Ecological Resilience

You’ve probably heard the word resilience, perhaps used to describe someone’s ability to recover from an illness or bounce back after an injury. It turns out that resilience also has a scientific meaning that is similar to the one you’re familiar with. Ecological resilience refers to an ecosystem’s ability to cope with or absorb change.

The natural environment is constantly changing—from day to night, El Niño to La Niña, etc. Forty years ago, the term resilience was first used to describe the persistence of communities in the face of environmental change (Holling 1973). Resilience took off as a concept in marine ecology around the time that many Caribbean reefs shifted from a coral-dominated system to one in which macroalgae (seaweed) had the upper hand. This alternate stable state is thought to have resulted from a combination of factors that slowly degraded the ecosystem over time until disease wiped out sea urchins, which were the last abundant herbivore. Without urchins, macroalgae gained the upper hand and took over from corals. Because of the degraded state of the reefs, there was no “backup” system to compensate for the loss of urchins—in other words, the reefs had lost their resilience.

Recently, the idea of resilience has gained renewed interest in the face of global climate change. As the threats to reefs escalate—think increasing temperatures and ocean acidification—ecologists, conservation professionals, and resource managers are trying to understand what they can do to increase their system’s ability to cope with change. This requires improving our scientific understanding of what allows some reefs to fare reasonably well even in the face of environmental disturbance. There have been some recent discoveries that are shedding light on this. For example, scientists studying the reefs of Ofu Island in American Samoa have found that heat resistant corals turn on genes that allow them to cope with heat stress before they experience hot water. This “front loading” may give them an edge up in coping with thermal stress. Read the study here.

However, our scientific understanding of resilience lags behind our need to take action now to reverse declines in reef health. Importantly, we lack the scientific tools to measure coral reef resilience when many stressors affect the reef at the same time. Without this understanding, the scientific community is unable to give managers and conservation practitioners empirically-driven advice about the relative merits of alternative management interventions. In other words, until scientists can describe what it will take for reefs to remain resilient, their advice will not be any better than “herbivorous fish are good for reefs, and nutrient pollution is bad for reefs.” Yet real world management questions are more nuanced and often involve tradeoffs: how many herbivores are needed, how much nutrient pollution can reefs take, should management focus on overfishing or coastal development, can local conservation offset or limit the effects of climate change? Our research in Palmyra is a step toward answering those questions.