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Octocorals Need Not Be Overly Worried About Ocean Acidification

Paper Reviewed
Gabay, Y., Fine, M., Barkay, Z. and Benayahu, Y. 2014. Octocoral tissue provides protection from declining oceanic pH. PLOS ONE 9: e91553.

Introducing their work, Gabay et al. (2014) say that "octocorals of the order Alcyonacea are widespread throughout the tropical Indo-Pacific region and are considered the second most important benthic component after stony corals on many of these reefs," as has been reported by Sheppard et al. (1992) and Fabricius and Alderslade (2001). And they further note that "most octocorals lack a massive hard skeleton for support," explaining that "they generate hydrostatic pressure by means of internal calcite skeletal elements, termed sclerites," which they say "are found in varying densities and embedded in the fleshy coenenchyme of the colony," citing Jeng et al. (2011).

Against this backdrop, Gabay et al. "compared the effects of decreased pH on the microstructural features of both in hospite (within the colony) and isolated sclerites (in the absence of tissue protection) of the zooxanthellate reef-dwelling octocoral Ovabunda macrospiculata," colonies of which "were maintained under normal (8.2) and reduced (7.6 and 7.3) pH conditions for up to 42 days," after which "both in hospite and isolated sclerites were examined under SEM and ESEM microscopy in order to detect any microstructural changes."

The four Israeli researchers report that "no differences were found in the microstructure of the in hospite sclerites between the control and the pH treatments," but they indicate that "in stark contrast, the isolated sclerites revealed dissolution damage related to the acidity of the water."

Quoting Gabay et al., "these findings suggest a protective role of the octocoral tissue against adverse pH conditions, thus maintaining them unharmed at high pCO2,"which led them to further surmise that "in light of the competition for space with the less resilient reef calcifiers, octocorals may thus have a significant advantage under greater than normal acidic conditions."

References
Fabricius, K.W. and Alderslade, P. 2001. Soft Corals and Sea Fans: A Comprehensive Guide to the Tropical Shallow Water Genera of the Central-West Pacific, the Indian Ocean and the Red Sea. Australian Institute of Marine Science, Townsville and New Litho, Surrey Hills, Melbourne.

Jeng, M.S., Huang, H.D., Dai, C.F., Hsiao, Y.C. and Benayahu, Y. 2011. Sclerite calcification and reef-building in the fleshy octocoral genus Sinularia (Octocorallia: Alcyonacea). Coral Reefs 30: 925-933.

Sheppard, C., Andrew, P. and Roberts, C. 1992. Marine Ecology of the Arabian Region, Patterns and Processes in Extreme Tropical Environments. Academic Press, London, United Kingdom.

Posted 3 October 2014