Ocean acidification has no effect on thermal bleaching in the coral Seriatopora caliendrum

The objective of this study was to test whether elevated pCO2 predicted for the year 2100 (85.1 Pa) affects bleaching in the coral Seriatopora caliendrum (Ehrenberg 1834) either independently or interactively with high temperature (30.5 °C). Response variables detected the sequence of events associated with the onset of bleaching: reduction in the photosynthetic performance of symbionts as measured by maximum photochemical efficiency (F v/F m) and effective photochemical efficiency (delta F/F m') of PSII, declines in net photosynthesis (P net) and photosynthetic efficiency (alpha), and finally, reduced chlorophyll a and symbiont concentrations. S. caliendrum was collected from Nanwan Bay, Taiwan, and subjected to combinations of temperature (27.7 vs. 30.5 °C) and pCO2 (45.1 vs. 85.1 Pa) for 14 days. High temperature reduced values of all dependent variables (i.e., bleaching occurred), but high pCO2 did not affect Symbiodinium photophysiology or productivity, and did not cause bleaching. These results suggest that short-term exposure to 81.5 Pa pCO2, alone and in combination with elevated temperature, does not cause or affect coral bleaching.

CO2-induced ocean acidification increases anxiety in Rockfish via alteration of GABAA receptor functioning

The average surface pH of the ocean is dropping at a rapid rate due to the dissolution of anthropogenic CO2, raising concerns for marine life. Additionally, some coastal areas periodically experience upwelling of CO2-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 (GABAA) receptors. Here, we used a camera-based tracking software system to examine whether OA-dependent changes in GABAA 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 CO2, pH 8.1). The GABAA-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.