Macrofaunal assemblages associated with coralline turf: Species turnover and changes in structure at different spatial scales

Abstract

Our aim was to analyse changes in species turnover and structure of macrofaunal assemblages associated with intertidal coralline algal turfs at 4 spatial scales along the coast of Argentina (southwestern Atlantic): provinces (∼106 m), localities (∼104 m), sites (∼10 2 m) and replicate quadrats (∼1 to 3 m). Corallina officinalis was by far the dominant algal species in most samples, but C. elongata and Jania rubens var. rubens were also frequent. Frond density was 3 times higher in the southern, cold-temperate Chubut province than in the northern, warm-temperate Buenos Aires province. Macrofaunal species richness, diversity and evenness were also significantly higher in samples from Chubut than in those from Buenos Aires, with 'province' explaining 86 to 98% of the variance in the analytical model. In total, 118 macrofaunal taxa belonging to 11 invertebrate phyla were found. Mytilid bivalves and polychaetes were the most important groups contributing to differences between provinces. Brachidontes roddguezii was extremely abundant in Buenos Aires province, while Rhynchospio glutaea and Perumytilus purpuratus were dominant in samples from Chubut. Changes in assemblage structure were significant at the scale of provinces, localities and sites in Patagonian localities. Measures of beta diversity showed that taxonomic turnover was correlated with distance between samples at scales of 10 4 m or higher, with the highest at the scale of provinces. Higher biodiversity in the Magellan assemblage than in warmer areas of the northern coast of Argentina may be related to the Pacific origin of the Magellan fauna, which entered the southwestern Atlantic during the Tertiary period.