Temperate coastal fish shows resilience to extreme low pH in early larval stages

Abstract

Fishes have shown varying responses to the decline in seawater pH associated with ocean acidification. Coastal marine species inhabit characteristically dynamic environments which requires physiological adaptation to variability, including fluctuations in pH and associated carbonate chemistry parameters. Our study assessed the response of the early life stages (postflexion) of a common coastal fish species (Diplodus capensis) that is found in coastal nearshore and estuarine habitats along the South African coastline. We assessed their metabolic and behavioural response to a range of pH conditions which covered a high pH (8.02), the lowest pH that they are naturally exposed to (7.75) as well as extremely low pH levels (∼7.75–7.27) exceeding their current range of exposure, which may occur with future coastal acidification. Our findings suggest that this species is metabolically tolerant of acute low pH conditions (down to 7.27 pH) showing no changes in either routine or active metabolic rates. Although our study identified a slight increase in swimming activity in D. capensis larvae exposed to low pH, there was no change in feeding activity. These results suggest that this species may have the physiological capacity to withstand the present and future high pH variability associated with its environments, in the absence of other stressors and ecological interactions. However, the increased swimming activity at low pH may translate into downstream ecological impacts, for which the mechanisms need to be assessed with further research.