Cold-water corals in a changing ocean: Effects on their physiological performance

Cold-water corals (CWCs) are abundant worldwide, with their distribution mainly determined by physico-chemical factors and food availability. Despite predominantly occurring in deep waters, CWC habitats are also affected by the impacts of global climate change, such as ocean acidification and warming as well as reduced primary productivity and oxygen concentration. Several previous studies have already investigated the effects of environmental changes on different CWCs species, but mainly focused on laboratory experiments under controlled conditions of a single parameter and the study of adult corals. To date, there is limited information on the effects of environmental changes on different life stages of CWCs, the combined effect of multiple factors, the impact of variable rather than constant conditions and the importance of food availability for the resilience of CWCs to environmental changes. Therefore, this thesis aimed to better understand the physiological response of CWCs to changes in their environment. In both aquarium and in situ experiments, I examined how CWCs cope with changes in single and several combined factors under stable and variable environmental conditions, taking into account the response of different life stages and the influence of differences in food availability. For this purpose, I have investigated the short- and long-term physiological response of three life stages of the CWC Caryophyllia huinayensis to different conditions of aragonite saturation (Ωarag), temperature and feeding in an aquarium experiment, all as individual factors as well as their interactions (manuscript 1). Aragonite undersaturation did not affect the corals, but elevated temperature and reduced feeding showed a clear negative effect. Juvenile and adult corals responded differently to temperature changes and reduced food supply as calcification rates of early juveniles were most affected, while adult corals showed highest mortality rates. The clear feeding effect and the delayed response of corals after more ...