Protecting a Lagoon’s Food Chain, Top to Bottom

December 22, 2011

Researchers find that fishery closures in Belize’s Glover’s Reef help barracudas, groupers, and other predatory fish recover while the parrotfish and other herbivores essential for reef recovery still need more protection.

Sensitive coral reef ecosystems require a delicate balance of marine life to thrive. From the barracudas at the top of the food chain to the algae at the bottom, the system works together to keep itself healthy.

In an atoll reef lagoon in Glover’s Reef, Belize, WCS researchers have found that fishing closures produce encouraging increases in populations of predatory fish, like barracuda, groupers, and snappers. The numbers of herbivores like parrotfish and surgeonfish, however, grow only minimally with the closures. Because herbivorous fish feed on the algae that smother corals and inhibit reef recovery, they are essential to keeping the reef’s food chain in check.

The findings will help WCS researchers in their search for new solutions to the problem of restoring Caribbean reefs damaged by fishing and climate change.

The study’s authors include WCS conservationists Tim McClanahan, N.A. Muthiga, and R.A. Coleman, and their article appears in the journal Aquatic Conservation: Marine and Freshwater Ecosystems.

The team found that the modest recovery of herbivorous fish on Glover’s Reef has resulted in the overgrowth of algae, which has replaced the coral that covers the seafloor. While the coral once occupied 75 percent, it now represent less than 20 percent of the seafloor cover. The authors note that a recent national-level ban by the Belizean government on the fishing of parrotfish—a widespread herbivorous species—may be the key to reef recovery, provided that the fishing ban is enforced and met with compliance.

According to the authors, a number of factors could be contributing to the unpredicted responses of fishing closures. These include underestimates in the possible responses to bans on fishing, the limited size of the closed area, or the continued usage of the area by fishers in spite of the ban. The conservationists also mention that environmental factors such as oceanographic oscillations and warming waters complicate attempts to manage these ecosystems.

“It is encouraging to see the recovery of large predatory fish such as groupers and snappers under significant pressure elsewhere in Belize, but the lagging herbivorous fish is a warning that there is no single solution to coral reef conservation,” said Dr. Caleb McClennen, Director of WCS’s Marine Program. “While no-take zones are critical, more comprehensive ecosystem-based management is essential throughout the range of targeted species for long term recovery of the entire Meso-American Barrier Reef."

From Fiji to Kenya to Glover’s Reef, Dr. Tim McClanahan’s research examines the ecology, fisheries, climate change effects, and management of coral reefs at key sites throughout the world. This work has been supported by the John D. and Catherine T. MacArthur Foundation and The Tiffany & Co. Foundation. WCS wishes to acknowledge the Oak Foundation and The Summit Foundation for their generous support of this study and our marine conservation work throughout Belize.

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