Abstract:
Descriptions of the rich sponge faunas inhabiting mangrove roots at various
Caribbean sites are unanimous in pointing out the heterogeneity of species distribution
and abundance patterns at all scales, from different portions of a single root to geographic
subregions. Abiotic factors have often been implicated by correlation, but ecological interactions, and the life history and morphological characteristics of the sponge species,
may also play key roles. Published studies vary widely in methods used, hampering direct
comparisons of results, and raising the possibility that conclusions might be influenced
by methods. I have been exploring the processes underlying distribution and abundance
patterns by applying identical methods to studying community composition and dynamics at two sites in Belize (Twin Cays) and one site in Panama (Bocas del Toro). Established
communities on roots have been fully censused, by volume and numbers of individuals,
yearly for three years (i.e., four censuses). Community composition, when evaluated in
terms of total volume of component species, is very similar at these three sites, although
abiotic factors differ and geographic distances between sites range from 330 m to 1,200
km. The nine species found on censused roots at all three sites constituted a total of 89%,
84%, and 73%, respectively, of the total sponge volume at these sites. In general, species
exhibited similar patterns of growth, size decrease, and mortality at all sites where they
were found, suggesting that these are species-level characteristics. Numbers of individuals and volume provide very different assessments of the relative importance of different
species in these communities. Community change over time appeared to be substantial,
when measured in terms of shifts in total numbers of individuals or total sponge volume.
However, taking into account dynamics of individual species provides a very different
view, as most large changes in numbers or volume were not community wide but tended
to reflect life history characteristics typical of early successional stage species or idiosyncratic responses of one or a few species to particular environmental circumstances.
