Prey Fish Turns Predator
Aug-03-2010

A mystery is brewing off the south west coast of Africa.

A particular species of small fish, typically no larger than the length of your hand, is thriving in the oxygen-depleted, jellyfish-ridden waters, and scientists have no idea how.

An international team of researchers studied the bearded goby (Sufflogobius bibarbatus), a harmless creature that normally feeds on phytoplankton and provides a rich food source for predators like penguins, seals and larger fish.

They discovered that the community of gobies was behaving in strange and interesting ways.

They're eating the same jellyfish who normally prey on them.

"We don't know if they are eating dead jellyfish from the bottom, or if they are coming up to oxygen-filled layers to eat jellyfish, but they are eating jellyfish," Victoria Braithwaite, a Penn State University professor of fisheries and biology and team researcher, said in press release.

Jellyfish started to overpopulate the waters that stretch from Namibia to South Africa in the 1960s and 1970s. That was right around the time that sardine populations plummeted in the region due to overfishing, allowing jellyfish numbers to explode since there was less competition for food.

Now the gobies' adaptations are bringing jellyfish -- usually a "dead end" food source because almost nothing preys on them -- back into the circle of life.

The scientists also discovered that the gobies were capable of living on the ocean floor for at least 10 to 12 hours at a time, a place Braithwaite described as a "toxic sludge" where hardly anything lives except bacteria and nematodes.

"Somehow the gobies can withstand the toxic environment, but we don't know exactly how they are doing it," she said.

"When we touch them with a rod, they show rapid escape responses," she said, meaning that the gobies remain very alert despite the low-oxygen environment.

"It is a win-win situation where the gobies are using a resource that is usually a dead end in the ocean: the jellyfish," said Braithwaite.

"And they are using the toxic mud as a refuge," she added. "Together this seems to explain why their population is growing despite the fact that they are now being the main prey species in this unusual ecosystem."

Posted by Clay Kohut at 12:00 AM - Link to this entry  |  Share this entry  |  Print