Soft echinoderms to be expected in the future? Impact of ocean acidification on the mechanical properties of the skeleton and underlying mechanisms

Chair: Janice Lough

Dery, Aurélie (1), Marie Collard (1), Philippe Dubois (1)

1 Université Libre de Bruxelles, B-1050 Bruxelles, Belgium

Background
Since the Cambrian, formation of hard skeletons as a response to predation played a major role in the evolution of marine organisms. Ocean acidification has been reported to negatively impact the skeletal growth in calcified marine organisms and to induce dissolution of the skeleton even in living specimens, possibly jeopardizing its functions. However, in most cases, the functional mechanical impact of these effects is poorly known and appears to differ according to the considered taxa. Therefore, we determined the effects of ocean acidification on the mechanical properties of the skeleton in different echinoderm taxa and investigated the underlying mechanisms.

Methods
Specimens from different short and long term acidification experiments as well as field specimens collected along natural pH gradients generated by CO2 vents were used. Measurements were carried out on selected isolated ossicles using 2 or 3 points- bending tests.

Findings
Significant effects may even be recorded at short term (<1 month). Impact differed according to taxa but also within the same individual, spines being more affected than the test in sea urchins for instance. The breaking force of sea urchin spines was reduced by up to 50% at low pH. In some taxa, the Young’s modulus was increased, indicating a higher stiffness (probably responsible for the higher brittleness).

Conclusions
The defensive function of spines in some sea urchin taxa is affected and may result in increased predation. Effects could to be linked to the acid-base physiology of the considered species.