A paper published today in Global Change Biology finds that increased dissolved CO2 and decreased pH [so-called "acidification"] had the completely unexpected result of dramatically increasing reproduction [by 82%] in a coral reef fish. According to the authors, "This study provides the first evidence of the potential effects of ocean acidification on key reproductive attributes of marine fishes and, contrary to expectations, demonstrates an initially stimulatory (hormetic) effect in response to increased pCO2."
Increased CO2 stimulates reproduction in a coral reef fish
Gabrielle M. Miller et al
Ocean acidification is predicted to negatively impact the reproduction of many marine species, either by reducing fertilization success or diverting energy from reproductive effort. While recent studies have demonstrated how ocean acidification will affect larval and juvenile fishes, little is known about how increasing partial pressure of carbon dioxide (pCO2) and decreasing pH might affect reproduction in adult fishes. We investigated the effects of near-future levels of pCO2 on the reproductive performance of the cinnamon anemonefish, Amphiprion melanopus, from the Great Barrier Reef, Australia. Breeding pairs were held under three CO2 treatments (Current-day Control (430μatm), Moderate (584μatm) and High (1032μatm)) for a 9-month period that included the summer breeding season. Unexpectedly, increased CO2 dramatically stimulated breeding activity in this species of fish. Over twice as many pairs bred in the Moderate (67% of pairs) and High (55%) compared to the Control (27%) CO2 treatment. Pairs in the High CO2 group produced double the number of clutches per pair and 67% more eggs per clutch compared to the Moderate and Control groups. As a result, reproductive output in the High group was 82% higher than the Control group and 50% higher than the Moderate group. Despite the increase in reproductive activity, there was no difference in adult body condition between the three treatment groups. There was no significant difference in hatchling length between the treatment groups, but larvae from the High CO2 group had smaller yolks than Controls. This study provides the first evidence of the potential effects of ocean acidification on key reproductive attributes of marine fishes and, contrary to expectations, demonstrates an initially stimulatory (hormetic) effect in response to increased pCO2. However, any long-term consequences of increased reproductive effort on individuals or populations remains to be determined.