Molecular Assessment of Salp Gut Content - an improved method to determine phytoplankton biodiversity in the Southern Ocean?
Final Report Abstract
In the current project we formulated the hypothesis, that the “analysis of salp gut content could provide an integrated signal of phytoplankton diversity”. This hypothesis was tested with leftover samples from the Lazarev Krill Study (LARKRIS) where for the salp species I. racovitzai a seasonal data set and for S. thompsoni a data set with a large spatial distribution from one season was available. To study this hypothesis we used different molecular methods to assess the phytoplankton composition in the gut content of both salps. This involved different molecular fingerprinting methods such as Automated Ribosomal Intragenic Spacer Analysis (ARISA) and Terminal Restriction Length Polymorphism (T-RFLP) accompanied by 454-pyrosequencing of the 18S rDNA V4 region. This approach provided us with detailed high resolution information on the overall species composition in the gut content of the salps. In contrast to the assumption, no clear seasonal cycle of the ingested phytoplankton was found in the salp species I. racovitzai. The ARISA clusters of the salp S. thompsoni could also not be assigned to any environmental data. We therefore have to withdraw from our original approach to use salps as an integrative phytoplankton sampler to determine the biodiversity of phytoplankton in the Southern Ocean. However, a strong difference particular in the group of Dinoflagellates was observed between the two species, which suggest different ecological niches for this co-occurring species in the Lazarev Sea. The observations are in good agreement with previous performed fatty acid analyses, where the observed group displayed similar results. Particular the high occurrence of dinoflagellates reads in our study reveals, that this group has been overlooked in previous studies and might be an important food source for salps in the Southern Ocean.
