Sandy beach macroinfauna from the coast of Ancud, Isla de Chiloe, southernChile

Six sandy beaches were sampled on the coast of Ancud, Isla de Chiloe, south ern Chile (ca. 42 degrees S) with the following purposes: 1) to study commu nity structure and across shore zonation of the intertidal macroinfauna in relation to different beach types, and 2) to analyze how similar or differe nt is the taxonomic composition and community structure of the macroinfauna l assemblages, compared to those inhabiting sandy beaches located further n orth of Canal de Chacao, the limit between Isla de Chiloe and the mainland coast. Sediment samples (0.1 m(2), 30 cm deep) were collected (April-May 19 98) with plastic cylinders at fifteen equally spaced levels along three rep licated transects (separated by 1 m) extending from above the drift line to the swash zone. The sediment was sieved through a I mm mesh and the organi sms collected stored in 5% formalin until sorting. To define beach types, t he Dean's parameter was calculated from wave heights and periods, and sand fall velocity of sand particles from the swash zone. The calculations show that one of the sites was a dissipative beach, while the other five had ref lective or low intermediate beach characteristics. The highest number of sp ecies and total macroinfaunal abundance occurred at the dissipative site ( 1 1 species and 59705 ind m(-1), respectively), the lowest at the most refl ective site (3 species and 507 ind m(-1), respectively). In general, the ab undance of organisms found were higher than those predicted by a worldwide model of sandy beach community structure. The talitrid amphipod Orchestoide a tuberculata, the cirolanid isopod Excirolana hirsuticauda and the anomura n decapod Emerita analoga, were the most abundant species at all beaches bu t one. Kite diagrams and cluster analyses show that in general, three fauni stical belts occur across the intertidal of the beaches studied. The across shore distribution of the macroinfauna was more related to a sand moisture gradient than to grain size or sediment compactness. Taxonomic composition , community structure and across shore zonation of that macroinfauna were s imilar to that from beaches located further north of Canal de Chacao.