CO 2 -induced ocean acidification increases anxiety in Rockfish via alteration of GABA A receptor functioning

Abstract

The average surface pH of the ocean is dropping at a rapid rate due to the dissolution of anthropogenic CO 2 , raising concerns for marine life. Additionally, some coastal areas periodically experience upwelling of CO 2 -enriched water with reduced pH. Previous research has demonstrated ocean acidification (OA)-induced changes in behavioural and sensory systems including olfaction, which is due to altered function of neural gamma-aminobutyric acid type A (GABA A ) receptors. Here, we used a camera-based tracking software system to examine whether OA-dependent changes in GABA A receptors affect anxiety in juvenile Californian rockfish ( Sebastes diploproa ). Anxiety was estimated using behavioural tests that measure light/dark preference (scototaxis) and proximity to an object. After one week in OA conditions projected for the next century in the California shore (1125 ± 100 µatm, pH 7.75), anxiety was significantly increased relative to controls (483 ± 40 µatm CO 2 , pH 8.1). The GABA A -receptor agonist muscimol, but not the antagonist gabazine, caused a significant increase in anxiety consistent with altered Cl − flux in OA-exposed fish. OA-exposed fish remained more anxious even after 7 days back in control seawater; however, they resumed their normal behaviour by day 12. These results show that OA could severely alter rockfish behaviour; however, this effect is reversible.