Sand smelt ability to cope and recover from CO2-induced ocean acidification stress during early stages assessed through development and biochemical responses

Abstract

Marine biodiversity is being threatened by the increased uptake of atmospheric CO2, known as ocean acidification. Although the majority of literature points to negative and abnormal effects to future acidification scenarios in short term exposures, most fail to evaluate and recognize the potential adaptation capacity and its effects among populations and species. Here, the effects and the capacity of the sand smelt larvae Atherina presbyter to respond to different pCO2 levels (control: ~600 μatm, pH = 8.03; medium: ~1000 μatm, pH = 7.85; high: ~1800 μatm, pH = 7.64) were measured, addressing larval development characteristics, oxidative stress, and energy metabolism. Recently, Silva et al. (2016) demonstrated that the exposure of these larvae to increasing levels of pCO2, leads to higher energetic costs and morphometric changes, and points to a decrease in the antioxidant response capacity. However, in that study, larvae were exposed to only a short 15-days period. In the present study we aim at: 1) investigating the potential of sand smelt larvae to acclimate to acidification conditions by exposing larvae to increasing CO2 levels for 45 days; 2) determine the ability of sand smelt larvae to recover from stressful conditions induced by exposure to high CO2 levels. Individuals were collected at the coastal area of the Arrábida Marine Park (Portugal), transported to the laboratory and randomly assigned and exposed to three different pCO2 levels. After 30 days of exposure, larvae were either switched between treatments or left in the original treatment for another 15 days. Larvae were randomly sampled at 0, 15, 30, and 45 days, photographed for morphometric analysis, weighed, and stored at -80ºC until biochemical analysis were performed. The biochemical biomarkers measured were related with: 1) oxidative stress and damage: superoxide dismutase and catalase enzyme activities, as well as lipid peroxidation and DNA damage levels; and 2) energy metabolism: total carbohydrate, protein and lipid levels as measures of available energy; electron transfer system activity as a measure of oxygen and energy consumption; cellular energy allocation; and lactate dehydrogenase and isocitrate dehydrogenase enzyme activities. Results suggest particular sensitivity of sand smelt to increasing levels of pCO2 seen by the alteration in their global energetic status and by the oxidative stress effects. The results contribute simultaneously to an integrative view of the ocean acidification effects and adaptation capacity of this species during environmental stress.