Effect of ocean acidification on early life stages of Atlantic herring (Clupea harengus L.)

Abstract. Due to atmospheric accumulation of anthropogenic CO₂ the partial pressure of carbon dioxide (pCO₂) in surface seawater increases and the pH decreases. This process known as ocean acidification might have severe effects on marine organisms and ecosystems. The present study addresses the effect of ocean acidification on early developmental stages, the most sensitive stages in life history, of the Atlantic herring (Clupea harengus L.). Eggs of the Atlantic herring were fertilized and incubated in artificially acidified seawater (pCO₂ 1260, 1859, 2626, 2903, 4635 μatm) and a control treatment (pCO₂ 480 μatm) until the main hatch of herring larvae occurred. The development of the embryos was monitored daily and newly hatched larvae were sampled to analyze their morphometrics, and their condition by measuring the RNA/DNA ratios. Elevated pCO₂ neither affected the embryogenesis nor the hatch rate. Furthermore the results showed no linear relationship between pCO₂ and total length, dry weight, yolk sac area and otolith area of the newly hatched larvae. For pCO₂ and RNA/DNA ratio, however, a significant negative linear relationship was found. The RNA concentration at hatching was reduced at higher pCO₂ levels, which could lead to a decreased protein biosynthesis. The results indicate that an increased pCO₂ can affect the metabolism of herring embryos negatively. Accordingly, further somatic growth of the larvae could be reduced. This can have consequences for the larval fish, since smaller and slow growing individuals have a lower survival potential due to lower feeding success and increased predation mortality. The regulatory mechanisms necessary to compensate for effects of hypercapnia could therefore lead to lower larval survival. Since the recruitment of fish seems to be determined during the early life stages, future research on the factors influencing these stages are of great importance in fisheries science.