STOCHASTIC EVENTS AND DYNAMICS OF A MANGROVE ROOT EPIFAUNAL COMMUNITY

Submerged roots of red mangroves (Rhizophora mangle) in the Florida Keys were photographed at 1- or 2-month intervals for 38 months to measure population dynamics of the epifaunal invertebrate species. Photographs were analysed for species composition and abundance and information on life spans, persistence, mortality, and seasonality. Larval recruitment to artificial surfaces was used to assess reproductive seasonality. As a measure of stability, populations were tested for narrow stochastic boundedness. In contrast to reports for a tropical mangrove root community, the Florida Keys root community showed enormous variability despite being dominated by long-lived species with low, largely nonseasonal recruitment. Species composition on individual roots changed dramatically on short time scales. Populations of the major species were not narrowly bounded on most roots and there was little evidence for a closely regulated community. Variability of this community related to the frequency and intensity of stochastic perturbations. Physical disturbance due to strong tidal flows appeared to be the most important structuring process. Species-specific predation and fragmentation of sponges were also important. These features contribute to the instability of the community by producing dramatic fluctuations in species abundances and preventing competitive processes from producing a more stable, equilibrium community. Temporal measurement scale was an additional important consideration in this habitat. Structuring processes occurred on very short time scales (1-2 months) and analysis on longer time scales gave inaccurate impressions of community dynamics.