Littorine foraging behavior and population structure on a wave-exposed shore: Non-linear responses across a physical gradient

Littorines often use topographical features (e.g., holes, crevices) for she lter. We investigated this behavior (% outside of natural crevices and arti ficial holes during daytime low tides) over a cross-shore wave force gradie nt. Whereas maximal wave force (MWF) declined linearly with increasing dist ance from the low tide mark, percent outside increased along this gradient and reached an asymptotic level (70%) 40 m from the low tide mark. A compar ison of seasonal averages of percent outside and MWF showed an abrupt trans ition between high and low values of percent outside with increasing MWF, b ut comparisons of daily data were more varied, presumably due to the superi mposition of other environmental factors (e.g., desiccation), Contrary to e arlier descriptive studies and biomechanical predictions, larger littorines were found in locations closer to the low tide mark where MWF were higher, suggesting that size-limitation from hydrodynamic forces does not occur wi thin the size range studied (1-8 mm) when shelters are available. However, the restriction of littorines to areas near shelters can greatly influence community structure by permitting the development of algal assemblages in e xposed locations.