Effect of swash climate and food availability on sandy beach macrofauna along the NW coast of the Iberian Peninsula

Abstract

The swash exclusion hypothesis (SEH) is widely used in explaining the abundance and diversity of macrofauna in sandy beaches. This hypothesis predicts a reduction in richness, abun- dance and biomass of macrofaunal assemblages from flat slope beaches to steep slope ones due to the swash climate. Nevertheless, flat slope beaches are characterised by greater food availability than steep slope beaches; thus, food supply may also explain macrofaunal trends in exposed sandy beaches. This paper investigates the relative importance of food availability (expressed as biopoly- meric carbon and chlorophyll a) and swash climate within this macrofauna impoverishment. Macro- faunal assemblages and sediment food availability were studied at 3 levels on the shore, 2 intertidal and 1 supratidal, at each of 11 sandy beaches located on the NW coast of the Iberian Peninsula. Results indicated that: (1) the beach slope had a stronger effect on richness, density and biomass of macrofaunal assemblages at the intertidal than at the supratidal level; (2) steep slope beaches pre- sented a higher percentage of active burrower species than flat slope beaches; and (3) species rich- ness, density and biomass of macrofauna were not related to food availability, measured as bio- polymeric carbon and chlorophyll a in the sediment. Overall, our results strongly support the idea that the harsh swash climate of steep slope beaches may exclude some species without active and rapid burrowing abilities, and is probably one of the mechanisms responsible for the observed decrease of macrofauna in this habitat.