A resilient fish is thriving in an inhospitable, jellyfish-infested region off Africa's south-west coast. And crucially it is helping to keep the local ecosystem going, and to preserve an important fishery.
The Benguela ecosystem lies off the coast of Namibia. It exists in waters only 120 metres deep that used to be a rich sardine fishery, but in the 1960s the sardine population crashed because of overfishing and environmental factors, and the region was invaded by algal blooms and swarms of jellyfish.
What's more, when the algae die they sink to the bottom and decay, releasing large quantities of the poisonous gas hydrogen sulphide. Nevertheless, local fish called bearded gobies have flourished in Benguela. Until now, nobody has understood how they survive it.
Anne Utne-Palm of the University of Bergen, Norway, and colleagues surveyed Benguela's gobies. Using acoustic tracking, they found that bearded gobies spend the daylight hours at the very bottom – the only backboned animals in the area to do so. Their stomach contents reveal that they feed off dead algae fallen from the surface, and also on the jellyfish.
The team found that the gobies could survive for hours in the oxygen-poor waters. They lower their metabolic rate to do so – but despite this they remain alert and can flee predators, as tank tests revealed.
At night the gobies head up to the surface to take in oxygen. They often hide themselves in the jellyfish clouds, where predators rarely venture.
Despite this, the gobies still fall victim to predators such as horse mackereland hake. This means that they act as a recycling system, ferrying nutrients that might otherwise be lost on the seabed back up to the surface.
"It's a lucky thing that the ecosystem had this goby," says Utne-Palm. "They bring lost resources back into the food chain."
Daniel Jones of the National Oceanography Centre in Southampton, UK, says that low-oxygen zones like Benguela are becoming more common as a result of human activities.
"It's good to see that some ecosystems can be sustained throughout this sort of hypoxic event," he says, "but I suspect that in a lot of environments there isn't a 'super-goby' around to help out."
The sardines may have gone, but horse mackerel and hake survive in the area by feeding on the gobies, and are regularly fished by humans. "If it weren't for the gobies, the human fishery would be in a worse condition than it is," says Jones.