Spatio-temporal variability of the surf-zone fauna of two Ecuadorian sandy beaches

Abstract

Temperate and subtropical sandy beach surf zones present diverse and abundant fauna that are important in local food webs. However, dynamics of these fauna have been poorly studied in tropical areas. The aims of the present study were to describe the small swimming surf-zone fauna (~1–5mm in length) of two Ecuadorian sandy beaches, determine whether this fauna varies with beach, season or tide, and explore the environmental factors correlated with faunal variability. Beaches were sampled in wet and dry seasons during high, mid- and low tide (2001–2002) by using a hyperbenthic sledge. Beaches were inhabited by an abundant and diverse fauna (>1200 individuals per 100m2 and >30 taxa), where most individuals were in their early life stages (65%), and the dominant taxa included mysid shrimp (>40% of individuals) and fish and crab larvae (>25 taxa). Composition of groups that are present during their entire life or only early life stages varied most strongly between beaches, potentially because of differences in wave exposure and the influence of an adjacent river, and between seasons with changes in coastal oceanic currents. These results suggest that despite the environmental stability often portrayed for tropical environments, Ecuadorian surf-zone fauna are spatially and temporally variable.