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Under the sea, breadcrumb trails are leading scientists to a new understanding of how ecotourism can affect marine ecosystems.
Tourism operators around the world commonly bait snorkeling and diving sites with morsels of bread to entice fish—improving tourists’ experiences and the operators’ bottom lines. According to a new study conducted in the Cook Islands, however, the tactic is actually changing fish behavior.
At two coral reefs popular among snorkelers, researchers studied which fishes were swimming about before, during, and after they crumbled a loaf of bread over the water. After the feeding, they found that there were more fish overall, but from fewer species. Only a quarter of the fishes—mostly carnivorous and omnivorous species—actually ate the bread.
Sowing the reef, however, hurt smaller herbivorous fishes. The surge in activity caused “all this turmoil in their environment,” says Natalie Prinz, a doctoral candidate at the University of Waikato in New Zealand and the study’s lead author.
The bread prompted a feeding frenzy that temporarily created what ecologists call a “landscape of fear.” Since the fishes that were interested in the food tended to be predatory, it scared away smaller herbivorous fishes that didn’t want to become targets once the bread was gone. The bread-induced landscape of fear also disrupted the natural foraging of specialized feeders, such as sturgeon, a species key to maintaining reef health, which is deterred in crowded environments.
The researchers think baiting could also be having other long-term effects on the reef. Giving fish food from outside their natural diet could change the composition and distribution of their excrement, which may negatively affect the growth of coral on the seafloor.
On coral reefs, “everything relies on everything else,” says Danielle Dixson, a marine scientist at the University of Delaware who was not involved in the research. “Tiny changes can have huge implications.”
Previously, research has shown that feeding large marine mammals alters their behavior, health, population size, and migration patterns. Measures to prohibit artificial feeding have been enacted around the world, but they often overlook smaller animals like birds and fish.
The researchers also looked into what tourists thought of tour operators’ feeding practices. Everyone on the tours said they would have still enjoyed their experience without artificial feeding, suggesting that restricting the activity may not hurt the tourism industry. Of course, Prinz says, it’s hard to know if the tourists would have felt the same if they hadn’t just had a successful, fish-filled tour.
There are many well-studied alternatives to increase fish numbers that don’t rely on artificial baiting, Dixson says, such as reducing local fishing, improving shoreline vegetation, creating marine protected areas, and restricting polluting sunscreens. Prinz says that even feeding the fish less often, or with more natural foods, such as fish scraps or fish food pellets, could mitigate some of the unintended consequences.
Ultimately, such small steps could make a big difference, Prinz says. “I think global tourism could slowly but surely become so much more sustainable.”