Effects of ocean acidification on the swimming ability, development and biochemical responses of sand smelt larvae

Ocean acidification, recognized as a major threat to marine ecosystems, has developed into one of the fastest growing fields of research in marine sciences. Several studies on fish larval stages point to abnormal behaviours, malformations and increased mortality rates as a result of exposure to increased levels of CO2. However, other studies fail to recognize any consequence, suggesting species-specific sensitivity to increased levels of CO2, highlighting the need of further research. In this study we investigated the effects of exposure to elevated pCO2 on behaviour, development, oxidative stress and energy metabolism of sand smelt larvae, Atherina presbyter. Larvae were caught at Arrábida Marine Park (Portugal) and exposed to different pCO2 levels (control: ~600μatm, pH=8.03; medium: ~1000μatm, pH=7.85; high: ~1800μatm, pH=7.64) up to 15days, after which critical swimming speed (Ucrit), morphometric traits and biochemical biomarkers were determined. Measured biomarkers were related with: 1) oxidative stress - superoxide dismutase and catalase enzyme activities, levels of lipid peroxidation and DNA damage, and levels of superoxide anion production; 2) energy metabolism - total carbohydrate levels, electron transport system activity, lactate dehydrogenase and isocitrate dehydrogenase enzyme activities. Swimming speed was not affected by treatment, but exposure to increasing levels of pCO2 leads to higher energetic costs and morphometric changes, with larger larvae in high pCO2 treatment and smaller larvae in medium pCO2 treatment. The efficient antioxidant response capacity and increase in energetic metabolism only registered at the medium pCO2 treatment may indicate that at higher pCO2 levels the capacity of larvae to restore their internal balance can be impaired. Our findings illustrate the need of using multiple approaches to explore the consequences of future pCO2 levels on organisms.

Early life history of larvae and early juvenile atlantic horse mackerel trachurus trachurus off the portuguese west coast

Early life history traits (ELHTs) are key to understand recruitment patterns in marine animals. However, for reef fishes, studies on ELHTs are mainly focused on tropical systems and little is known for temperate reefs. In this study we used SMURFs (Standard Monitoring Units for the Recruitment of Reef Fishes) to collect fish in a temperate rocky reef system (Arrábida Marine Park, Portugal) on a weekly basis for three months during the recruitment period. Six sub-surface SMURFs sampled 2490 Atlantic horse mackerel (Trachurus trachurus) postlarvae and juveniles. Sagittal and lapilli otoliths were extracted from a subsample of 296 fish and ELHTs, such as size and age at settlement, growth rate and age at first secondary growth formation were examined. Additionally, we tested three growth curves and selected the best suited to back-calculate the hatching pattern based on the lengths of all sampled fish. Standard length ranged from 6.13 mm to 48.56 mm and subsampled fish were aged between 19 days to 44 days. Age and size at settlement were estimated between 19 days and 36 days for individuals of 6.13 mm and 24.95 mm, respectively. Otolith shape changed clearly with increasing age and, on average, secondary growth started to form on day 33 (±3 days). Age/length relationship was well described by a Gompertz growth model which was used to back-calculate hatching dates. Four distinct hatching cohorts were identified with fish of the earliest cohort showing a faster body and otolith growth. This study indicates that the nearshore environment might have an important role in the early growth, development and hence recruitment of Atlantic horse mackerel. Information on the early life history of Atlantic horse mackerel is key to understand recruitment processes for this economically and biologically important species.