Effects of brine discharges on early benthic stages of Concholepas concholepas.

Desalination plants are becoming increasingly important in Chile due to drought-related challenges affecting both drinking water supplies and the mining industry. However, the potential effects of brine discharges on local marine species remain poorly understood. In this study, small juveniles of Concholepas concholepas (Chilean abalone), the most economically important marine resource exploited along the Chilean coast, were used to assess the effects of brine discharges from a rural reverse osmosis desalination plant. Laboratory experiments involved exposing individuals to brine solutions with salinities ranging from 58 to 34 PSU for 6 h, followed by a 12-hour recovery period in control seawater (34 PSU). No mortality was observed during or after exposure across all salinity levels. However, sublethal traits were negatively affected. Foot adhesion was completely absent at 58 PSU, reduced to ca. 80 % at 52 PSU compared to control, and unaffected at lower salinities. After recovery, adhesion performance returned to control levels at 52 PSU but remained impaired at 58 PSU. Self-righting success was zero at 58 PSU and only partially recovered after 12 h in control water. Self-righting time was significantly prolonged by ca. 100 % at both 52 PSU and 45 PSU, but returned to baseline values only at 45 PSU and remained elevated at 52 PSU. Oxygen consumption measured after the recovery period was not significantly different across treatments, suggesting recovery of metabolic homeostasis. These findings indicate that although acute mortality is not a concern, hypersaline conditions from undiluted brine can significantly impair essential behavioural traits in C. concholepas juveniles. These sublethal effects are likely confined to areas near brine discharge points and diminish with dilution. Our results underscore the importance of incorporating behavioural and sublethal endpoints into environmental assessments of desalination activities in coastal ecosystems.