To endure, coral reefs must accumulate CaCO₃ at a rate greater or equal than the sum of mechanically, biologically and chemically mediated erosion rates. We investigated the potential role of holothurians on the CaCO₃ balance of a coral reef. These deposit feeders process carbonate sand and rubble through their digestive tract and dissolve CaCO₃ as part of their digestive process. In aquarium incubations with Stichopus herrmanni and Holothuria leucospilota total alkalinity increased by 97 {plus minus} 36 and 47 {plus minus} 18μmol kg^-1, respectively. This increase was due to CaCO₃ dissolution, 81 {plus minus} 34 and 34 {plus minus} 16μmol kg^-1 and ammonia secretion, 16 {plus minus} 4 and 14 {plus minus} 4μmol kg^-1, respectively for these species. Surveys conducted at a long term monitoring site of community calcification (DK13) on One Tree Reef indicated that the density of sea cucumbers was ca. 1 individual m^-2. We used these data and data from surveys at Shark Alley to estimate the dissolution of CaCO₃ by the sea cucumbers at both sites. At DK13 the sea cucumber population was estimated to be responsible for nearly 50% of the nighttime CaCO₃ dissolution, while in Shark Alley for most of the nighttime dissolution. Thus, in a healthy reef, bioeroders dissolution of CaCO₃ sediment appears to be an important component of the natural CaCO₃ turnover and a substantial source of alkalinity as well. This additional alkalinity could partially buffer changes in seawater pH associated with increasing atmospheric CO₂ locally, thus reducing the impact of ocean acidification on coral growth.

Schneider K., Silverman J., Woolsey E., Eriksson H., Byrne M., & Caldeira K., in press. Potential influence of sea cucumbers on coral reef CaCO3 budget: a case study at One Tree Reef. Journal of Geophysical Research doi:10.1029/2011JG001755. Article (subscription required).