Ocean warming and acidification; implications for the Arctic brittlestar Ophiocten sericeum

The Arctic Ocean currently has the highest global average pH. However, due to increasing atmospheric CO2 levels, it will become a region with one of the lowest global pH levels. In addition, Arctic waters will also increase in temperature as a result of global warming. These environmental changes can pose a significant threat for marine species, and in particular true Arctic species that are adapted to the historically cold and relatively stable abiotic conditions of the region. Consequently, we investigated some key physiological responses of brittlestar Ophiocten sericeum, a polar endemic which can dominate benthic infauna, to a temperature increase of 3.5A degrees C (ambient, 5-8.5A degrees C) and CO2 induced reduction in pH of 0.6 units (pH 7.7) and 1 unit (pH 7.3) below ambient (pH 8.3). Metabolism was upregulated at low pH. Faster arm regeneration stimulated by increased temperature was counteracted by low pH; at pH 7.3 in the high-temperature treatment, the maintenance of calcium carbonate structures in undersaturated conditions resulted in reduction in the rate of arm regeneration, possibly due to accelerated the use of energy reserves. If so, this could result in an energy deficit at times of increased energetic costs associated with responding to the combined factors of high temperature and low pH.