SIZING IT UP: DEVELOPMENT OF A SPECIMEN-BASED DATABASE OF BODY-SIZE FOR WESTERN ATLANTIC MOLLUSKS

Interpretation of temporal and geographic patterns in fossil body size variation is difficult without understanding modern trends and mechanisms. Despite the considerable attention that has focused on investigation of large-scale spatial variations in the body size of Recent molluscs, (with particular interest in variations of body size across biogeographic boundaries and along latitudinal gradients), there is still much debate regarding the generality of observed trends and the underlying processes that drive them (e.g., food availability, competition or life-history traits). In particular, the mechanisms that control modern body size distributions at the scale of local communities and regional faunas still require testing.

We present a new and growing database of body size for selected gastropods and bivalves of the Western Atlantic focusing particularly on taxa that exhibit a circum-Caribbean distribution. The database currently includes data for 390 species (c. 16000 specimens; 5400 specimen lots) that represent a range of trophic life-styles taken from adult specimens reposted in malacological collections. This database will allow a wide range of questions about modern body size distribution to be addressed as well as acting as a baseline for comparison with fossil data.

Size variations along geographic clines are demonstrated by statistical and graphical approaches. Analyses to date among species sharing distributions around the Florida Peninsula and Caribbean suggest little difference in the geographic distribution of body-size maxima. At a finer geographic scale, however, it is apparent that particular areas within both regions have a tendency towards larger sized specimens. Western Florida has more maximum size records than elsewhere in the region while the Lesser Antilles archipelago provide the most size maxima from the Caribbean. It remains to be seen whether these patterns hold up following increased sampling and the incorporation of additional taxa.