Geographic variation in sandy beach macrofauna community and functional traits

Abstract Sandy beaches are a common ocean-dominated ecosystem along the north coast of Spain. We conducted field surveys at 39 beaches distributed between 1° and 9°W, ca. 2000 km along this geographic region to document broad patterns of macrobenthic communities, and to describe their association with variables characterising both the beach environment and the characteristics of the adjacent ocean waters. Macrofaunal functional traits are considered to be an informative measure that can be useful for many ecosystem-level questions, as they are based on what organisms do (i.e., their ecological function) rather than on their identification alone. Boosted regression-trees analysis showed that the occurrence of the main taxonomic groups and feeding guilds were differentially associated with the prevailing beach features along this coastline. The occurrence (presence/absence) of molluscs was best explained by the concentration of chlorophyll- a and wave exposure whereas those of crustaceans and polychaetes were best explained by an ensemble of variables including beach slope, sea surface temperature and grain size. A comparison of the feeding guilds demonstrated that the occurrence of suspension feeders was best explained by chlorophyll- a and wave exposure, whereas the occurrence of deposit feeders was best explained by beach slope, sea surface temperature and chlorophyll- a . The occurrence of predators and scavengers was best explained by sea surface temperature and beach slope. Based on the patterns presented here, we confirm that the upwelling events that occur regularly on this coastline are a structuring agent for beach communities. Future work needs to examine the role of the oceanographic conditions of the region for they might represent the driving forces behind large-scale shifts in macrofauna communities.