Some ancient fish in the Caribbean may have lost their lunch.
Modern food chains on coral reefs off the coasts of the Dominican Republic and Panama are roughly 60 to 70 percent shorter than they were around 7,000 years ago, researchers report February 11 in Nature. Habitat loss and overfishing may have pushed more species to compete for fewer resources and repositioned some fish groups within the ecosystem’s food chain. The findings suggest fish could be less able to adapt if food sources suddenly become scarce, perhaps making today’s reefs even more vulnerable in an already changing environment.
“Understanding the food webs helps us understand the health of the reef,” says Jessica Lueders-Dumont, a fisheries ecologist and geochemist at Boston College in Chestnut Hill, Mass. “If we could go back, scuba dive on the same reefs a couple thousand years ago, what would they look like?”
Rather than time travel, Lueders-Dumont and colleagues examined fossilized and modern fish ear stones called otoliths that are important for movement and hearing. Otolith shape depends on species, and the team measured the amount of a heavy form of nitrogen to determine which critters were lower or higher in the food chain. Animals higher in the food chain, like sharks, have higher ratios of heavy nitrogen over a lighter form. Prey have a lower ratio.
While modern fish seem to be competing for similar food sources, many prehistoric reef fish had highly specialized diets, Lueders-Dumont says. “If you were a goby on a reef 7,000 years ago, you had your favorite little amphipod that you would eat, and that amphipod population was on this one little coral that you had access to.”
But today’s reefs have lost diversity at both the top and the bottom of the food chain. If a goby’s coral went extinct and there were fewer predators lurking around, the goby’s descendants might forage widely for food. But more species may then compete for the same resources, which could spell trouble.
It’s as if neighborhoods replaced locally owned restaurants that serve a variety of foods with national chains that offer similar menus, Lueders-Dumont says. With fewer options available, “if the supply chain [for] beef or something gets messed up, then everybody is affected.”
But there are signs of hope. In Panama, where officials tightly control fishing, there are pockets of pristine coral reefs that seem to have healthier food webs than reefs in the Dominican Republic, where there’s been less oversight. That shows local management and conservation efforts can help give coral reefs a boost, Lueders-Dumont says. “Our behaviors and our actions matter. We don’t need to bury our heads in the sand.”
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