Marine Food Web Study Raises Climate Change Concern

A new Australian study has found that levels of commercial fish stocks could be harmed as rising sea temperatures affect their source of food.

A team of University of Adelaide scientists has demonstrated how climate change can drive the collapse of marine food webs, showing that increased temperatures reduce the vital flow of energy from the primary food producers at the bottom (e.g. algae), to intermediate consumers (herbivores), to predators at the top of marine food webs.

Such disturbances in energy transfer can potentially lead to a decrease in food availability for top predators, which in turn, can lead to negative impacts for many marine species within these food webs.

“Healthy food webs are important for maintenance of species diversity and provide a source of income and food for millions of people worldwide,” said lead author PhD student, Hadayet Ullah. “Therefore, it is important to understand how climate change is altering marine food webs in the near future.”

Twelve large 1,600 liter tanks were constructed to mimic predicted conditions of elevated ocean temperature and acidity caused by increasing human greenhouse gas emissions. The tanks housed a range of species including algae, shrimp, sponges, snails and fish.

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 then used these measurements in a sophisticated food web model.

“Whilst 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.”

Marine ecosystems are already experiencing major impacts from global warming, and Ullah believes it is vital to gain a better understanding of how these results can be extrapolated to ecosystems worldwide. Most research on ocean warming involves simplified, short-term experiments based on only one or a few species. “If we are to adequately forecast the impacts of climate change on ocean food webs and fisheries productivity, we need more complex and realistic approaches that provide more reliable data for sophisticated food web models,” said project leader Professor Ivan Nagelkerken.