Can passive recruitment explain harpacticoid copepod distributions in relation to epibenthic structure?

Abstract

The importance of epibenthic structure and food in determining harpacticoid copepod densities was examined. Short-term recruitment of total harpacticoids, harpacticoid nauplii, Harpacticus spp., Tachidius triangularis Shen & Tai, Huntemannia jadensis Poppe, and interstitial harpacticoids into paired, defaunated sediment containers with mimic marsh grass or no structure was monitored in three field experiments. Although few statistically significant recruitment differences between these treatments were found, there was a general pattern of higher recruitment into one type of treatment for each experiment. In the first two experiments, higher abundances were usually found in the no-structure member of a treatment pair. These results matched those of a flume study in which less particulate matter accumulated within an area with structure compared to structureless areas. In the third experiment, the pattern was reversed. Trends in harpacticoid colonization among sampling periods were similar to that of bulk sediment transport. Harpacticoids responded positively to an enriched treatment created by allowing sediment containers to develop a rich microbial flora prior to deployment in the field, compared to an unenriched treatment. This positive response suggests that behavior can be important in determining local harpacticoid abundance. We conclude that passive recruitment alone cannot explain small-scale spatial distributions of harpacticoids.