Last updated March 2, 2018 at 12:34 pm
Marine wildlife may be more resilient to increasing CO2 levels in the ocean than previously thought, according to new research.
Rising carbon dioxide levels in seawater, otherwise known as ocean acidification, is a projected consequence of global warming. Previous studies have found that although elevated CO2 levels can boost growth in certain species, it can simultaneously erode resources necessary for survival.
Acidification can raise the energy cost of crucial operations, such as the production of calcium, neural functioning and acid-base regulation, all of which can profoundly affect the behaviour and resilience of corals, crustaceans and fish.
Negative outcomes overstated
However, a University of Adelaide team, led by Ivan Nagelkerken, has found that these negative outcomes may have been overstated, because experiments to discover responses to CO2 boosts have usually involved only a single species tested under laboratory conditions.
This approach, the scientists report, has resulted in simplistic results that do not take into account the complex web of complementary interactions that arise in an ocean ecosystem.
To test their hypothesis, the researchers set up a number of 1,800-litre seawater tanks, configured to reflect various habitats, each containing eight species of omnivorous and carnivorous fish and shrimps. Each tank was well supplied with natural food sources, including around 100 species of floral and faunal plankton.
Nagelkerken and colleagues then manipulated the CO2 levels and temperatures in each tank over four and a half months, cranking them up to end-of-century predicted levels.
Competition between species
What they found was intriguing. Held as individuals, fish or shrimps – known as “consumers” in the language of the experiment – were less active in foraging for food as CO2 levels rose.
In the more complex environments, however, competitive interactions arose between species, resulting in compensatory behaviours. Over all, foraging activity remained steady – and in some cases even increased. This pattern was evident regardless of the species involved.
There were, however, some downsides.
As temperatures rose risk-taking behaviours increased. Species of fish and crustaceans became more likely to hunt in open water rather than in sheltered areas, even when in some circumstances larger predators were present.
Nagelkerken and his colleagues write that their work bridges the gap between models for the direct effects of climate change and their impact on natural marine ecosystems.
The results demonstrate “the potential of ecological complexity to buffer or reverse the responses of species to future climate and mediate change or stasis in ecological communities”.
The paper was published in the journal Nature Climate Change.