Assessing the Impact of Arsenic on Benthic Estuarine Fauna Behavior: Implications for Ecosystem Sustainability

Estuaries are dynamic ecosystems exposed to a wide range of stressors, including metal (loid) contamination. The assessment of the behavioral characteristics of the species inhabiting these ecosystems may provide a new point of view on chemical contamination since these behaviors generally regulate population dynamics and ecosystem stability. Therefore, this study aimed to investigate the changes in behavioral patterns of three estuarine benthonic species (the native polychaete Hediste diversicolor , the non-native polychaete Arenicola marina , and the native clam Scrobicularia plana ) when exposed to different concentrations of the metalloid arsenic (0, 0.5, 1.5, 4.5, 13.5, 40.5 mg/kg sediment). Behavioral assessment included bioturbation activity (measured by fluorescent particle remobilization) and determination of the maximum penetration depth by each species, both after 1 and 21 days of exposure. After 21 days of exposure, the ability of each species to burrow was evaluated. Results showed that the bioturbation activity of S. plana was immediately reduced by exposure to As (day 1) but disappeared with exposure time (day 21), whereas A. marina bioturbation activity was significantly increased from day 1 to day 21, expressing their highest values in sediments of 4.5, 13.5, and 40.5 mg of As/kg on day 21. For H. diversicolor , no changes were observed within each time or between the times. Results of the burrowing assay showed that A. marina nearly doubled its burrowing time, as well as increased in double its maximum penetration depth at As concentrations ≥1.5 mg/kg sediment. These results suggest that native species can be quite resilient to chemical contamination over time. However, the greater particle remobilization by the non-native species A. marina when exposed to As may cause displacement of the native fauna, disrupting the natural mutualism created in these environments, and possibly decreasing estuary functionality and biodiversity. Behavioral assessments under chemical exposure may improve the establishment of more feasible protection goals for more sustainable estuaries.