Biogeographical patterns of benthic macroinvertebrates in the SoutheasternPacific littoral

Aim To use new collections and taxonomic reviews of the Chilean coastal bio ta, and studies on biodiversity oil a reappraisal of Southeastern Pacific l ittoral biogeography. Location The temperate coastline of the Southeastern Pacific, extending ove r 6000 km from northern Peru to the southern tip of Chile. Methods Records of coastal macroinvertebrates were assigned to ten geograph ic zones along the Chilean coast. The Spearman rank correlation coefficient , rho, was used to establish the relationship between the total number of s pecies and the number of single records for each zone. Regions and underlyi ng faunal gradient were verified via unweighed paired group method using ar ithmetic averages (UPGMA), and ordination non-metric multidimensional scali ng (nMDS) analysis based on a disagreement distance matrix of presence/abse nce data. Abundance down-weighting was preferred to rare species down-weigh ting, owing to the nature of the records, where a larger number of referenc es for a given taxon did not necessarily a greater abundance or commonness. The dissimilarity matrices between the different zones were used to establ ish the degree of agreement between the different levels of analysis, using a weighted Spearman rank correlation coefficient p(w). Statistical signifi cance was established using a randomization (permutation) test. Main conclusions Analysis of new macroinvertebrate data and taxonomic revie ws of the Chilean coastal fauna indicates a Transitional-Temperate Region f or the Southeastern Pacific littoral, located between 35 degrees S and 48 d egrees S where a gradual mixing and replacement of species negates previous hypotheses on the existence of a marked distributional break at 42 degrees S.