An expedition from the Hebrew University of Jerusalem and the Carnegie Institute of Science has measured a roughly 40 percent reduction in the rate of calcium carbonate deposited in Australia’s Great Barrier Reef in the last 35 years – a scenario that could damage the reef framework and endanger the world’s entire coral ecosystem.
Coral reefs are the most ecologically diverse and productive ecosystem in the ocean, with rich and diverse communities of fish, and with corals and mollusks making them a major attraction for marine and underwater tourism. Producing almost 50 percent of the net annual calcium carbonate in the oceans, corals play an important role in the global carbon cycle.
The ecological success of coral reefs depends on their calcium carbonate structures that function as a huge filter to obtain plankton – their main source of nutrition – from the open ocean. Yet recent environmental changes including coastal pollution, global warming and ocean acidification caused by high CO2 levels increasingly threaten the existence of these unique ecosystems.
“The entire coral ecosystem could collapse”
According to Prof. Jonathan Erez, one of the researchers, “The entire coral ecosystem could collapse and eventually be reduced to piles of rubble. The collapse of this habitat would ultimately lead to the loss of its magnificent and highly diverse flora and fauna.”
To better understand the effect of acidification on coral growth decline, the scientists carried out a large-scale study on the “metabolism” of corals in Lizard Island at the Great Barrier Reef in Australia.
Sign up for our free weekly newsletterSubscribe
The researchers compared calcium carbonate rates from 2008 and 2009 to those measured using similar techniques in 1975-6. Despite the fact that the coral cover remained similar, the researchers found that the recent calcification rates had decreased by between 27 percent and 49 percent. These lower rates are consistent with predictions that took into account the increase in CO2 between the two periods, suggesting that ocean acidification is the main cause for the lower calcification rate at Lizard Island.
The findings suggested that coral reefs are now making skeletons that are less dense and more fragile. While they still look the same, these coral reefs are less able to resist physical and biological erosion.
Erez and his colleague at Carnegie, Dr. J. Silverman, believe more should be done to monitor acidification of coral reefs around the world: “Routine measurements should be continued not only at Lizard Island but at other reefs around the world in order to monitor their well-being in a high CO2 world.”
Photo: Andrew K