By Chris PalmerCoral reefs have the capacity to bounce back from climate-related devastation, provided human beings do not hinder their recovery. This was the glimmer of hope offered up by Scripps Institution of Oceanography Assistant Professor Stuart Sandin to a near-capacity audience at Monday’s Jeffrey B. Graham “Perspectives on Ocean Science” lecture hosted by the Birch Aquarium.
Sandin’s lecture, “Coral Reefs: Ecosystems in Decline,” the latest in the Perspectives’ series, in its tenth year, chronicled the marine ecologist’s travels around the world to assess the health of the notoriously fragile coral reef ecosystems.
Sandin conducted the majority of his research in the remote Line Islands archipelago, located near the equator in the Central Pacific Ocean. Two of the Line Islands are inhabited while another two are not, making the archipelago a unique setting in which to study the impact of human activity on reef ecosystems.
“We can study how the ecosystem structure changes with the presence of people, primarily their fishing activity,” said Sandin.
Not surprisingly, Sandin found that the coral reef surrounding the uninhabited islands was more robust. The reef also contained significantly more fish, and importantly, a much higher ratio of predators to prey. This is critical because predator fish maintain the numbers of smaller herbivorous prey fish at stable levels. Herbivorous fish nibble away at the roots of seaweed, which is the glue that holds coral reef together. When humans fish they tend to remove the large predator fish, resulting in a proliferation of herbivorous fish and setting of a chain reaction that culminates in a devastating degradation of coral reef.
According to Sandin, climate change is compounding the impact of overfishing via a ratchet effect. “As you have one warm water event, corals die. They may start to regrow, but before they regrow enough, they get hit by another event and another, and what you see is less and less coral.”
Sandin pointed to a promising case study illustrating the natural resilience of coral reef ecosystems. In 2002 the Phoenix Islands became the largest protected marine area in the Pacific, with all fishing activity banned. Shortly afterwards, these islands were hit by a year-long El Niño event that raised water temperatures by a few degrees, resulting in losses of up to 90-percent of coral reef in some areas.
Nearly a decade later, the devastated coral has almost grown back pre-2002 levels. “If given a chance, these corals do have a chance to bounce back.”
“There is a balancing act between protection and use,” Sandin said of our need to fish in a way that is sustainable and that allows coral reefs to maintain their natural resilience.
To underscore this message, Sandin ended the lecture with a quote by the noted conservationist Aldo Leopold. “Health is the capacity of the land for self renewal. Conservation is our effort to understand and preserve this capacity.”
Monday’s lecture will be available to watch online in two weeks on the UCSD-TV website, which currently hosts 10 years worth of previous ‘Perspectives’ lectures.
The next lecture will be on Dec. 12 and will feature biological oceanographer Lisa A. Levin discussing deep-ocean ecosystems and the environmental and economic threats they face.