More on Effects of Acidification

Three new studies looking at ocean acidification have shed light on some of its effects on marine organisms.

Since the beginning of the industrial revolution, human activities have accelerated the release of carbon dioxide into the atmosphere as carbon dioxide mixes with water. The two molecules combine to become carbonic acid, making seawater more acidic. As billions of molecules combine and go through this process, the overall pH of the oceans decreases, causing ocean acidification.

The first study, from Australia’s ARC Centre of Excellence for Coral Reef Studies and published Nature Climate Change, documents the the effects of rising CO2 emissions on the nervous systems of coral fishes. Based on several years of observations of how baby coral fishes react to an environment with high levels of dissolved CO2, researchers have found that elevated acidity levels directly interfere with fish neurotransmitter functions, impeding their ability to hear, smell, turn and evade predators. Prof. Philip Munday, one of the study’s authors, noted that:

“We’ve now established it isn’t simply the acidification of the oceans that is causing disruption – as is the case with shellfish and plankton with chalky skeletons – but the actual dissolved CO2 itself is damaging the fishes’ nervous systems.”

The abstract and full paper (subscription required) are available here.

Also from the ARC Centre is a new paper on the symbiotic relationship between corals and reef fishes:

“Our latest research provides strong evidence for a view that today’s coral hotspots are both a refuge for old species and a cradle for new ones,” said Peter Cowman, lead author of a recent report. “This is the first real inkling we’ve had that just protecting a large area of reef may not be enough – you have to protect the right sorts of reef.”

What constitutes the "right sort" of reef? Early coral reefs, from 300-400 million years ago, were much simpler affairs than today’s complex and colorful reefs. The real explosion of reef diversity didn’t occur until about 50 million years ago:

“When people think of coral reefs, they usually think of the beautiful branching corals like staghorn (Acropora) – well the evidence is now fairly clear that Acropora needs certain fish for it to flourish. But, it now appears that this may be a reciprocal relationship with Acropora being important for the evolution and survival of fishes on coral reefs. ”

Unfortunately Acropora corals are highly vulnerable to external impacts like Crown-of-Thorns starfish, coral bleaching, climate change and ocean acidification. Their demise will have far reaching effects on the fishes which interact with them, such as damsels, butterfly fish, cardinals and wrasses.

More details about this research can be found here, along with a citation for the original publication.

Finally we return to a recent, wide-ranging study of ocean acidification around the world using new sensors developed at the Scripps Institution of Oceanography at UC San Diego. The team measured the acidity of 15 ocean locations, including seawater in the Antarctic, and in temperate and tropical waters.

"This study is important for identifying the complexity of the ocean acidification problem around the globe," said co-author Jennifer Smith, a marine biologist with Scripps. "Our data show such huge variability in seawater pH, both within and across marine ecosystems, making global predictions of the impacts of ocean acidification a big challenge."

The study of ocean acidification on a global scale is still in its infancy, and the authors of the study note that they only made observations on coastal surface oceans, and that more research is needed in deeper ocean regions farther away from land.

With no major cuts of CO2 emissions on the horizon, more ocean acidification seems inevitable, and further research into its effects is necessary to deal with the inevitable consequences to the ecosystem that will accompany it.

UC Santa Barbara’s press release has video of the sensors deployed in some of the most remote regions of the planet, including under three meters of Antarctic sea ice.