99. Multiple climate stressors produce complex trade-offs between metabolic costs and growth in subtidal tropical and temperate gastropods

Charlee A. Corra (1)*, Brian Helmuth (1), Sean D. Connell (3), and Bayden D. Russell (2)

1 Northeastern University, Boston, Massachusetts, 02155, USA
2 The Swire Institute of Marine Science and School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China
3 The University of Adelaide, Adelaide, South Australia

Background
The impacts to coastal marine ecosystems resulting from global climate change are increasingly obvious. Many gaps, however, remain in our knowledge of the role ocean acidification, in combination with warming, plays in organismal performance and survival. For example, how ocean acidification will interact with warming to alter the biological performance of benthic grazing species, and whether they will maintain their ecological function under these combined stressors, is poorly understood.

Methods
We exposed two tropical (Trochus sacellum and Turbo argyrostomus) and two temperate (Austrocochlea odontis and Turbo undulatus) species of subtidal gastropod to combinations of ambient and future temperature (ambient summer vs. +3°C) and CO2 (400 ppm vs. 1000 ppm) conditions. A variety of response parameters including Thermal Performance Curves (TPCs), ingestion rates, and growth rates were quantified after six weeks to elucidate the effects of different treatments on physiological performance and energetic partitioning.

Findings
After treatment exposure, responses to warmer temperatures and elevated CO2 varied significantly among treatments and species. Species demonstrated differential ability to acclimate and maintain metabolic function closer to that of individuals under contemporary temperature and CO2 levels. Importantly, the species that were able to alter metabolic function and satisfy higher metabolic demands under future conditions exhibited pronounced growth. This indicates that some species may acclimate to future conditions, however, in the absence of sufficient resources their high energetic demands may compromise their overall fitness.

Conclusions
Given these results, the divergence of metabolic and growth responses among species after exposure to increased temperature and CO2 indicate a diverse array of trade offs to these multiple climate stressors. Compromised fitness may result in reduced abundance of some grazer species under future conditions, which may lead to a breakdown in their ecological function and subsequent knock-on effects/impacts on local ecosystems due to decreased grazing pressure.