Bacterial suspension feeding by coral reef benthic organisms

The linkage between the pelagic microbial loop in coral reefs and reef bent hic communities needs study in view of changing characteristics of tropical coastal seas. We conducted field experiments, using standard microbial tec hniques, to assess the uptake of natural water-borne bacteria (at natural d ensities, 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 Tridid emnum solidum. The data show that these organisms are effective bacterial s uspension feeders. Feeding rates of 0.75 to 1.07 x 10(9) bacterial cells 10 0 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 par ticulate sources could be supplied by bacteria. We suggest that such effici ent linkage between these reef organisms and the pelagic microbial communit ies explains the increasing/continued abundance of such benthic organisms o n deteriorating Caribbean reefs.