INTERACTIONS WITH THE BENTHOS ALTER PELAGIC FOOD WEB STRUCTURE IN COASTAL WATERS

Results from studies in experimental enclosures containing both water column and benthic communities show that the benthos has an important effect on the structure and productivity of pelagic food webs whether the system is nutrient enriched or nutrient limited. Research over a 10-yr period in 13-m3 mesocosms showed that changes in the pelagic food web were correlated with different sediment communities and with the presence or absence of a benthos. The abundance of copepods was inversely correlated with numbers of macrofauna. At both low and high nutrient levels, systems without benthos had greatly enhanced numbers of carnivorous holozooplankton including ctenophores, medusans, chaetognaths, and fish. Our observations indicate that the presence of the benthos shortens the pelagic food web and inhibits the response of pelagic fauna to nutrient enrichment in well-mixed coastal waters. The strength of benthic-pelagic coupling, which is controlled by the amount of turbulence in the water column, may be more important to food web structure than the rate of nutrient supply and could determine which subsystem responds to eutrophication.