Complex trophic and nontrophic interactions between meiobenthic copepods and marine snow

Abstract

Trophic and nontrophic interactions between sediment-associated metazoans and marine snow (organic aggregates ca. 0.5 mm in diameter) in the water column represent an unexplored potential link between benthic and pelagic environments. To investigate the possibility that such a link exists, we examined the effects of meiobenthic harpacticoid copepod assemblages on the formation and development of laboratory-generated marine snow. Known densities of a mixed-species copepod assemblage collected from Spartina alterniflora Loisel stems were added to rotating cylinders filled with 63 μm filtered natural seawater collected from a tidal creek on Sapelo Island, GA, USA. Copepod effects on aggregate numbers, aggregate volume and nonaggregate and aggregate total particulate matter (TPM), total particulate carbon (TPC), and bacterial densities were determined after 18 h. Aggregate numbers declined and aggregate volume increased significantly in the presence of as few as 4 copepods 1 −1. The presence of copepods produced larger, less-dense aggregates in contrast to expected animal grazing effects on marine snow. Changes in TPM were inconsistent and ranged from no difference in nonaggregate amounts between treatments to an ca. 50% decrease in aggregate amounts with increased copepod density. Treatment level differences in both nonaggregate or aggregate TPC could not be attributed to a copepod effect. Copepod activities produced either a decrease in the concentration of bacteria or aggregates or a decrease in both nonaggregate and aggregate bacterial densities. Although results do not allow us to conclude which mechanisms generate the observed copepod effects on marine snow, experiments indicate that benthic copepods in the water column can affect significantly the physical and biological dynamics of marine snow aggregates in shallow coastal systems.