Paper Reviewed
Moulin, L., Grosjean, P., Leblud, J., Batigny, A., Collard, M. and Dubois, P. 2015. Long-term mesocosms study of the effects of ocean acidification on growth and physiology of the sea urchin Echinometra mathaei. Marine Environmental Research 103: 103-114.

Setting the stage for the report of their study of ocean acidification (OA) effects on sea urchins, Moulin et al. (2015) write that "due to their low metabolism and poor osmoregulation abilities, sea urchins have been considered as victims of OA," but they note that past studies of the subject suggest that some adult sea urchins are able to maintain the pH of their coelomic fluid when faced with a decrease of seawater pH, citing the work of Dupont and Thorndyke (2012), Stumpp et al. (2012), Calosi et al. (2013), Collard et al. (2013, 2014), Moulin et al. (2014) and Uthicke et al. (2014). However, they note that "previous studies exposed sea urchins brutally to increased pCO2 levels whereas gradual acclimatization will better mimic future OA." And they also note that in all prior studies of post-metamorphic sea urchins: (1) the algae the urchins were fed were supplied to them ad libitum, and (2) the algae had not been grown under OA conditions.

In their study, therefore, the Belgian researchers placed specimens of the sea urchin Echinometra mathaei in "replicated mesocosms provided with an artificial reef consisting of hermatypic scleractinians and reef calcareous substrate with its diverse communities of algae as principal food," after which the mesocosms experienced six months of gradual pH decrease until an OA pH level of 7.7 was reached. These conditions were then maintained for seven additional months, during which time a number of pertinent parameters were monitored, while at the conclusion of the experiment the bio-mechanical resistance of the sea urchins' skeletons was assessed.

Finally, after evaluating the many measurements they made of E. mathaei and its activities over the course of their study, Moulin et al. (2015) concluded that the urchin appeared to be resilient to ocean acidification levels expected to occur by 2100 in terms of "acid-base regulation, growth, respiration rate and test mechanical properties," all of which findings play a significant role in determining the sea urchin's interactions with both algae and corals.

References
Calosi, P., Rastrick, S.P.S., Graziano, M., Thomas, S.C., Baggini, C., Carter, H., and Spicer, J.I. 2013. Distribution of sea urchins living near shallow water CO2 vents is dependent upon species acid-base and ion-regulatory abilities. Marine Pollution Bulletin 73: 470-484.

Collard, M., Laitat, K., Moulin, L., Catarino, A.I., Grosjean, Ph and Dubois, Ph. 2013. Buffer capacity of the coelomic fluid in echinoderms. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 166: 199-206.

Collard, M., Dery, A., Dehairs, F. and Dubois, Ph. 2014. Euechinoidea and Cidaroidea respond differently to ocean acidification. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 174: 45-55.

Dupont, S. and Thorndyke, M. 2012. Relationship between CO2-driven changes in extracellular acid-base balance and cellular immune response in two polar echinoderm species. Journal of Experimental Marine Biology and Ecology 424-425: 32-37.

Moulin, L., Grosjean, Ph, Leblud, J., Batigny, A. and Dubois, Ph. 2014. Impact of elevated p CO2 on acid-base regulation of the sea urchin Echinometra mathaei and its relation to resistance to ocean acidification: a study in mesocosms. Journal of Experimental Marine Biology and Ecology 457: 97-104.

Stumpp, M., Trubenbach, K., Bennecke, D., Hu, M.Y. and Melzner, F. 2012. Resource allocation and extracellular acid-base status in the sea urchin in response to CO2 induced seawater acidification. Aquatic Toxicology 110-111: 194-207.

Uthicke, S., Liddy, M.,Nguyen, H.D. and Byrne, M. 2014. Interactive effects of near-future temperature increase and ocean acidification on physiology and gonad development in adult Pacific sea urchin, Echinometra sp. A. Coral Reefs 33: 831-845.