How will food webs respond to the multiple effects of ocean acidification and warming in marine ecosystems?

Much of the ocean acidification research to date has focused on the responses of single species to increasing CO₂ and warming. While we know that ocean acidification and warming can have negative effects on calcifying organisms, potentially affecting already compromised coral-reef ecosystems, we know much less about the potentially counteracting effects of elevated CO₂ on primary producers and their consumers. Is it possible that organisms, placed within the context of their food webs, gain some resilience from the effects of climate change? The study of a Swedish estuary showed that the response of this ecosystem to ocean acidification and warming is modulated by complex food web interactions. The implications of this study may be wide-ranging if changes in food webs decrease the ability of ecosystems to respond to climate change. Will the loss of top consumers make ecosystems less resilient to climate change? This is a question that needs to be considered as both food webs and global climate change.

Future directions

While the Swedish estuary experiment shows that a consumer can affect an ecosystem’s response to climate change, climate change can also affect a consumer’s role in an ecosystem. A good example is the recent dramatic shift in polar bear and orca whale observations in the Canadian Arctic. Sea ice in the Arctic is melting at unprecedented rates as the result of global warming. Polar bears need this sea ice to stalk their prey, mainly seals, but have been driven to inland hunting grounds with the loss of ice. Orca whales, by contrast, are unable to hunt their preferred prey, other species of whales, in ice-covered waters. As ice continues to melt, orcas have been spotted in areas of the Arctic where they have never been seen before. Some people have suggested that this shift from seal predation to whale predation could have important ecosystem-level effects as the food webs shift in response to the decline of sea ice.