Energy-transfer disturbances caused by ocean warming can cut the amount of food available to top predators, they say – which in turn can harm the many marine species within the food-webs.

In the just-published study, twelve 1600-litre tanks were constructed to mimic predicted conditions of elevated ocean temperature and acidity caused by increasing human greenhouse-gas emissions. The tanks held a range of species including algae, shrimps, sponges, snails and fish.

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

Lead author PhD student Hadayet Ullah and supervisors Prof Ivan Nagelkerken and Associate Prof Damien Fordham showed that increased temperatures reduced the vital flow of energy from the primary food producers at the bottom (such as algae), to intermediate consumers (herbivores), to predators at the top of marine food-webs.

“While climate change increased the productivity of plants, this was mainly due to an expansion of cyanobacteria (small blue-green algae),” said Ullah.

“This increased primary productivity does not support food-webs, however, because these cyanobacteria are largely unpalatable and they are not consumed by herbivores.

“Healthy food-webs are important for maintenance of species diversity and provide a source of income and food for millions of people worldwide.”

Prof Nagelkerken described understanding how eco-systems functioned in global-warming conditions as a challenge. He said that most ocean-warming research involved simplified, short-term experiments based on only one or a few species. The study is published by PLOS Biology.

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