Modern coral reef fish may face greater competition for resources than 7,000 years ago
A school of blue-striped grunts (Haemulon sciurus) swim around the elkhorn coral (Acropora palmata) in the Caribbean. Modern coral reef food chains are shorter than they were about 7,000 years ago, a new study suggests.
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A school of blue-striped grunts (Haemulon sciurus) swim around the elkhorn coral (Acropora palmata) in the Caribbean. Modern coral reef food chains are shorter than they were about 7,000 years ago, a new study suggests.
Michael Aw/Oceanic Image Bank
Some ancient Caribbean fish 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 that about 7,000 years ago, researchers report February 11 Nature. Habitat loss and overfishing may have caused more species to compete for fewer resources and repositioned certain fish groups within the ecosystem’s food chain. The results suggest that fish may be less able to adapt if food sources suddenly become scarce, perhaps making current reefs even more vulnerable in an already changing environment.
“Understanding food webs helps us understand reef health,” says Jessica Lueders-Dumont, a fisheries ecologist and geochemist at Boston College in Chestnut Hill, Massachusetts. “If we could go back and scuba dive the same reefs a few thousand years ago, what would they look like?”
Rather than traveling back in time, Lueders-Dumont and his colleagues examined fossilized and modern fish ear stones. called otoliths which are important for movement and hearing. The shape of the otoliths depends on the species, and the team measured the amount of a heavy form of nitrogen to determine which creatures were lower or higher in the food chain. Animals higher in the food chain, such as sharks, have higher levels of heavy nitrogen than those of a lighter form. Prey have a lower ratio.
While modern fish appear to compete for similar food sources, many prehistoric reef fish had highly specialized diets, says Lueders-Dumont. “If you were a goby on a reef 7,000 years ago, you had your favorite little amphipod that you would eat, and that population of amphipods was on this little coral that you had access to.”
But today’s reefs have lost diversity, both at the top and bottom of the food chain. If a goby the coral has disappeared and there were fewer predators lurking around, the goby’s descendants could feed widely. But then more species could compete for the same resources, which could lead to problems.
It’s as if neighborhoods are replacing local restaurants that serve a variety of foods with national chains offering similar menus, Lueders-Dumont says. With fewer options available, “if the supply chain [for] beef or something is spoiled, then everyone is affected.
But there are signs of hope. In Panama, where authorities tightly control fishing, there are pockets of pristine coral reefs that appear to have healthier food webs than reefs in the Dominican Republic, where there is less monitoring. This shows that local management and conservation efforts can help give coral reefs a boost, says Lueders-Dumont. “Our behaviors and actions matter. We don’t need to bury our heads in the sand.”
