Environmental correlates of distribution across spatial scales in the intertidal gastropods Littoraria and Echinolittorina of the Indian coastline

Abstract

ABSTRACT Marine habitats are a mosaic of environmental conditions, which can limit species distributions despite the high dispersal potential offered by ocean currents. Periwinkle snails from the genera Littoraria and Echinolittorina disperse using planktotrophic larvae and have wide ranges in the Indo-Pacific, but patchy local distributions along the Indian coastline. To understand the environmental drivers of distribution in these intertidal snails, we used species distribution models executed in Maxent at both coastline and ocean basin scales. We obtained location information from primary and secondary sources, and used environmental predictors related to species survival, growth and reproduction spanning terrestrial and marine realms. Explanatory environmental variables broadly corresponded between scales, with maximum sea surface salinity and tidal range being common factors across species differing in their dispersal potential and habitat specificity. The Indian coastline exhibits a steep salinity and tidal range gradient, which may influence adult or larval survival through desiccation stress. In contrast to global-scale studies, temperature and productivity rarely emerged as important at the Indian coastline scale, indicating that variation along other environmental axes can drive distribution patterns at smaller spatial scales and within tropical coastlines. The results from our study provide specific hypotheses related to species-environment relationships that can be tested using field experiments to understand the drivers of species range along the Indian coastline.