Future ecosystem resistance to a high-CO2 world: stabilising effect of ecological compensation

Chair: Ken Caldeira

Sean D. Connell (1)*, Giulia Ghedini (2), Bayden Russell (3)

1,2 The University of Adelaide, Adelaide, South Australia, 5005, Australia
3 The University of Hong Kong, Kong Hong

Background
The natural processes that stabilise ecosystems against change from enriched CO2 can be powerful, but there is almost no recognition for them among those that study climate change in the sea. In the absence of tests of compensatory processes to enriched CO2, we run the risk of over-estimating the effects of a high-CO2 world.

Methods
We tested the strength of compensatory processes that counter the effects of enriched CO2 to prevent community change. Experimental tests observed the countervailing strength of trophic compensation (i.e. herbivory) to absorb ecosystem change (i.e. the expansion of mat-forming algae to displace kelp forests).

Findings
CO2 drove a reversal in competitive dominance of habitat (from kelp to mats), but in the presence of herbivores this switch is countered by a proportional countervailing response that eliminates its otherwise unchecked effect. This capacity for adjustment in strength of trophic interactions, whilst acting as a relatively imperceptible mechanism to absorb global and local disturbances, enhances community stability well before significant loss of species occurs.

Conclusions
This capacity of natural systems to absorb the effects of CO2 without undergoing major change is a critical and almost unstudied aspect of future ecosystem stability. Compensatory effects are likely to maintain the resistance of communities to a high-CO2 world more deeply than current thinking allows.