Brachiopod tolerance: shell structure and composition are not affected by ocean acidification

Chair: Sue-Ann Watson

Cross, E.L (1,2)*, Peck, L. S. (1), Harper, E. M. (2)

1 British Antarctic Survey, Cambridge, CB3 0ET, UK
2 Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, UK

Background
Surface seawaters are being modified in the current rapid environmental change due to excess carbon dioxide. Marine calcifiers are thought to be the most vulnerable organisms to ocean acidification due to the reduction in the availability of carbonate ions for shell production. Brachiopods inhabit all of the world’s oceans and are possibly one of the most calcium carbonate dependent organisms as >90% of their dry mass resides in their skeleton. Little is known, however, about the effects of lowered pH on these taxa.

Methods
A polar (Liothyrella uva) and a temperate (Calloria inconspicua) brachiopod were cultured under future projected environmental conditions in separate CO2 perturbation experiments for 7 months and 3 months, respectively. Shell characteristics were analysed to determine the effects of ocean acidification on shell production and maintenance.

Findings
Lowered pH did not affect shell growth rates, ability to repair shells, punctae (shell perforations) densities, crystal morphology, elemental composition and total shell thickness in both species. Shell dissolution increased with decreasing pH in both species, with more extensive dissolution in the cold-water L.uva. This trend correlated with a decrease in the primary layer and an increase in secondary layer thickness in L.uva. The less extensive dissolution in C.inconspicua is reflected in the unaffected primary and secondary layer thickness with decreasing pH.

Conclusions
Both species will continue to produce the same shell structurally and elementally under predicted end-century environmental conditions. C.inconspicua will be able to maintain shell integrity in the coming decade as only slight dissolution occurred and this did not affect the thickness of the shell. Shell structure can be maintained in L.uva with the production of a thicker secondary layer offsetting primary layer dissolution. The ability of both these brachiopods to continue shell production and maintenance suggests that both species have a robust control over calcification processes