Long-term exposure to salinity variations induces protein carbonylation in the copepod Acartia tonsa

Salinity is a key variable influencing the life history of aquatic organisms. Environmental variability in salinity has been associated with increases in the formation of reactive species, ending up in a state of oxidative stress. In copepods, information about effects of salinity variations mostly includes data from short-term experiments where the effects of salinity changes are evaluated in terms of survival and vital rates, and data involving oxidative stress biomarkers are limited. Here, we experimentally evaluate the effects of long-term salinity variations in the estuarine copepod Acartia tonsa through the analysis of protein carbonylation, vital rates (egg production, EPR; ingestion, IR) and gross growth efficiency (GGE). Cultured copepods were subjected to alternate salinity increases and decreases between S = 10 and 20, in steps of 5 units every 12 h, during 15 days (Sv treatment). A control group (no salinity change) was subjected to the same manipulation but in a constant salinity condition (S = 15). Protein carbonylation was higher in females under the Sv treatment compared to control, whereas in males this was not observed. However, males presented significantly higher levels of protein carbonylation than females, irrespective of experimental condition. EPR was higher in control while IR was higher in Sv treatment, but differences were not significant. Instead, GGE showed clear cut and significant differences between Sv and control. While decreased GGE was indicative of significantly increased metabolic expenditures under variable salinity condition, higher oxidative damage was likely a side effect of increased metabolic demands and production of reactive oxygen species.