Abstract

Aim: To describe the zoogeography of the algae-associated peracarid crustaceans from exposed rocky shores along the SE-Pacific. Location: Chile, 18°S to 42°S. Methods: A standardized sampling programme was used at all sites. Samples of macroalgae were taken at twenty sites distributed along the entire study area. Quantitative samples (n = 6 replicates of 8 cm-2 surface area each) of calcareous and non-calcareous red algae were taken in the low intertidal, preserved immediately in 4%-formalin and washed over a 0.2-mm mesh before sorting. All peracarid individuals were sorted, identified to the species level and then categorized in separate functional groups according to their feeding habits. Graphical representations of species replacement within each functional group along the latitudinal gradient are provided. A classification analysis employing the unweighted paired group method using arithmetic average (UPGMA) was conducted in order to reveal the main zoogeographical zones. Results: A total of forty epifaunal peracarid species was found. A gradual replacement of species within different functional groups (grazing and suspension-feeding species) was observed in the central region (c. 26°S-37°S). In this central region, species with northern and those with southern distribution overlapped, while other species were only found here, resulting in high species richness. The number of species/site/algal species in the northern (north of c. 25.5°S) and southern region (south of c. 38.5°S) was considerably lower than in the central region. The distribution of most grazing peracarids showed a more continuous pattern than that of suspension-feeding amphipods. The distribution of the remaining species (predators, scavengers, deposit-feeders, unknowns) was scattered along the examined sites. The cluster analysis for the epifaunal peracarid assemblage confirmed the separation of a northern and southern zone connected by a central (transitional) zone between c. 26°S and c. 37°S. Similar zonation patterns have been found by most other studies on the zoogeography of the Chilean coast, although little agreement exists about the exact limits of this transitional zone. It is discussed that the distribution limits of algae-associated peracarids (and other macroinvertebrates) - particularly in the transitional zone - may show interannual variations as a result of varying oceanographic conditions. The large affinity of the algae-associated peracarid fauna from the central and southern Chilean coast to those of other regions indicates that dispersal may be facilitated by rafting with floating algae transported in the Antarctic Circumpolar Current. Main conclusions: The zoogeographical analysis of algae-associated peracarids confirms the existence of a northern and a southern zone connected by an extensive transitional zone. General biology, habitat use and the abundant presence of dispersal vectors such as floating macroalgae may affect the zoogeography of species living in transitional zones with strong interannual variations in current regimes. In these areas, species associated with substrata of high dispersal potential may show different distribution patterns than species inhabiting other substrata.