Florian Lüskow

Gelatinous zooplankton (GZ, i.e. primarily pelagic cnidarians, tunicates and ctenophores) play important roles in a variety of aquatic food webs, such as being keystone predators, competitors, food resources or vectors for parasites and inhabit most marine ecosystems around the globe. There is growing discussion about increasing abundances of GZ, however, it is unclear whether the piling up sightings are due to growing awareness, true increasing trends or part of long-term oscillations. Since the 1980s studies on standings stocks, production and feeding rates of GZ were conducted in British Columbian waters, primarily focusing on ctenophores, scypho- and hydromedusa. But for a more holistic understanding of the trophodynamic ecosystem functioning, it is essential to add knowledge on gelatinous herbivores, such as salps, doliolids, larvaceans and pyrosomes. Recent bloom incidents of pyrosomes in waters of British Columbia and northwestern US (summer 2017) increased awareness of these often overlooked GZ species. Therefore, we suggest studying the pelagic community composition in combination with population dynamics of GZ, prey species, potential competitors (larval fish) and hydrographic parameters at several stations along a coast-offshore transect in the course of one year using plankton net tows and an analytical approach (e.g. eDNA analysis). Specimens of all taxa collected during cruises will be used for analyzing diets to draw conclusions regarding interactions between groups on same and different trophic levels also under temporal change. Out-migrating juvenile salmonids and small pelagic fishes may interact in the coastal zone with GZ in various ways. For quantification predatory (in case of ctenophores, siphonophores and medusae) and grazing (in case of pyrosomes and salps) impacts on lower trophic levels, we suggest laboratory feeding experiments using cultured organisms as prey. With the new knowledge about population sizes, distributions and dynamics, feeding rates and species-specific diets, it will be possible to access how GZ is affecting lower trophic levels that are simultaneously exploited by commercially important fish species in coastal British Columbian waters.