Habitat harshness and morphodynamics: life history traits of the mole crab Emerita brasiliensis in Uruguayan sandy beaches

Abstract

The habitat harshness hypothesis (HHH) pos- tulates that in reflective beaches the harsh environment forces organisms to divert more energy towards main- tenance and they therefore have lower abundance, fecundity, growth and survival rates than in dissipative beaches. Recent investigations have tested this hypoth- esis through single comparisons of only two beaches, and thus the observed trends in population level vari- ables cannot be attributed incontestably to the beach state, but only to location. Here, abundance, reproduc- tion, recruitment, population structure and body size of the intertidal mole crab Emerita brasiliensis were com- pared between populations from eight microtidal ex- posed sandy beaches with contrasting morphodynamics, sampled bimonthly during 22 months throughout the 180 km Uruguayan Atlantic coast. Physical variables and compound indices of the beach state were used to categorize sandy beaches. The results of this bi-annual large-scale analysis were fully consistent with the pre- dictions of the HHH: abundance (total and population components), duration of the reproduction and recruit- ment seasons and the individual size of megalops and females of the mole crab E. brasiliensis decreased from dissipative to reflective beaches. This was reflected by linear or, mostly, nonlinear relationships between bio- logical and both physical variables and compound indices of beach state. In conclusion, this multi-beach sampling provides compelling evidence of a consistent response of demographic and life history traits of an intertidal beach species to morphodynamic characteristics.