RNA-seq reveals a diminished acclimation response to the combined effects of ocean acidification and elevated seawater temperature in Pagothenia borchgrevinki

Purpose: The IPCC has reasserted the strong influence of anthropogenic CO2 contributions on global climate change and highlighted the polar-regions as highly vulnerable. With these predictions the cold adapted fauna endemic to the Southern Ocean, which is dominated by fishes of the sub-order Notothenioidei, will face considerable challenges in the near future. Recent physiological studies have demonstrated that the synergistic stressors of elevated temperature and ocean acidification have a considerable, although variable, impact on notothenioid fishes. The present study explored the transcriptomic response of Pagothenia borchgrevinki to increased temperatures and pCO(2) after 7, 28 and 56 days of acclimation. We compared this response to short term studies assessing heat stress alone and foretell the potential impacts of these stressors on P. borchgrevinki's ability to survive a changing Southern Ocean. Results: P. borchgrevinki did demonstrate a coordinated stress response to the dual-stressor condition, and even indicated that some level of inducible heat shock response may be conserved in this notothenioid species. However, the stress response of P. borchgrevinki was considerably less robust than that observed previously in the closely related notothenioid, Trematomus bernacchii, and varied considerably when compared across different acclimation time-points. Furthermore, the molecular response of these fish under multiple stressors displayed distinct differences compared to their response to short term heat stress alone. Conclusions: When exposed to increased sea surface temperatures, combined with ocean acidification, P. borchgrevinki demonstrated a coordinated stress response that has already peaked by 7 days of acclimation and quickly diminished over time. However, this response is less dramatic than other closely related notothenioids under identical conditions, supporting previous research suggesting that this notothenioid species is less sensitive to environmental variation. (C) 2016 Elsevier B.V. All rights reserved.