Food web structure and trophodynamics of deep-sea plankton from the Bari Canyon and adjacent slope (Southern Adriatic, central Mediterranean Sea)

Zooplankton represent a key component of deep-sea ecosystems, linking Particulate Organic Matter (POM) to higher trophic levels through both vertical migrations from the photic zone and being prey of several megafaunal species, including demersal and benthopelagic organisms. Nevertheless, this key group in deep-sea ecosystems is far to be well known, especially concerning trophic aspects. In this study, we aimed to depict the trophic web structure of deep-sea zooplankton collected in sediment traps from the Southern Adriatic, central Mediterranean Sea, and adjacent slope from 600 to 1200 m, and its trophodynamics. To achieve these objectives, we considered a long time-series set of samples, from March 2010 to October 2012 and we used stable isotope analysis of nitrogen and carbon. The area is characterised by cascading events of dense shelf waters, and the possible influence of this periodic phenomenon on seasonal changes in the isotopic composition of deep-sea zooplanktonic species was also analysed. Our results evidenced a complex structure for the deep-sea zooplankton food web with taxa organized in three trophic levels from POM feeders to ultra-specialized carnivores. Temporal changes in the isotopic signatures of deep-sea zooplankton species were observed, although the influence of cascading events was not so clear. The high swimming capability of deep-sea zooplankton and their ability to perform vertical migrations may be the cause of such unclear relationship, with species more relying on vertical fluxes from surface primary production than on lateral advective transport of organic particles.