How does rising atmospheric CO2 affect marine organisms?

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How Ocean Acidification and Warming Impact Predator-Prey Relationships of Calcifying Organisms
Landes, A. and Zimmer, M. 2012. Acidification and warming affect both a calcifying predator and prey, but not their interaction. Marine Ecology Progress Series 450: 1-10.

The authors write that "both ocean warming and acidification have been demonstrated to affect the growth, performance and reproductive success of calcifying invertebrates." However, they say that "relatively little is known regarding how such environmental change may affect interspecific interactions."

What was done
In a study designed to explore this real-world situation, Landes and Zimmer separately treated green crabs (Carcinus maenas, the predators) and periwinkles (Littorina littorea, their prey) under conditions that mimicked either ambient conditions (control) or warming and acidification (both separately and in combination), for a period of five months, after which the predators, their prey, and the predator-prey interaction were assessed for CO2- and warming-induced changes in response to the environmental perturbations they imposed on them.

What was learned
The two researchers report that "acidification negatively affected the closer-muscle length of the crusher chela and correspondingly the claw-strength increment in C. maenas," while "the effects of warming and/or acidification on L. littorea were less consistent but indicated weaker shells in response to acidification." And as might have been expected on the basis of these individual species responses to ocean acidification and warming (weaker claw strength in the predator, but weaker shells in the prey), Landes and Zimmer say that "on the community level," they "found no evidence that predator-prey interactions will change in the future."

What it means
The take-home message of the findings of Landes and Zimmer is well described in the closing sentence of the abstract of their research report: "Further experiments exploring the impacts of warming and acidification on key ecological interactions are needed instead of basing predictions of ecosystem change solely on species-specific responses to environmental change [italics and bold added]." Nature is complex; and our studies of it must be directed to gaining a better understanding of that species-interactive complexity, along with its implications for potential future global change.

Reviewed 29 August 2012