reef benthic communities needs study in view of changing characteristics of tropical coastal seas. We conducted field experiments, using standard microbial techniques, to assess the uptake of natural water-borne bacteria (at natural densities, 0.4 to 0.6 x 10(6) cm(-3)) by 2 common Caribbean reef organisms, the scleractinian coral Madracis mirabilis and the colonial ascidian Trididemnum solidum. The data show that these organisms are effective bacterial suspension feeders. Feeding rates of 0.75 to 1.07 x 10(9) bacterial cells 100 cm(-2) h(-1) translate into a nitrogen input of 3 to 4 nmol N cm(-2) h(-1). These values indicate that a large part of the nitrogen derived from particulate sources could be supplied by bacteria. We suggest that such efficient linkage between these reef organisms and the pelagic microbial communities explains the increasing/continued abundance of such benthic organisms on deteriorating Caribbean reefs.