Intertidal microhabitats as a shelter for assemblages of chitons at southern Chile

Environmental heterogeneity is one of the main hypotheses promoting changes in species diversity. Several abiotic and biotic factors that promote environmental heterogeneity generate physical and biological microhabitats, where organisms may find refuge from environmental stress. The abundance, species richness and body size structure of chiton assemblages were estimated in different intertidal microhabitats. These microhabitats (physical: crevices, pools, and boulders; biological: mussel beds, arborescent algae, and crustose algae) were sampled in six sites of the southern Chilean coast during the austral spring of 2016. The results of our study exhibited the species Chiton granosus as the most abundant, followed by C. magnificus and Tonicia chilensis. Species richness and abundance were higher in physical microhabitats, with boulders and crevices showing the highest values, respectively. The multivariate analyses revealed three groups with high similarities within them; the first group represented by crevices, pools, and mussel beds; the second group composed of arborescent and crustose algae; and the third group comprised by boulders. Mussel beds were considered “nursery grounds” for harbouring a high abundance of juveniles of C. granosus (<10 mm), whilst physical microhabitats and algae host the biggest specimens of both C. magnificus and T. chilensis (>30 mm). We suggest that in biological microhabitats, the patterns of species richness and abundance and body size structure would be determined by a relation of functional specificity derived from feeding habits; and, in physical microhabitats, these patterns would be explained by a relation of behavioural specificity derived from negative phototactism.