Phytoplankton samples were always taken from fixed statutory
monitoring stations, except for the Baltic Sea, which was a combination
of fixed, and spatially scattered coastal samples (Olli et al.,
2013). Sampling frequency varied between the time series from
monthly (Patos Lagoon Estuary) to weekly or biweekly in intensively
sampled stations (e.g. in Chesapeake Bay). In regions with
strong seasonality sampling frequency was lower during winter