COMMUNITY INTERACTIONS OF CAPRELLA PENANTIS LEACH (CRUSTACEA: AMPHIPODA) ON SEA WHIPS

Sea whips, Leptogorgia virgulata L., occurring in Thalassia testudinum (Konig) meadows in northwestern Florida support an epifaunal community which is dominated by the caprellid amphipod Caprella penantis Leach. Caprella penantis densities were 23 times greater when T. testudinum died back during the winter than when T. testudinum was more dense. Observations made during seasonal collections indicate that most fish predators of C. penantis are absent during the winter. Caprella penantis densities may have been decreased by fish predation, but the density increases were due to reproductive output. When C. penantis densities on sea whips decreased, postlarval and juvenile decapod crustaceans colonized the sea whip. The reptantians remained on the sea whips through several molts and then dropped from the sea whips to join the benthic macrofaunal community. Epibiotic communities, therefore, have been demonstrated to be involved in at least three important marine ecosystems processes: (1) they serve as a concentrated and recognizable food source for nekton, (2) epibionts graze periphyton and detritus from the biotic substratum, thereby preventing smothering, and (3) some benthic invertebrates temporarily join the epibiotic community during their transition from planktonic to epibenthic life styles. Sessile and sedentary marine macroscopic organisms are common features of marine and estuarine environments, and these organisms act as a substratum for numerous epibiotic organisms (Coe, 1937; Colman, 1939; Dahl, 1948). Dean (1981) correlates species diversity of these epibiotic communities with the structural complexity of the sessile community. He attributes the positive relationship to specific habitat preferences by the epibionts. Logic supports Dean's (1981) suggestion because habitat selectivity by the epibionts is generally attributed to food availability and camouflage (Nagle, 1968; Keith, 1971; Hughes, 1978; Caine, 1979a, 1980). When confined to consideration of fouling organisms that have similar morphology, Dean's (1981) hypothesis also suggests the possible presence of parallel epibiotic communities. Comparison of epibiotic communities of sea grasses indicates that the epibiotic communities are parallel, regardless of the sea grass species (Kikuchi, 1966; Ledoyer, 1966, 1969; Nagle, 1968; Kikuchi and Peres, 1977). Thorson (1955) postulated that parallel communities should function similarly, with analogous species conducting similar activities. The global presence of analogous communities may also indicate similar interactions of the epibiotic communities with their biotic substrata and within their ecosystem. Caprellid amphipods are ubiquitous epibionts which frequently are numerically dominant within epibiotic communities. Studies conducted in Puget Sound, Washington (U.S.A.), which concentrated on activities of caprellid amphipods of the genus Caprella, showed that: (1) sea grass epibionts serve as a food source for surrounding benthic and pelagic communities, especially for juvenile fish, i.e., as nursery grounds (Caine, 1979a), and (2) some epibionts (e.g., Caprella laeviuscula), may remove fouling organisms and detritus from the biotic substratum, thereby preventing smothering of the substratum (Caine, 1980). In this paper I report on activities and community interactions of Caprella penantis Leach from the gorgonian Leptogorgia virgulata L. in northwestern Florida (Gulf of Mexico). My focus was to determine the applicability of the Puget Sound generalities to distant communities.