A unique fish species has adapted to a hostile environment, poisonous to most other marine organisms, becoming an important part of a food chain that includes other fish, birds and mammals in the coast of Namibia.
The small fish, about 13 cm long, called the Benguela-goby, or bearded goby (Sufflogobius bibarbatus), is found only on the anoxic continental shelf off Namibia and South-Africa.
After over-fishing of the sardines in the late 60s and early 70s, drastic changes occurred in the coastal environment which caused an excess of microalgae that accumulated on the bottom and over time produced a thick layer of rotting mud. This produced a shift in the food web of the Benguela ecosystem and jellyfish increased in abundance. The gobies also increased in number by occupying areas of the damaged environment and feeding on the nutritious mud and the newly abundant jellyfish. Penguins, seals, sea birds and larger commercial fish, that had previously fed almost exclusively on sardines, switched to eating mostly gobies.
African penguins (Spheniscus demersus) are threatened birds that live off the coast of Namibia and South Africa. They used to feed mostly on sardines, now they can also feed on gobies.
Scientists from Norway, South Africa and Namibia became interested in finding how this little fish manages to live and prosper in an environment that is lethal to other fish.
Anne Christine Utne-Palm from the University of Bergen and her collaborators discovered that during the day the goby stays on the oxygen deprived seabed. Here it seems to “hold its breath”, while it feeds on the mud and associated small organisms. Later, during the night, the goby swims up to the surface waters where it recovers its oxygen deficit and digests its food.
IMR - Gov. Norway
Three gobies on sulphide-sediment at 130 m depth.
When the gobies swim up to shallower waters at night, they associate with jellyfish. This is a night-time shelter from predators because goby predators avoid jellyfish. The gobies, however, are largely indifferent to jellyfish staying close and even swimming in between their stinging tentacles. The fish also feeds on the smaller jellyfish. According to the researchers:
“Physiological adaptations and anti-predator and foraging behaviors underpin the success of these fish. Gobies consume jellyfish and sulphidic diatomaceous mud, transferring "dead-end" resources back into the food chain.”
The research findings, published today in the journal Science, modify former understanding of the structure and functioning of marine food-webs. Previously the belief was that fish could not survive in an environment of sulphide-rich, low oxygen mud or in the midst of stinging jellyfish. But the bearded goby has shown to be tolerant to these extreme environments.