The effect of climate change on Southern Ocean benthic calcifiers

Abstract

Southern Ocean (SO) warming has been increasing in the last decades and it is expected to continue, which will cause ice loss and changes in the food web. Similarly, short undersaturation events are projected from 2030 onwards. Antarctic organisms, and especially those with shells, are expected to be one of the most affected by climate change, and therefore there is an importance to assess if different environmental conditions lead to changes in the shell structure specifically in ontogeny, size, integrity, and geochemistry. The Southern Ocean has many different types of natural environmental, which makes it an ideal place to test the responses of species with different lifestyles (infaunal and epifaunal). In the Amundsen Sea, there are warmer waters with the carbonate undersaturated Circumpolar Deep Water upwelling onto the shelf. In contrast, the Weddell Sea is a region of colder down-welling water masses. North to the Weddell Sea, South Sandwich Islands present high productivity compared with the other two SO regions. Further north of the Polar Front, the Magellan region has high temperatures and aragonite saturation. The results show that Dentalium majorinum, Limopsis marionensis and Cyclocardia astartoides present different morphologies in the different regions. D. majorinum and C. astartoides specimens from the Weddell Sea are larger than those from Amundsen Sea. Likewise, larger specimens were found on South Sandwich Island for L. marionensis individuals, all of these in areas of higher productivity. The variability between the different regions of the studied species suggests a plastic morphology, which can help them compensate for environmental changes. Finite element analysis (FEA) revealed that the shape (curvature) and length increase the risk of breakage under hydrostatic pressure load whilst ornamentation (number of ribs) enhance the shell strength under drag flow. Age determination of D. majorinum (23 years) and C. astartoides (25 years) are in accordance with others although they need to be taken with caution. In the three species studied, the density of the shell and the geochemistry do not show great differences between regions, except for L. marionensis, which has a higher density at the north of the Polar Front. This suggests a high biomineralization control. All collected specimens show different levels of dissolution, suggesting that they are compensating for environmental pressures. All analysed specimens were collected alive, which suggest that they are currently coping with the environmental pressures. Nevertheless, as the Southern Ocean continues to become warmer and undersaturated, a continued assessment is necessary.

Date of Award	29 Sept 2020
Original language	English
Awarding Institution	University of Bristol
Supervisor	Daniela N Schmidt (Supervisor), Katrin Linse (Supervisor) & Emily J Rayfield (Supervisor)