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Abstract. To evaluate the effects of beach morphodynamics upon the abundance, tidal movement, population structure and burrowing rate of the crab Emerita analoga (Stimpson) (Anomura, Hippidae) we sampled two beaches in south central Chile (ca. 42° S), Mar Brava and Ahui with dissipative and reflective characteristics, res­pectively. The swash zone at the dissipative beach was 5 – 6 times wider than that of the reflective beach. A at the dissipative beach, upwash speeds were higher and the number of effluent line crossings were lower by more than an order of magnitude. To examine the tidal movement of E. analoga, we collected crabs from 5 to 6 tidal levels of each beach every 2 h across 12 h of the tidal cycle. The intertidal distribution of crabs differed between beaches; i. e., at the dissipative beach they were primarily located at the swash zone, while at the reflective beach they were mostly located at the low tide level and shallow subtidal. The change in position of crabs was pronounced across the tidal cycle at the dissipative beach (Mar Brava), with most of the animals remaining in the active swash zone. Body size data were used to construct size frequency distributions for each population. Crabs from the dissipative beach reached larger sizes than those at the reflective beach. Sediments were coarser at the latter versus the former beach. Crabs burrowed at similar rates in the sand from both beaches, a result which supports the idea that E. analoga is a “sediment generalist” capable of burrowing successfully in a wide range of sediment types. This characteristic is likely a key to the broad success of this species on the full range of beach morphodynamic types along the coasts of South and North America.

Abstract. Eight sandy beaches were seasonally sampled along the coast of Chile, from ca. 21 to 42° S (about 3000 km) to study the relationship between community structure of the intertidal macroinfauna and beach characteristics. Sediment samples (0.1 m2, 30 cm deep) were collected (July – September 1998 and December 1998 – January 1999) with plastic cylinders at 15 equally spaced levels along three replicated transects extending from above the drift line to the swash zone. The sediment was sieved through a 1 mm mesh and the organisms collected stored in 5 % formalin. To define beach types, Dean’s parameter (Ω) was calculated from wave heights and periods, and fall velocity of sand particles from the swash zone. Crustaceans (mainly peracarids) were the most diverse group with 14 species, followed by polychaetes with 5 species. The talitrid amphipod Orchestoidea tuberculata, the cirolanid isopods Excirolana braziliensis and E. hirsuticauda and the anomuran decapod Emerita analoga were the most widely distributed and common species. Regression analyses between species richness, abundance and biomass of the whole macroinfauna versus sediment characteristics, beach face slopes and morphodynamic beach states showed no significant relationships. Thus, macroinfaunal community characteristics did not increase linearly from lower intermediate to higher intermediate or dissipative beach states as had been found before in Chile or in other coasts. A comparative analysis with data from sandy beaches of other world regions showed that the number of species inhabiting Chilean sandy beaches was generally lower, whereas total population abundances were generally higher compared with values reported elsewhere.

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