Losing ecosystem resistance to change: when grazers fail to compensate for primary productivity

Chair: Ivan Nagelkerken

Bayden D. Russell (1)*, Charlee A. Corra (2), Giulia Ghedini (3), Nicole L. Mertens (3) and Sean D. Connell (3)

1 The Swire Institute of Marine Science and School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China.
2 Northeastern University, Boston, Massachusetts, 02155, USA
3 Southern Seas Ecology Laboratories, School of Biological Sciences, The University of Adelaide, Adelaide, SA, Australia.

Background
Future temperature and CO2 are predicted to change the structure and function of marine ecosystems by altering rates of both primary productivity and consumption. 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.

Methods
I draw together the results of several of our experiments assessing the effects of elevated temperature and CO2 (ocean acidification) in key subtidal marine grazers, from physiological to ecosystem levels (aquarium to mesocosm to CO2 vent).

Findings
We show that under near-future scenarios herbivory provides ecosystem resistance by countering increased primary productivity in algal species which dominate under altered conditions. However, both metabolic rates and consumption of algae by gastropods reach thresholds, and decline, at cooler temperatures than primary productivity. Therefore, under end-of-century conditions primary productivity is likely to outstrip consumption in some subtidal systems.

Conclusions
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 will be compromised