Is there an indication of the origin of nutrient supply in different morphological structures of macrofauna at two different Brazilian southeastern sandy beaches? Comparison by C and N stable isotopes.

The goals of this study were to analyze if there is a difference in the stable isotopic ratio (δ13C and δ15N) of macrobenthic species sampled at two sandy beaches (one close to a river mouth and the other far from any freshwater input) and to identify differences in the stable isotopic ratio (δ13C and δ15N) in different body parts of three representative species of two Brazilian sandy beach macrofaunas: the polychaete Hemipodia californiensis, the mollusk bivalve Donax hanleyanus, and the crustacean decapod Emerita brasiliensis. No significant differences were detected in the δ13C stable isotopic ratio between the two sites analyzed; however, in the δ15N stable isotopic ratio, a significant difference was observed. Regarding the intraspecific response of stable isotopic ratio, D. hanleyanus showed a significant difference in carbon among different body part structures, while a trend for significance was observed for nitrogen isotopes. The differences were significant for both isotopes in E. brasiliensis, and no differences were observed among the body part structures in H. californiensis. There were significant differences in E. brasiliensis carapaces with regard to the δ15N stable isotopic ratio between the muscle and the whole body. Although the δ13C and δ15N stable isotopic ratio differs significantly in the digestive tract, muscles, and whole body of D. hanleyanus, such differences were not enough to determine changes in their trophic levels and food sources. Similar stable isotopic ratios were observed in the whole body, proboscis, and teeth of H. californiensis, highlighting this species as the top predator. In conclusion, stable isotopic analysis of benthic trophic structure can be employed as a tool in coastal management plans or environmental impact studies.

Evaluation of environmental quality of sandy beaches in southeastern Brazil.

The effect of urbanization on the environmental quality of two sandy beaches was evaluated using metrics such as pH, dissolved oxygen, coliforms and solid waste. Urbanization effects on physicochemical metrics (pH and dissolved oxygen) were not significant. The coliforms concentration was below the established limit for primary contact, but it was significantly higher on beaches with highest recreational potential. Similarly, the abundance of solid waste was significantly higher in urbanized areas (~4.5 items/m2), and it was higher than what was found for 106 beaches worldwide. Plastic represented 84% of the total number of items and recreational activities were the main sources of debris (80%). Therefore, a balance between recreation and conservation actions, based on short-term (e.g. fines) and long-term measures (e.g. educational policies) is recommended. We demonstrate that the use of multiple metrics provides more robust estimates of the environmental quality of sandy beaches than a single impact metric.

Extreme storm wave influence on sandy beach macrofauna with distinct human pressures.

We evaluated the influence of storm waves on the intertidal community structure of urbanized and non-urbanized areas of a sandy beach on the northern coast of Rio de Janeiro, Brazil. The macrofauna was sampled before (PREV) and after two storm wave events (POEV I; POEV II) in 2013 and 2014. Significant differences in community structure between PREV and POEV I in the urbanized sector demonstrate higher macrofauna vulnerability, and the community recovery within 41days on this scenario of less frequent events in 2013. On the other hand, significant differences in the macrofauna only in the urbanized sector between PREV and POEV II also highlight macrofauna vulnerability and community recovery failure within 42days on this scenario of more frequent storm in 2014. Urbanization and wave height were the variables that most influenced species, indicating that high storm wave events and increasing urbanization synergism are a threat to the macrofauna.