Fluctuating asymmetry of two crustacean species on fourteen sandy beaches of Rio de Janeiro State

Sandy beaches are the most frequented coastal environments in the world, and they consequently suffer different types of impacts due to the rapid urban occupation and demographic growth in coastal regions, which generate stressful conditions for the resident species and reduce the environmental quality of the beaches for resident species. Crustaceans can be used as reliable bioindicators of human stress, and the amphipod Atlantorchestoidea brasiliensis and the decapod Emerita brasiliensis are highlighted. One tool for evaluating the environmental quality and the instability of individual development is fluctuating asymmetry (FA), which measures small, random deviations from a perfect bilateral symmetry. To evaluate the environmental quality of the beaches, some indices have been developed in recent years; among the most used are the conservation, recreation and urbanization indices, which offer easy-to-use metric for decision makers. This study aimed to quantify and compare the levels of FA in the populations of A. brasiliensis and E. brasiliensis on 14 beaches in Rio de Janeiro State with different levels of urbanization and conservation. For each species, two individual indices and two composite indices of asymmetry were calculated and tested in four bilateral traits. The urbanization, recreation and conservation indices were used to assess environmental quality of the sandy beaches. The results of the present study indicate a complex spatial distribution of FA in relation to the indices of the environmental quality of the beaches. The beaches that obtained the highest values in the conservation index obtained the lowest values of FA for both species. The beaches located in the Metropolitan region, specifically in the city of Rio de Janeiro, generally presented the highest levels of FA for both species. These species are susceptible to different forms of impacts due to their distinct characteristics in feeding behavior, development mode and beach zone occurrence. A. brasiliensis is more susceptible to direct impacts on the beach, such as recreational activities, while E. brasiliensis is more sensitive to impacts on water (contamination and physicochemical changes). Our results indicate that fluctuating asymmetry can be used as a good tool to evaluate impacts on sandy beaches, but additional studies should be conducted to improve the understanding of the spatial distribution of FA on sandy beaches.