Winners and losers in a changing ocean: impact on the physiology and life history of pteropods in the Scotia Sea; Southern Ocean

The Scotia Sea (Southern Ocean) is a hotspot of biodiversity, however, it is one of the fastest warming regions in the world alongside one of the first to experience ocean acidification (OA). Thecosome (shelled) pteropods are planktonic gastropods which can dominate the Scotia Sea zooplankton community, form a key component of the polar pelagic food web and are important contributors to carbon and carbonate fluxes. Pteropods have been identified as sentinel species for OA, since their aragonitic shells are vulnerable to dissolution in waters undersaturated with respect to aragonite.

In this thesis I investigate the impact of a changing ocean on the physiology and life history of pteropods in the Scotia Sea. Firstly, I culture early stage pteropods within OA and warming conditions predicted to occur in 2100 (Chapter 2). I demonstrate that larval shell morphology and survival rates are detrimentally affected in these conditions. Secondly, I constrain the life cycle and population dynamics of pteropods collected over a year from a sediment trap deployed on a moored platform (Chapter 3). I show that Limacina helicina and Limacina retroversa both have distinct life history strategies, although, spawning of both species corresponds to phytoplankton blooms. Thirdly, I establish a baseline vertical and biogeographical distribution of pteropods using historical samples (Chapter 4). I elucidate the geographical range edges of L. retroversa and L. helicina, as well as vertical migration patterns in relation to predation threat. Finally, I examine in-situ pteropod shell condition in relation to carbonate chemistry using net and oceanographic samples collected during two recent cruises (Chapter 5). I demonstrate that larval shells are susceptible to dissolution on exposure to aragonite undersaturation, however, later life stages display some resilience, since shell dissolution is confined to breaches in the periostracum. Overall, I recommend that continued monitoring, combined with bioassays and mesocosm work, will be essential in identifying the continued threat to pteropods from rapid environmental changes.

Gardner J., 2019. Winners and losers in a changing ocean: impact on the physiology and life history of pteropods in the Scotia Sea; Southern Ocean. PhD thesis, University of East Anglia. 288 pp. Thesis.

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Ocean acidification in the IPCC AR5 WG II

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