| Summary: | The finding of a previously undescribed cold-water coral reef (Banana Reef) in the Scottish Mingulay reef complex, with denser coverage of living Lophelia pertusa than the principal Mingulay 1 Reef, was the incentive for a comparative study of the food supply to the 2 reefs. Suspended particulate matter (SPM) samples from the surface and bottom water covering a tidal cycle were compared with respect to lipids, pigments, and delta C-13 and delta N-15. Lipid profiles and stable isotope signatures of SPM were compared with those of coral tissue samples. Concurrently, hydrographic measurements were conducted to track the movement of the water masses across both reefs. Between-reef differences in SPM lipid concentrations were small compared to those in coral tissue. Corals at Banana Reef had lower lipid concentrations, pointing to less favourable food conditions than at Mingulay 1. Stable isotopes signatures and lipid profiles showed that corals on both reefs feed primarily on surface algal matter, within the timeframe of our study. At Mingulay 1, fresh microalgae are supplied to the coral reef by local downwelling. This downwelling pulse is tidally advected to Banana Reef. Food conditions observed during this study at both reefs do not explain the between-reef difference in coral coverage. A speculative explanation for the denser coral coverage at the deeper Banana Reef encompasses the slightly lower temperature that exhibits lower metabolic stress on corals, in combination with a higher current speed and particle encounter rate.
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