Interactive effects of ocean acidification and warming on subtidal mussels and sea stars from Atlantic Canada

Abstract

Anthropogenic CO₂ is decreasing oceanic pH and contributing to seawater warming. We tested the effects of low pH and high temperature at levels predicted for 2100 on an ecologically important predator–prey system (sea stars, Asterias rubens, and mussels, Mytilus edulis) from the NW Atlantic coast. Mussels are dominant competitors for space and important ecosystem engineers, while sea stars control mussel populations and thus local community structure. We found sea stars to be negatively affected in growth rate by low pH, with growth further reduced by a high temperature. In contrast, mussel growth rate was positively affected by low pH, with no response to temperature within the tested range. Predation of sea stars on mussels, measured as per-capita consumption rate, decreased in acidified conditions by 50%. Our study suggests that mussels may not be negatively affected by pH at the levels predicted for the end of this century and that mussels may be subjected to a reduced predation from sea stars under future conditions.

Key words:

• Asterias
• mussel
• Mytilus
• Nova Scotia
• ocean acidification
• ocean warming
• sea star

Acknowledgements

We thank Christopher Harley and Jocelyn Nelson for introducing us to acidification experiments and two anonymous reviewers for useful comments on the original manuscript.

Supplementary material

Supplementary material for this article is available via the Supplemental tab of the article's online page at http://dx.doi.org/10.1080/17451000.2014.932914

Editorial responsibility: Geir Ottersen

Additional information

Funding

Funding: This project was funded by grants awarded to R.A.S. by the Canada Research Chairs program (CRC), the Canada Foundation for Innovation (CFI), and the Natural Sciences and Engineering Research Council (NSERC, Discovery Grant) and by a grant awarded to S.C.C. by the Department of Fisheries and Oceans Canada (DFO).