Program

Future temperature and CO₂ are predicted to change the structure and function of marine ecosystems by altering rates of both primary productivity and herbivory. Metabolic theories predict that increases in consumption should outstrip that of production, but this assumes that physiological rates will increase in consumers more than primary producers. I will draw together the results of several of our experiments assessing the effects of elevated temperature and CO₂ (ocean acidification) in subtidal marine systems, from physiological to ecosystem levels, in temperate and tropical systems. We show that under near-future scenarios herbivory provides ecosystem resistance by countering increased primary productivity in algal species which dominate under altered conditions. Interestingly, both metabolic rates and consumption of algae by gastropods reach thresholds, and decline, at cooler temperatures than primary productivity. In regions where the dominant grazers are molluscs, these results suggest that the ability of grazers to compensate for increasing primary production may be reduced under end of century conditions and, consequently, their ability to maintain ecosystem structure and function compromised.