Nature 577, 370–375 (2020)

Increasing CO2 levels in the ocean will lower the pH, creating a more acidic environment. Research has shown that fish sensory systems and behaviour are affected under these conditions, with reef fish particularly sensitive to pH decreases. However, differences between studies and species responses require further investigation to draw conclusive predictions of impacts.

Timothy Clark of Deakin University, Geelong, Australia and co-authors conducted three years of experiments to replicate previous studies and advance the field of fish behavioural response to ocean acidification. The study used over 900 individual coral reef fish from six species across different life stages and looked at avoidance of predator chemical cues, fish activity levels and preference of turning direction. Experiments were carefully documented to ensure transparency.

The authors found no consistent change in the studied behaviours under predicted end-of-century ocean acidification. They suggest that this difference could be a result of small sample sizes and methodological or analytical weaknesses in previous studies, and warn against results showing small within-group variance.