RECRUITMENT OF SESSILE MARINE INVERTEBRATES ON HAWAIIAN MACROPHYTES: DO PRE-SETTLEMENT OR POST-SETTLEMENT PROCESSES KEEP PLANTS FREE FROM FOULING?

摘要

Although the polychaete Hydroides elegans and bryozoan Bugula neritina are dominant members of the fouling community in Hawaiian waters, these organisms were rarely found on macroalgae and seagrasses. Three explanations for this lack of fouling on mac-rophytes were considered: (1) larvae did not settle on these surfaces, (2) physical characteristics of the macrophytes prevented firm attachment, and (3) macrophyte flexibility exceeded animal flexibility. To determine if either invertebrate would settle on 40 species of macrophytes, settlement bioassays were run. When exposure was toxic to larvae, chemical anti-fouling mechanisms were suggested. Macrophytes that were not toxic, but avoided by settling larvae, may have been chemically protected by non-toxic, deterrent compounds, or avoided because of unacceptable morphologies or surface energies. When larval settlement occurred, adhesion strength was tested. To determine if macrophytes were more flexible than attached invertebrates, the macrophyte with attached animals was bent around rods of decreasing diameter until animals were dislodged, or the lamina broke. One or more of the tested types of anti-fouling protection could explain the lack of H. elegans on all 40 macrophytes. Pre-settlement defenses explained the lack of H. elegans on 23 species; post-settlement processes could explain its absence on the remaining 17 species. The lack of B. neritina could only be explained on 18 species of macrophytes.