Deep-sea corals in a high CO2 ocean: behaviour, physiology and growth in Desmophyllum dianthus

Chair: Janice Lough

Fiona Murray (1)*, Sebastian Hennige (1), J. Murray Roberts (1), Eleni Anagnostou (2), Andrea Gori (1,3), Laura Wicks (1), Joseph Stewart (2), Gavin Foster (2)

1 Heriot-Watt University, Edinburgh, EH14 4AS, UK
2 National Oceanographic Centre, Southampton, SO14 3ZH, UK
3 University of Barcelona, Barcelona, 08007, Spain

Background
Anthropogenic carbon emissions causing increased ocean acidity with accompanying shifts in temperature and aragonite and calcite saturations are expected to be detrimental to marine calcifiers, and research to date has painted a bleak outlook for coral species. Colder waters, including polar and deep water are acidifying faster than other water masses, in part because CO2 dissolves more readily in colder waters, and deep-sea corals will need to adapt to ocean acidification faster than shallow species to survive into the future.

Methods
We conducted a 15 month incubation study of the responses of the cosmopolitan deep-sea coral Desmophyllum dianthus to ambient and increased CO2 (390 and 750 ppm) at 3 temperatures (7, 9 and 12 °C). Skeletal growth was determined using a 136Ba isotope tracer introduced at the start of the incubation. Feeding behaviour was recorded using time-lapse photography after 12 months. An additional 8 month incubation under the same CO2 treatments at 12 and 15 °C temperature treatments was conducted to examine calcification, respiration and ammonia secretion.

Findings
Analysis of the 15 month incubation data is at a preliminary stage but shows significant new growth based on barium analyses of the coral skeletons. Seawater acidification alone did not elicit changes in coral physiology in the 8 month exposure, however when combined with the effects of elevated temperature calcification and respiration were significantly reduced and the ratio of respired oxygen to excreted nitrogen (O:N) altered.

Conclusions
Under the combined effects of both elevated temperature and pCO2, the O:N ratio highlighted protein-dominated energy catabolism, which is much less efficient than lipid/carbohydrate catabolism. This combined with reduced respiration and calcification rates indicate that the corals are experiencing intense stress.