Saving Coral Reefs Is Harder Than We Think

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Most researchers look at single species in isolation, ignoring the complex relations within coral communities. That needs to change.

By Nathan Collins


(Photo: Wikimedia Commons)

The world’s coral reefs are, in no uncertain terms, under attack by climate change. As oceans warm, they absorb carbon dioxide and become more acidic, killing off coral in the process. Unfortunately, relatively little is known about how ocean acidification effects coral reef ecosystems as a whole—and now’s the time to do something about it, researchers argue in a new paper.

Though coral reefs are probably best known for being really pretty, they also provide food for millions, are among the most diverse ecosystems in the world, and are a vital economic resource, providing jobs in the fishing, recreation, and tourism industries. But global warming is threatening coral reefs, which in turn threatens us. When temperatures increase, coral often “bleaches,” meaning they release the algae that gives them their color—and which they need to survive. Warming and increasing acidity in oceans rips apart the basic links that keep reef communities together. Just last week, Australian scientists announced the worst bleaching yet in the Great Barrier Reef, the world’s largest coral reef system.

Yet whether we know enough to save reef ecosystems—or even predict what’s going to happen to them—is unclear.

“There are concerns about the future of coral reefs in the face of ocean acidification and warming, and although studies of these phenomena have advanced quickly, efforts have focused on pieces of the puzzle rather than integrating them to evaluate ecosystem-level effects,” researchers led by Peter Edmunds write today in BioScience.

In particular, most studies focus on how ocean acidification might impact single coral species, and the research is often conducted in laboratory tanks rather than out in the ocean (where coral naturally live). While scientists have learned much from those studies, they don’t yet have an idea of how things play out when taking account of the complex web of interactions between species in a reef ecosystem.

The key challenge, the authors write, is understanding how the effects of ocean acidification—in particular, the increase in calcium carbonate concentrations as the planet warms—change with scale. We know different coral and algae species respond differently to increased ocean acidity, but it’s also known that biological systems like reefs are not simply the sum of their parts. Warming could help certain algae species, for example, complicating our understanding of the otherwise obvious consequences of bleaching.

To begin to address those issues, Edmunds and hiscolleagues propose breaking down coral ecosystems at five scales: coral and algae cells; whole organisms; populations of individual species; local reef communities, including many different species; and the reef ecosystem as a whole. Factors like temperature and nutrient flow will affect reef systems at all levels, of course, but it’s most important that we begin to understand how effects on one scale play out on another. For example, understanding acidification’s effects on populations of corals and algae requires (among other things) a deeper understanding of how an individual organism’s survival and reproduction are effected. On the other hand, understanding individuals’ responses depends on a deeper knowledge of how resources are shared among a population and throughout the ecosystem.

Fortunately, many of the theoretical tools for understanding ecosystems at multiple scales already exist in ecology—they just haven’t been applied to reefs yet, the authors write. Once they are applied, “they offer great potential for integrating the effects of ocean acidification across scales on coral reefs.”