Effects of Ocean Acidification on Dopamine-Mediated Behavioral Responses of a Coral Reef Damselfish.

We investigated whether CO2-induced ocean acidification (OA) affects dopamine receptor-dependent behavior in bicolor damselfish (Stegastes partitus). Damselfish were kept in aquaria receiving flow through control (pH -8.03; pCO2 -384 mu atm) or OA (pH -7.64; CO2 -1100 mu atm) seawater at a rate of 1 L min-1. Despite this relatively fast flow rate, fish respiration further acidified the seawater in both control (pH-7.88; pCO2 -595 mu atm) and OA (pH-7.55; pCO2 -1450 mu atm) fish-holding aquaria. After five days of exposure, damselfish locomotion, boldness, anxiety, and aggression were assessed using a battery of behavioral tests using automated video analysis. Two days later, these tests were repeated following application of the dopamine D1 receptor agonist SKF 38393. OA-exposure induced ceiling anxiety levels that were significantly higher than in control damselfish, and SKF 38393 increased anx-iety in control damselfish to a level not significantly different than that of OA-exposed damselfish. Additionally, SKF 38393 decreased locomotion and increased boldness in control damselfish but had no effect in OA-exposed damselfish, suggesting an alteration in activity of dopaminergic pathways that regulate behavior under OA conditions. These re-sults indicate that changes in dopamine D1 receptor function affects fish behavior during exposure to OA. However, subsequent measurements of seawater sampled using syringes during the daytime (-3-4 pm local time) from cre-vasses in coral reef colonies, which are used as shelter by damselfish, revealed an average pH of 7.73 +/- 0.03 and pCO2 of 925.8 +/- 62.2 mu atm; levels which are comparable to Representative Concentration Pathway (RCP) 8.5 pre-dicted end-of-century mean OA levels in the open ocean. Further studies considering the immediate environmental conditions experienced by fish as well as individual variability and effect size are required to understand potential im-plications of the observed OA-induced behavioral effects on damselfish fitness in the wild.