RV POSEIDON Cruise Report POS473 LORELEI II: LOphelia REef Lander Expedition and Investigation II, Tromsø – Bergen – Esbjerg, 15.08. – 31.08. – 04.09.2014

As a result of the raising CO2-emissions and the resultant ocean acidification (decreasing pH and carbonate ion concentration), the impact on marine organism that build their skeletons and protective shells with calcium carbonate (e.g., mollusks, sea urchins, coccolithophorids, and stony corals) becomes more and more detrimental. In the last few years, many experiments with tropical reef building corals have shown, that a lowering of the carbonate ion concentration significantly reduces calcification rates and therefore growth (e.g., Gattuso et al. 1999; Langdon et al. 2000, 2003; Marubini et al. 2001, 2002). In the middle of this century, many tropical coral reefs may well erode faster than they can rebuild. Cold-water corals are living in an environment (high geographical latitude, cold and deep waters) already close to a critical carbonate ion concentration below calcium carbonate dissolves. Actual projections indicate that about 70% of the currently known Lophelia reef structures will be in serious danger until the end of the century (Guinotte et al. 2006). Therefore L. pertusa was cultured at GEOMAR to determine its long-term response to ocean acidification. Our work has revealed that – unexpectedly and controversially to the majority of warm-water corals – this species is potentially able to cope with elevated concentrations of CO2. Whereas short-term (1 week) high CO2 exposure resulted in a decline of calcification by 26-29 % for a pH decrease of 0.1 units and net dissolution of calcium carbonate, L. pertusa was capable to acclimate to acidified conditions in long-term (6 months) incubations, leading to slightly enhanced rates of calcification (Form & Riebesell, 2012). But all these studies were carried out in the laboratory under controlled conditions without considering natural variability and ecosystem interactions with the associated fauna. Moreover, only very little is known about the nutrition (food sources and quantity) of cold-water corals in their natural habitat. In a multifactorial laboratory study during BIOACID phase II we could show that food availability is one of the key drivers that promote the capability of these organisms to withstand environmental pressures such as alterations in the carbonate chemistry and temperature (Büscher, Form & Riebesell, in prep.). To take into account the influences of natural fluctuations and interactions (e.g. bioerosion), we aim to merge in-situ results from the two research cruises POS455 and POS473 with laboratory experimental studies for a comprehensive understanding of likely ecosystem responses under past, present and future environmental conditions