The Arctic Ocean (including sub-Arctic margins) is one of the fastest changing ecosystems affected by climate change. However, much remains unknown about its ecosystematic functioning, trophic interactions, and species diversity. Plankton communities have been studied to some extent, but gelatinous zooplankton (GZ; cnidarians, ctenophores, pelagic tunicates), a group that may be favoured by ocean warming, were widely neglected and only recently gained more attention. Plankton assemblages and dynamics around Iceland are well studied, while limited baseline information on GZ ecology are regionally available. In the present study, we aim to describe the seasonal changes in GZ assemblages in two North-western fjords that are representative of other fjords in Iceland. Near-surface horizontal net tows were performed regularly between April and September 2008 at five stations. In total, > 12,000 specimens of 14 species (ten hydromedusae, two scyphomedusae, one ctenophore) were collected, with peak abundances of 1937 ind. 1000 m−3 by Clytia sp. in June. The majority (10 species) of GZ was characterised by a meroplanktonic life cycle. The total abundance of GZ increased from April to June (like the species richness), while scyphomedusae and ctenophore abundances decreased towards September. The hydromedusa abundance remained high until September. While evenness and diversity indices were high in April and May, they decreased in June and remained at a lower level thereafter. Non-metric multidimensional scaling revealed that month, but not sampling station, had a significant effect on the assemblage composition, and temperature was found to have a marginally significant effect on structuring the GZ assemblage.
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© 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
- Assemblage composition
- Sub-Arctic North Atlantic