ALBERT

Description: The scleractinian coral Lophelia pertusa (Caryophylliidae) is the most common frameworkforming cold-water coral with a global distribution. L. pertusa bioherms are hot-spots of biodiversity because their three-dimensional framework provides niches and nursery grounds for a variety of species, including commercially important fish species. In contrast to shallowwater corals from the tropics, very little is known about the ecophysiology of cold-water corals such as L. pertusa and their sensitivity towards climate change. The present study intends to start filling this knowledge gap by examining a variety of L. pertusa’s ecophysiological responses (e.g. food uptake, respiration, growth, fitness, behaviour) under present-day (in the following referred as “ambient”) and experimentally manipulated environmental conditions. Living specimens of L. pertusa from two Norwegian cold-water coral locations (Oslofjord and Sula Reef Complex) were collected during two research cruises with the aid of the manned submersible JAGO and transferred into a newly established closed recirculating system at IFM-GEOMAR. Long-term analyses (〉3 years) of dissolved inorganic nutrients revealed the high tolerance of L. pertusa to rising concentrations of nitrate and phosphate. However, for the main toxic compound - ammonium - it could be demonstrated that the corals’ polyp behaviour alters if concentrations are increased to 〉 17 μmol L-1. Food availability is thought to be one of the most important factors determining cold-water coral distribution and growth. This study provides feeding rates for three live food organisms encompassing different sizes and qualities. It also describes the food uptake mechanism for mesozooplankton based on the first video documentation of the whole feeding process. The effect of rising temperatures (ocean warming) on the oxygen consumption, fitness, and behaviour was investigated through a combination of short-term and long-term aquarium experiments. This study shows that at ambient conditions of 7.5 °C L. pertusa exhibits low respiration rates of ~ 0.3 μmol O2 g-1 h-1 which may increase up to 58 % after a relatively small temperature change (+ 3.5 °C). High Q10 values of 3.7 ± 0.7 in these corals and significantly depressed RNA/DNA ratios in coral polyps maintained for 2 weeks under elevated temperatures (11°C) revealed that L. pertusa is sensitive to small temperature changes even though analyses of their behaviour may suggest some acclimatisation. L. pertusa exhibits relatively low bulk calcification rates that vary over time and applied measurement methods. On average calcification amounts to 8.7 x 10-3 % d-1 which is intermediate in the broad range of reported L. pertusa growth rates. Interestingly, corals fed under nearby ad libitum conditions showed no relationship between food quality/quantity and growth. This indicates a degree of regulation in the feeding mechanism and may suggest that calcification is rather dependent on a basic metabolic rate than on specific food supply. The impact of increasing concentrations of CO2 (ocean acidification) on L. pertusa growth rates and fitness was examined in a short-term (one week) and a long-term (8 months) experiment. This study shows for the first time that - when kept under long-term exposure to elevated CO2 levels - L. pertusa is capable to compensate for adverse effects as experienced during short-term incubations. Net growth is sustained even in waters undersaturated with respect to aragonite (ΩAr 〈 1). These results suggest that cold-water coral reefs, the majority of which will be exposed to undersaturated waters before the end of this century, may not suffer immediate wide-spread extinction as previously projected. However, the fact that even a temperature increase of about 3 °C seems to be of higher relevance in respect to fitness than a doubling of the pCO2 emphasises the problem of synergistic impacts between ocean warming and ocean acidification and the need for further long-term incubation experiments.