Sea Cucumber poo moderates impact of ocean acidification on coral reefs

Ocean acidification is a major threat to coral reefs and other marine zooplankton and creatures using calcium carbonate shells. Marine and Climate scientists working at the University of Sydney's research station, One Tree Island, on the Great Barrier Reef have discovered that sea cucumber poo increases the alkalinity of the reef water providing a buffer to the increasing acidity caused by ocean acidification.

It is a vital marine process that provides some buffer to corals with the impacts of ocean acidification. "We have found that sea cucumbers play a vital role in reducing the harmful impact of ocean acidification on coral growth," said Professor Maria Byrne, the director of One Tree Island Research Station.


"When they ingest sand, the natural digestive processes in the sea cucumber's gut increases the pH levels of the water on the reef where they defecate, countering the negative effects of ocean acidification," said Professor Byrne.

The sea cucumbers digest sand and excrete Calcium carbonate (CaCO3), a key component for corals to build their fantastic structures. Coral reefs need to accumulate CaCO3 at a rate greater than or equal to the CaCO3 that is continually being eroded from the reef.

"The research at One Tree Island showed that in a healthy reef, dissolution of calcium carbonate sediment by sea cucumbers and other bioeroders appears to be an important component of the natural calcium carbonate turnover," said Professor Byrne.

"The ammonia waste produced when sea cucumbers digest sand also serves to fertilise the surrounding area, providing nutrients for coral growth," she added.

Sea cucumbers are among the largest invertebrates found on tropical reefs. Some 30 species are commercially harvested by the fishery industry along the Great Barrier Reef and throughout the tropics.

"We urgently need to understand the impact of removing sea cucumbers and other invertebrates on reef health and resilience at a time when reefs face an uncertain future," Professor Byrne said.

Of course coral reefs are being subject to a range of stressors, of which ocean acidification is just one. Increasing sea surface temperatures, pollution from human development and agricultural runoff, and commercial fishing all impact coral reef ecosystems. Increased sea surface temperatures (SST) caused mass coral bleaching events across the Great Barrier Reef in the summers of 1998, 2002 and 2006.

Sources:

• Adapted from Sydney University News, January 30, 2012 - Sea cucumbers could be key to preserving coral reefs
  
• Kenneth Schneider, Jacob Silverman, Erika Woolsey, Hampus Eriksson, Maria Byrne, Ken Caldeira, JOURNAL OF GEOPHYSICAL RESEARCH, 23 December 2011 - Potential influence of sea cucumbers on coral reef CaCO3 budget: A case study at One Tree Reef (abstract) doi:10.1029/2011JG001755
  
• Image of Sea Cucumber by clamabue on Flickr. Creative Commons Attribution 2.0 Generic (CC BY 2.0)