Predatory fish bouncing back, but populations of critical algae-eating fish lag
By Summit Voice
SUMMIT COUNTY — Fishing closures in protected marine areas around the spectacular Mesoamerican reef near Belize have helped recover populations of barracuda, groupers, snappers, and other predatory fish, but herbivorous fish that clean algae from the coral are not faring as well.
Results of a long-term study by the Wildlife Conservation Society show that parrotfish an surgeonfish in the Glover’s Reef study area make only sight recoveries — not enough to reverse the degradation by caused by algae overgrowing the reefs and replacing the coral that once covered 75 percent, but now represent less than 20 percent, of the seafloor cover.
“The fishing ban in the fully protected portion of the lagoon was expected to result in an increase in predatory fish and — more importantly — herbivorous fish such as parrotfish that in turn reverse the degraded condition of algal dominance in this reef,” said Dr. Tim McClanahan, lead author of the study and head of WCS’s coral reef research and conservation program.
“What happened was a recovery of predatory fish, but not of the herbivorous fish, a finding that is forcing us to come up with a more effective model of reef management and recovery,” McClanahan said. “If the nation-wide ban on parrotfish is successful, then we can see if this type of large-scale management is the only effective solution for protecting coral reefs,” he addd.
The study appears in an online version of Aquatic Conservation: Marine and Freshwater Ecosystems. The authors include: Tim McClanahan, N.A. Muthiga, and R.A. Coleman of the Wildlife Conservation Society.
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. WCS provided valuable data through its monitoring program at Glover’s Reef to justify the landmark measure to protect reef grazers.
A number of factors could be contributing to the unpredicted responses of fishing closures. The complex web of species interactions may produce unexpected cascading effects because of underestimates in the possible responses to bans on fishing.
Additionally, the size of the closure may be too small to produce the desired effect, or there may not be enough compliance and enforcement. The study also mentions that environmental factors such as oceanographic oscillations and warming waters complicate any attempt to establish cause-and-effect relationships in these systems, as they noted a loss in coral cover across the 1998 El Niño that killed many corals worldwide.
“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.”