Thermal limits of estuarine amphipods and their implications for aquaculture production

Estuarine systems are characterised by strong seasonal fluctuations in temperature and salinity, exposing species to physiological challenges that can limit their survival. Amphipods are naturally abundant in estuaries and have gained attention in aquaculture for their high nutritional value and suitability to large scale production. Their commercially feasible production will only be achieved if these are cultured in open or semi-open earthen pond systems, where temperature and salinity naturally fluctuate. As such, the physiological resilience of amphipods to such fluctuating environmental conditions is key for their production. The present study investigated the thermal limits of the amphipod species Melita palmata, Marinogammarus marinus, and Gammarus locusta under habitat-specific salinity regimes to assess their resilience to environmental variability relevant to aquaculture production using earthen ponds. Thermal limits, assessed via critical thermal maximum (CTmax), revealed species-specific patterns: M. palmata and M. marinus exhibited similarly high CTmax values (>33.5 °C), indicating a stronger thermal tolerance; G. locusta showed a lower CTmax (31-32 °C), but the highest thermal safety margin. Based on its biological traits and biochemical profile, G. locusta was selected for an experiment testing the influence of salinity on its thermal limits. Specimens reared under a salinity gradient (15-35) displayed significantly higher CTmax at higher salinities, regardless of sex. Amphipods maintained at the lowest salinity tested (15) displayed a lower mass-to-length ratio and lower CTmax values, indicating energetic costs associated with osmotic stress. Understanding how thermal and osmotic gradients modulate amphipod physiology is paramount to develop climate-resilient production strategies.