Feeding Ecology of Three Myctophid Species at the Great Meteor Seamount (North-East Atlantic)

The feeding ecology of three abundant myctophid species was studied using individuals sampled at the Great Meteor Seamount during a cruise of RV "Meteor", M42/3, in September 1998. Different habitats defined by water depth were sampled with a pelagic trawl: the north-eastern and the south-western slopes of the seamount (bottom depths between 300 and 1500 m), and an oceanic deep-water station (bottom depth > 2300 m). The food composition of the three myctophids was analysed and showed interspecific differences. The diets of the larger myctophid species, Ceratoscopelus warmingii (standard length 20 to 76 mm) and Hygophum hygomii (SL 29 to 63 mm), were dominated by amphipods. In contrast, the major prey categories of the smaller sized myctophid Lobianchia dofleini (SL 21 to 34 mm) were ostracods and calanoid copepods. We found a shift in prey composition of C warmingii with predator size. Individuals larger than 40 mm standard length fed on a higher proportion of amphipods and on a lower proportion of pteropods compared to smaller sized individuals. Comparison of the myctophid diets with zooplankton composition in multi-net samples showed that the examined species consume selected prey categories in disproportionate numbers to their environmental abundance. L. dofleini showed a pronounced selectivity for the copepod species Pleuromamma xiphias. The observed differences in the dietary compositions of C.warmingii and H. hygomii at different localities of the seamount was a result of local predator size variability rather than an effect of local food availability. Feeding intensity of the myctophids was enhanced over the seamount slopes compared to ail oceanic reference station. This could be due to more favourable feeding conditions over the seamount slopes, where hydrographic conditions were characterised by enhanced turbulent mixing processes.