Environmental drivers and zooplankton functional
composition
The environmental variables that have the potential to shape zooplankton
communities (salinity, temperature, turbidity), as well as the proxies
of eutrophication (chlorophyll a , dissolved oxygen) were not
measured consistently during the monitoring cruises. The model data are
therefore considered a realistic, and a more accurate (without
measurement error) estimate of salinity, oxygen and temperature. Oxygen,
temperature and salinity data originate from the 3D coupled sea-ice
ocean model for Baltic Sea (BSIOM; Lehmann et al. 2014), which
has a high spatial resolution (2.5 × 2.5 grid cells) and a 3 m depth
resolution for the period of 1979-2014. Oxygen concentration was
extracted from the model for the bottom layer, and salinity and
temperature were calculated as average values of water column, matching
the zooplankton observations (latitude, longitude, month). Winter air
temperatures were obtained from three weather stations in the
north-eastern part of Gulf of Riga ( Pärnu, Kihnu and
Sõrve). The Baltic Sea Index (BSI; provided by A. Lehmann,
Helmholtz Centre of Ocean Research), defined as the difference of
normalized sea level pressure (SLP) anomalies between Oslo in Norway and
Szczecin in Poland (Lehmann et al. 2002), was used as a proxy for
large-scale atmospheric variability. To investigate the potential
connections between environmental variables and zooplankton community
composition, we used a hypothesis-driven approach.