O-18/O-16 and C-13/C-12 in an ahermatypic deepwater coral Lophelia pertusafrom the North Atlantic: a case of disequilibrium isotope fractionation

The numerous stable isotope studies of scleractinian photosynthetic reef-bu ilding corals in tropical seas have demonstrated the complexity of the biol ogical and environmental factors that give rise to their isotopic compositi on. Scleractinian non-photosynthetic corals of the deep cold water environm ent might be expected to reflect the more stable physical environment in th e deep sea, However, in comparison, little is known about their isotope sys tematics. The present study concentrates on specimens of Lophelia pertusa f rom the north-eastern Atlantic, the Norwegian Shelf and Fjord, Aliquots tak en from the theca represent time series and show variations in delta(13)C a nd delta(18)O of up to 4.7 and 2.4 parts per thousand, respectively. The va riations seem to be related to morphological features of branching. The ten dency of higher values near the tip of the polyps reported previously was d etected only in some samples. The delta(18)O of the corals are in all cases more negative than the equilibrium values. There is a strong correlation b etween delta(13)C and delta(18)O forming linear arrays. The difference betw een these arrays is more pronounced in delta(13)C, The covariation of delta (13)C and delta(18)O indicates an overruling 'kinetic isotope effect'. This is in line with the behaviour of some trace elements. This isotope effect should he regarded as one manifestation of variations in partition coeffici ents dictated by a biological control on mineralisation (such as food or re production) rather than changes in the relative contribution of metabolic c arbon affecting delta(13)C, and changes in temperature affecting delta(18)O . Copyright (C) 2000 John Wiley & Sons, Ltd.