Shell size variation and aggregation behavior of Littoraria flava (Gastropoda : Littorinidae) on a southeastern Brazilian shore

Littoraria flava is a common snail on rocky shores and stems of mangrove trees along the southeastern coast of Brazil. However, studies on this species are absent. Our previous observation indicated a distance distribution pattern among shell size classes of this snail, depending on distance from the shore and occurrence in aggregation. We hypothesized that (1) snails with large shells would occur on tree stems far from the shore and (2) snails occurring in aggregation on rocky shores would be smaller than those occurring in isolation. We evaluated the effect of desiccation on the mortality of different size classes of snails experimentally submitted to a temperature of 40 degrees C. We measured snail shells on 13 tree stems occurring in two mangrove strips (near and far from shore). Snails on tree stems of mangrove strips far from shore presented larger shells than snails near the short. Snails in aggregations on rocky shores were smaller than isolated ones. The desiccation experiment showed that small snails (< 1 cm) lost water at a faster rate than larger ones (> 1.55 cm) and the mortality of small snails was above 70%. The distribution pattern of L. flava is probably related to differential shell size class tolerance to prolonged periods of emersion. Also, aggregation may be a behavioral mechanism to avoid water loss, as small snails are frequently found in aggregation and lose water at a faster rate.