Mosaic Of Environmental Conditions Research Articles

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

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.

Repeatable patterns of small-scale spatial variation in intertidal mussel beds and their implications for responses to climate change

The interaction of ocean conditions and weather with small-scale physical features of a habitat can have profound effects on the experiences of individual organisms. On topographically complex shorelines, and particularly within dense aggregations of organisms such as mussel beds, a mosaic of environmental conditions can develop, and the resulting variation in conditions within the aggregation could drastically alter the performance of neighboring individuals. Using a suite of sensors mounted to individual Mytilus californianus mussels over two summer field deployments, we have characterized the temperature variation and valve gaping behavior differences found at two spatial scales: within a group separated by centimeters, and between groups of mussels located at the upper and lower extents of the natural mussel zone separated by meters. While temperature conditions near the lower edge of the mussel bed were generally more benign, temperature extremes were similar at both heights in the bed, and variation in body temperature among neighbors increased as the daily mean temperature increased. These patterns were similar across years despite a 3.8 °C difference in mean air and seawater temperatures between years. Gaping behavior was also highly variable among individuals, though that variability diminished at the high end of the mussel bed where the total time mussels spent submerged was much more constrained. These data indicate that an individual mussel's physiological status and past history can be drastically different than those of its nearby neighbors, complicating our ability to characterize representative conditions within a habitat. These observations also provide for the possibility that the impacts of future climate change will be highly specific to certain individuals based on their relative exposure or protection within the mosaic. To address such possibilities, future work must examine the correlation between genotypic and physiological traits that determine performance and individuals' unique experiences in their disparate micro-environments.