New research by Prof. Yehuda Benayahu, Dr Zehava Barkay, Professor Maoz Fine, and their jointly supervised graduate student Yasmin Gabay of Tel Aviv University's Department of Zoology, Wolfson Applied Materials Research Center and the Interuniversity Institute for Marine Sciences in Eilat has uncovered the protective properties of soft coral tissue, which proved resilient when exposed to declining oceanic pH levels.
The study, published in PLOS One, provides insight into the changing face of coral reefs threatened by dropping oceanic pH levels and may provide a new approach toward preserving the harder, calcified reef foundations.
Reefs and environmental change
Acidification is caused by increased carbon dioxide emissions in the atmosphere due to global change, fossil fuel burning, and other pollution. These emissions dissolve in the ocean, resulting in a slight lowering of oceanic pH levels.
This produces changes to ocean water's carbon content, destroying the calcification of reef-building stony coral.
"The rise in temperature and ocean acidification are the main concerns of environmental change," said Professor Benayahu, the Israel Cohen Chair in Environmental Zoology, whose TAU laboratory is home to one of the world's only soft coral (octocoral) research centers.
"We know the value of reefs, the massive calcium carbonate constructions that act as wave breakers, and protect against floods, erosion, hurricanes, and typhoons. While alive, they provide habitats for thousands of living organisms, from sea urchins to clams, algae to fish. Reefs are also economically important in regions like Eilat or the Caribbean."
At first, the researchers examined the effects of lowered pH levels on living colonies of soft corals. Observing no significant effects on their physiology, Gabay thought it would be interesting to consider the effects of acidification on the skeleton of these soft corals.
"We really wanted to know if something could survive dropping pH levels in the future," said Gabay.
"I was curious as to whether coral tissue could protect the inner coral skeleton, which is of most use in terms of reef construction, so I conducted an experiment using live soft corals and soft coral skeletons, which were placed in tanks containing ocean water with manipulated pH levels."
Using state-of-the-art microscopy, Gabay then scanned the tissue-covered skeletons and bare skeletons of soft corals exposed to experimental acidic conditions, the same conditions the International Panel of Climate Change predicts will occur 100 years from now if CO2 emissions continue to rise. She found that the bare soft coral skeletons exhibited acidic stressed symptoms – large pockets burned into their microscopic corpuscular subunits – whereas the tissue-covered skeleton revealed almost no damage to its microscopic subunits.
"We found that the soft coral's tissue may indeed protect the skeleton from declining pH levels," said Yasmin Gabay.
"The organism's internal environment apparently has a mechanism that protects against the acidic conditions."