Biogeochemical Processes and Marine Benthic Community Structure: Which Follows Which?

Summary

Overall rates of decomposition in sediments appear to be only weakly affected by benthic animals. Thus we predict that changes in benthic community structure would have only a small effect on decomposition although the pathways of decomposition (aerobic vs. anaerobic) might shift. The converse does not appear to be true, however; we expect the structure of benthic communities to change with a change in decomposition rates, with some communities being excluded from sediments with high rates of decomposition.

In contrast, microalgal primary production in shallow benthic sediments may be strongly controlled by the animal community. In many systems, grazers completely consume the benthic algae for at least a portion of the year. We predict that the absence of grazers would have a dramatic effect on rates of primary production but we know less about the effect of the addition or loss of individual species in the benthic community. Large epibenthic animals have the largest effect on primary production in shallow systems whereas smaller infauna seem less able to deplete stocks of benthic microalgae.

There is some evidence that the structure of the animal community alters sulfur cycling in the sediments. In laboratory experiments, the partitioning between oxic metabolism and sulfate reduction shifts with the type of animal community. Sulfur burial over geologic time has decreased, perhaps due to the evolution of deeper burrowing organisms.

Finally, it appears that changes in benthic community structure have a large potential to alter nitrogen dynamics, especially inorganic nitrogen release and denitrification. Because the nitrogen cycle is closely linked with primary production and carbon loading to sediments, it provides a feedback mechanism between the fauna and other biogeochemical processes.