Seasonal dynamics of amphipod assemblages in intertidal coralline algal mats on two Brazilian shores

Coralline algae form important rocky intertidal habitats, but their function may be radically changing worldwide as increased land deforestation may ultimately lead to higher sedimentation rates over algal mats, and more frequent extreme weather conditions may increase physical disturbances. One way of addressing how environmental change may affect the ecosystem function of coralline algal mats is to examine the temporal dynamics of invertebrate assemblages associated with this habitat, and how they correlate to key environmental factors. Here, we investigated the dynamics of amphipod assemblages inhabiting coralline algal mats at two sites in southeastern Brazil from September 2010 to August 2013. Twenty-two different species were recorded, encompassing two life-styles (free-living and tube-dwelling), and four feeding habits (detritivorous, omnivorous, herbivorous, and carnivorous). Consistently across sites and over the years, species diversity peaked in autumn, together with the passing of cold fronts and increased wave height. Physical disturbance through wave action caused algal mat thinning and reduced overall amphipod abundance, suggesting habitat limitation, but also decreased species dominance, allowing other species to build up populations over autumn and winter. The omnivore generalist Apohyale media (Dana, 1853) tended to dominate in spring and summer, when the environment was more stable, and the organic matter retained in sediments was higher. When environmental conditions changed during autumn and winter, a second omnivore, Hyale niger (Haswell, 1879), took over, especially in years 1 and 3. During year 2, the virtual absence of H. niger allowed the detritivore Lysianassa temimino Senna and Souza-Filho, 2010 to thrive, which was likely facilitated by the retention of assorted sediments.