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15-Jul-2010

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Gobies gobble up the jellies



Benguela goby.
Image Hege Vestheim

Since the 1960s, the Benguela ecosystem off the coast of Namibia has experienced the collapse of the sardine fishery and a takeover by jellyfish and microbes. Surprisingly, a fish called the bearded goby has thrived in these conditions, partially fixing the food chain in this ecosystem, an international team of scientists explains in the in the 16 July issue of the journal Science.

This type of anoxic and jellyfish-dominated system is a growing problem around the world, due to overfishing. This is one reason why the Benguela system is particularly interesting.

The northern Benguela upwelling system on the southwest coast of Africa used to be one of the world's most productive ocean areas, supporting large fisheries. However, overfishing along with other environmental changes drove the collapse of the sardine fishery, dramatically changing the ecosystem.

To learn why the bearded goby was doing so well under these conditions, Anne Utne-Palm of the University of Bergen in Bergen, Norway and her colleagues sampled and analyzed the water and seafloor off the coast of Namibia in 2008. They combined these data with experiments on the behavior and physiology of the bearded goby, and they also looked at the gobies' stomach contents.

The results help explain why the gobies have been flourishing, even though they have become prey for seabirds and other animals that used to eat the sardines.

The researchers found that the gobies rest or hide in the sulfide- and algae-rich mud that has become common since these waters have lost much of their oxygen. They can do this because their bodies can withstand these low oxygen levels. The gobies also eat this mud as well as the jellyfish.

All of these adaptations help the goby thrive in conditions that are hard for other fish to tolerate. And, because larger fish and birds eat the gobies, these little fish are supporting a food chain that would probably otherwise break down, since not many other animals like to eat jellyfish.

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