Hotter oceans may deplete commercial fish stock: study

With oceans warming over much larger spatial scale, marine ecosystems are under threat says a study

By Saiqua Sultan

Bangalore, January 18, 2018: Rising sea temperatures could harm commercial fish stocks by adversely affecting their source of food, a new study has found.

University of Adelaide scientists have demonstrated how increased temperatures reduce the vital flow of energy from the primary food producers at the bottom like algae, to intermediate herbivorous consumers to predators at the top of marine food webs.

Hadayet Ullah, a PHD student who conducted the study said the climate change led to expansion of cyanobacteria (small blue-green algae) which is unpalatable and not consumed by herbivores.

However, there are scientists who adopt another view to the claims made by the study.

Dr. D. Nagesh Kumar, Chairman, Centre for Earth Sciences says, “There is comfortable temperature zone for most of the fish to survive. They migrate to their comfort zone either in space or depth. Such comfortable temperature zones in sea are also called Potential Fishing Zones (PFZs). Thus the effects of rising sea temperature on fish stock would be for them to migrate rather than perish.”

Prof. Ivan Nagelkerken, the supervisor of the study told the Softcopy, “The oceans are generally warming over a much larger spatial scale than many fish migrate. Then there are many species that are territorial and don't migrate.”

“Also, different species migrate at different rates resulting in altered fish community compositions. And at the trailing edge (especially in the tropics) there are no fish to replace the original communities, leaving those areas denuded of healthy fish populations,” said Prof. Nagelkerken, who is also associate professor at the University of Adelaide.

Published in the open access journal PLOS Biology, the study was conducted with twelve large 1,600-litre tanks with a range of species including algae, shrimp, sponges, snails, and fishes where conditions of increased ocean temperature and acidity caused by increasing human greenhouse gas emissions were mimicked in the tanks.

The mini-food web was maintained under future climate conditions for six months, during which time the researchers measured the survival, growth, biomass, and productivity of all animals and plants, and used these measurements in a sophisticated food web model.