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The coastal waters off southwest Africa is going through troubling times, becoming effectively a dead zone with fish populations collapsing, jellyfish populations booming, and oxygen levels dropping. But one tiny fish, the bearded goby, seems to be perfectly adapted to these otherwise dead-end conditions, and is helping hold together and entire ecosystem by acting as an integral link in the food chain. As anchovies and sardine populations are wiped out by overfishing, the bearded goby has become the main source of food for practically everything else living in the ecosystem, but rather than collapsing along with other species, it seems to be flourishing -- much of that is thanks to its ability to survive with little oxygen and eat mud. Ars Technica reports on a study in Science, in which researchers used acoustic imaging of the ocean along with other analysis strategies to see how goby's were able to survive on the fringes of a dead zone -- a situation that normally spells disaster.
They found that the bearded goby is adapting perfectly to the new conditions. Unlike its competitors and predators, the bearded goby is able to happily coexist with jellyfish as well as survive in water low in oxygen, maintaining its reaction speeds to escape predators and avoiding heart or brain damage. To get extra oxygen when needed, the fish swim up to more oxygen-rich water at night while during the day, they stay safely buried in mud...which they also eat.
According to Discover Magazine, "For every tonne of fish currently swimming in the Benguela waters, there are more than three tonnes of jellyfish. Some scientists have suggested that the jellyfish explosion has trapped the region in a "trophic dead-end". Jellyfish have few predators so, having skyrocketed, their numbers are unlikely to fall back to levels where fish can return."
But that doesn't seem to be a problem for the goby. In addition to eating dead and sick jellyfish, the goby eat diatomaceous mud that is full of decomposed flora and fauna. With a diet made up of about 34% mud and about 60% jellyfish, the goby seem to be doing just dandy in the altered ecosystem. And that means they're a solid food source for other animals still surviving (though barely) in the poor habitat.
As Ars reports, "Species like the goby may be the difference between an ocean ecosystem that pulls through climate change and other human impacts, and an ecosystem that falls apart."
The goby "has the ability to consume what were considered dead-end resources and convert them into bite-sized chunks for higher trophic levels," Mark Gibbons, a University of the Western Cape biologist, told Discover Magazine. "Gobies have become anything but a dead-end resource. The gobies are now sustaining the rest of the ecosystem."
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