Pteropod eggs released at high pCO2 lack resilience to ocean acidification

Chair: Sue-Ann Watson

Manno C. *(1), Peck V.P. (1), Tarling G.A. (1)

1British Antarctic Survey, Cambridge, Cambridgeshire, CB3 0ET, United Kingdom
*clanno@bas.ac.uk

Background
Early-life phases (fertilization, embryogenesis, larval development) are thought to be particularly sensitive to anthropogenic environmental stressors. The survivorship of embryos and larvae underpins recruitment success and factors that increase mortality and delay developmental rates in these early life-phases reducing the long-term viability of populations. The effects of Ocean Acidification (OA) on the early recruitment of Thecosome pteropods in the Southern Ocean, was investigated considering the process of spawning, quality of the spawned eggs and their capacity to develop. Since pteropods have emerged as a sentinel organism in the assessment of OA’s effect, the understanding of the early developmental phase of their life-cycle is a crucial issue to investigate.

Methods
Maternal OA stress was induced on female pteropods (Limacina helicina antarctica) through exposure to present day pCO2 conditions and two potential future OA states. The eggs spawned from these females, both before and during their exposure to the OA, were incubated themselves in this same range of conditions.

Findings
Maternal OA stress resulted in eggs with lower carbon content, while embryonic OA stress retarded development. The combined influence of OA stress on both, egg-brood and embryonic development phase (maternal plus embryonic OA stress) reduced the percentage of eggs successfully reaching the organogenesis by 80%. We propose that OA stress not only affects the somatic tissue of pteropods but also their gonadic functional capabilities. The interaction of these processes with pteropod vertical distribution, was examined. We found adults at depths of up to 600 m, which will result in them experiencing OA conditioned water, from the rapidly shallowing aragonite lysocline in the Southern Ocean, long before the previously assumed date of around 2030.

Conclusions
These findings indicate that OA will have a severe impact on pteropod recruitment and the maintenance of viable populations in Polar Regions, even within the coming decades.