2.3 Phytoplankton assemblages
Information of phytoplankton communities during the study period was
obtained from publicly available plankton monitoring data published by
Wasmund et al. (2017). The compiled phytoplankton data from
January through May show that the phytoplankton spring bloom in 2016
occurred almost simultaneously in the Belt Sea, Arkona Basin and
Bornholm Basin during the first half of March. The bloom was dominated
by diatoms in Kiel Bay and increasingly by Mesodinium rubrum (a
photosynthetic ciliate that relies on chloroplasts derived from its
cryptophyte symbiont (Qiu, Huang & Lin 2016)) along a western to
eastern latitudinal gradient. We compiled the relative abundance of
major algal groups based on the 10 most abundant phytoplankton taxa –
see pie charts in Fig. 1. The most noticeable trends across the
latitudinal gradient is the much greater diatom abundance in Kiel Bight
than Gdansk Basin, and vice versa for the cryptophyte group. The total
plankton production was smaller in the western than eastern sites; Kiel
Bay: 488 µg/L, Arkona Basin: 412 µg/L, Bornholm Basin: 702 µg/L, and
Gdansk Basin: 796 µg/L (averages from three cruises January-May)
(Wasmund et al. 2017).