Researchers at the University of South Adelaide in South Australia have constructed a three-level “food web” (the way in which food-chains interconnect) to illustrate how ocean acidification combined with warmer sea temperatures could destroy marine biodiversity over the next century.
The study is claimed to be the most comprehensive yet in terms of how global-warming affects multiple layers of an eco-system as opposed to individual species.
Prof Ivan Nagelkerken’s team used twelve 2000-litre aquaria filled with imitation seagrass, open sand and rocky reef habitats to simulate real-world environments. Plants such as algae, small invertebrates to graze on the plants and fish to prey on the invertebrates were provided to complete the food web. Artificial tidal movements took the form of circular currents.
The food webs were exposed to the levels of ocean acidification and warming predicted for the end of the century, and over several months the scientists observed processes such as predation and organism growth.
They found that the ocean acidification caused by the high carbon-dioxide levels expected by century's end would actually provide a “fertilising effect”, boosting production at different levels of the food web.
However, this benefit would be cancelled out by the overwhelming stress caused to marine animals by ocean-warming, preventing them from using the increased resources efficiently for their own growth and development. With the fragile relationship between predators and prey thrown off balance, a food-web collapse would result.
“Both acidification and warmer oceans are indirect results of human CO2 emissions into the atmosphere,” said Prof Nagelkerken – according to NASA, CO2 levels in the air are the highest they have been in 650,000 years. He said that protection of hard-hit natural habitats such as the Great Barrier Reef needed to be prioritised to help slow climate-change effects.
With the acidification of oceans and average temperatures rising up to half a degree in some areas, Prof Nagelkerken said that: “The consequences for marine eco-systems are likely to be severe – oceans in the future may provide less fish and shellfish for us to eat.
“Obviously more work needs to be done but once you have more information about the effects of all these stressors, human and environment, you can identify which species and which habitats need most protection, then develop appropriate mitigation strategies and conservation efforts.”
The report is published in Global Change Biology.
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