Selective Feeding And Linkages To The Microbial Food Web By The Doliolid Dolioletta Gegenbauri

Gelatinous zooplankton play a crucial role in pelagic marine food webs, however, due to methodological challenges and persistent misconceptions of their importance, the trophic role of gelatinous zooplankton remains poorly investigated. This is particularly true for small gelatinous zooplankton including the marine pelagic tunicate, Dolioletta gegenbauri. D. gegenbauri and other doliolid species occur persistently on wide subtropical shelves where they often produce massive blooms in association with shelf upwelling conditions. As efficient filter feeders and prodigious producers of relatively low-density organic-rich aggregates, doliolids are understood to contribute significantly to shelf production, pelagic ecology, and pelagic-benthic coupling. Utilizing molecular gut content analysis and stable isotope analysis approaches, the trophic interactions of doliolids were explored during bloom and non-bloom conditions on the South Atlantic Bight continental shelf in the Western North Atlantic. Based on molecular gut content analysis, relative ingestion selectivity varied with D. gegenbauri life stage. At all life stages, doliolids ingested a wide range of prey types and sizes, but exhibited selectivity for larger prey types including diatoms, ciliates, and metazoans. Experimental growth studies confirmed that metazoan prey were ingested, but indicated that they were not digested and assimilated. Stable isotopic composition (delta C-13 and delta N-15) of wild-caught doliolids, during bloom and non-bloom conditions, were most consistent with a detrital-supplemented diet. These observations suggest that the feeding ecology of D. gegenbauri is more complex than previously reported, and have strong and unusual linkages to the microbial food web.