Ocean acidification affects sharks and starfish

With rising levels of atmospheric carbon dioxide (CO2) comes ocean acidification which is disrupting the marine ecosystem. The oceans act as sinks for atmospheric CO2, and on dissolving in the ocean the CO2 lowers the pH of the water. For some time now it has been known that acidic water disrupts a specific receptor (GABAA) in the nervous system of teleost fish, and that when GABAA stops working, neuron function is impaired. Now, new studies have shown that ocean acidification can impact on members of the shark family (elasmobranchs) and on starfish (Asterias rubens).

Scientists from the Georgia Institute of Technology in Atlanta have discovered that odour-tracking behaviour in Smooth dogfish (Mustelus canis) is impaired by elevated CO2 levels. In a series of experimental studies they showed that the tracking and attacking behaviours of the sharks were significantly reduced bylevels of CO2 in the water that are consistent with climate forecasts for the mid-century and 2100. In a different study the team had previously found that fish in coral reefs where CO2 was seeping from the ocean floor were less able to detect predator odours than fish from normal coral reefs. Both of these findings suggest the potential for significant impacts on predator-prey interactions in the wild.

Starfish (Asterias rubens) from the Baltic Sea have also been found to be affected by ocean acidification, with juveniles more sensitive to the effects than adults. Researchers at GEOMAR Helmholtz Centre for Ocean Research in Kiel, found that young starfish exposed to even slightly elevated levels of CO2 in the water ate less and grew more slowly. Although the reasons behind these findings are not yet fully understood it is hypothesised that the acidic waters may affect their digestive enzymes. These starfish are one of the most important benthic predators in the ocean, particularly for regulating populations of mussels, which left unchecked can spread and outcompete other species. If starfish are affected by acidification it could have far reaching impacts on the ecosystem.

Both the shark and starfish studies were undertaken in experimental situations and authors from both papers acknowledge the need to verify their findings under more natural conditions.

 

Dixson et al. (2014). Odor tacking in sharks is reduced under future ocean acidification conditions. Global Change Biology. Doi:10.1111/gcb.12678

Photo credit Danielle Dixson

Appelhans et al. (2014). Juvenile sea stars exposed to acidification decrease feeding and growth with no acclimation potential. Mar Ecol Prog Ser 509:227-239.

 

 

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A nature writer and ecological advisor with wide experience of writing about wildlife and working in freshwater, marine and terrestrial environments. Website: www.phoebecarter.co.uk. Twitter: @DrPhoebeCarter

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