Recent work in deep-sea, soft-substratum communities suggests that species' abundances are strongly affected by processes at centimeter-to-millimeter scales and that many of these processes are governed by biologically produced structures (e.g., animal tubes). However, no mechanistic understanding of the role of such structures in deep-sea community dynamics has been obtained. Dr. Thistle and collaborator Dr. Eckman are evaluating mechanisms by which the 2-cm-diameter sediment concretions built by polychaetes affect harpacticoid copepod abundances in the San Diego Trough. In particular, their efforts will be focused on testing responses to fluid- and particle- dynamic effects of sediment concretions. They have used the submersible ALVIN to sample individual sediment concretions and bare areas of the sea floor and to initiate in situ experiments. They will complete analysis of samples, which were obtained in previous cruises. The analysis of these samples will enable the determination the importance of hydrodynamic and predation-refuge effects created by these structures. The former, in particular, are likely to be especially important in the deep ocean, because of the relatively low rates of physical disruption of sediments there. Further, sediment concretions are comparable in size to other widespread, deep-sea structures (e.g., ferromanganese nodules). generalizable.
