Patterns of rockpool molluscs in differing shore exposures

Abstract

Rockpools are understudied systems of extreme importance due to their proven vulnerability to climate change. Rockpool molluscs play essential ecological roles therein, directly by acting both as prey and predator and, indirectly by influencing the topography via grazing. However, the environmental factors driving their rockpool occupation remain largely unknown. Our study is one of the few to focus on rockpool molluscs community patterns, particularly at a large scale between shores of differing exposure to wave action, being the first focused assessment of rockpool molluscs in Portugal. Overall, 32 intertidal rock pools on four rocky shores were studied during the summer spring tide of 2015. We used multivariate analysis to evaluate the potential impact of sheltered versus exposed wave action, physical pool structure (length, width, and depth), and relationships within the pool community on the abundance and diversity of molluscs. Wave exposure significantly influenced mollusc abundance and diversity. Among the 37 different taxa identified, there was a greater abundance of grazing gastropods (62.2%), followed by bivalves (27.0%) and chitons (10.8%). We suggest that mollusc taxa may have preferences for particular rock pool habitats depending on the type of algae present rather than pool size. We also suggest that species-specific mollusc presence in rockpool can be related to their shell size, aperture, and foot size due to corresponding variation in musculature needed to hold the snail to the substrate in hydrodynamic conditions. Further investigation would benefit from disentangling the potential role of algal pool coverage as a predator refuge for molluscs.