The Earth’s biological systems will be exposed to continuing and accelerating increases in CO2 levels and temperature as we move further into the Anthropocene. Predicting the outcomes of these global changes requires an understanding of direct impacts, interactions, and feedbacks within natural ecosystems. I present results of in situ manipulations of CO2 and temperature in marine rocky intertidal systems which address responses at multiple levels of biological organization.
There were no significant changes in community diversity in response to these short term (< 1 month) manipulations. However, warming strongly impacted functioning over this time period, with the rate of productivity more than doubling under ambient CO2 levels relative to initial productivity values. Conversely, when CO2 was added, productivity was unaffected by warming. Productivity responses paralleled changes in the carbon-to-nitrogen ratio of a red alga, the most abundant primary producer species in the system. These observed changes in algal physiology and productivity in response to our manipulations indicate the potential for natural systems to shift rapidly in response to changing climatic conditions and for multiple environmental factors to act antagonistically. Furthermore, these results highlight the direct link between physiology and ecosystem function that bypasses community-level responses. Shifts in ecosystem productivity have the potential to elicit important biological feedbacks, including via changes in pH buffering capacity.