Indicator Evaluation and first assessment:An Example of combined Swedish-Finnish evaluation of MSTS in the Bothnian Bay and Bothnian Sea

Elena Gorokhova, Stockholm University

  1. Assessment period: 2011-2015
  2. Data origin: All stations are in the open-sea areas:
  3. Swedish National Marine Monitoring: Bothnian Bay (stations A13, A5), Bothnian Sea (stations C14, C3).
  4. Finnish Marine Monitoring: Bothnian Bay (stations Bo3, F2), Bothnian Sea (stations SR5, US5b).
  5. GES thresholds: established using Finnish data (1979-present) for the corresponding areas.
  6. Workflow
  7. Swedish data for June-September (entire time series) were used to calculate yearly averages for mean body mass (MeanSize) and total zooplankton biomass (TZB) of holoplankton (non-predatory taxa) at each station;
  8. Values for each parameter were examined (Fig. 1A) and averaged for the stations within each sub-basin (Fig. 1B); SYKE data were also plotted for comparison;
  9. The MeanSize and TZB values were compared with corresponding values in the Finnish data (assessment period 2011-2015; paired t-test; Fig. 2, p > 0.05 in all cases);
  10. As no significant differences in either MeanSize or TZB between the Swedish and Finnish data were found, they were averaged and these grand mean values were used for joint indicator assessment;
  11. This procedure resulted in the more robust MSTS values for both sub-basin, i.e. 4 stations per area instead of 2 stations that would be used in national assessment; it has not, however, affected the main outcome;
  12. Thegrand mean MeanSize and TZB values were used to calculate z-score and Lower CuSum for each sub-basin (Fig. 3).
  1. Results
  2. In the beginning of the assessment period (year 2010), the MeanSize and TZB values were in GES (Figs 1 and 3);
  3. The CuSum analysis indicated that in no case a significant deviation from the GES state was found (Fig. 3) over the entire observation period (1979-2015), including the assessment period;
  4. In the Bothnian Bay, both MeanSize and TZB values were closer to the GES threshold than in the Bothnian Sea.
  1. Conclusion: According to MSTS, pelagic food webs in the Bothnian Bay and Bothnian Sea are in-GES state.

Figure 1. Long-term trends for MeanSize and TZB in the Bothnian Bay (BB, stns A13 and A5) and Bothnian Sea (BS, stns C14 and C3) derived from Finnish data (SYKE) and Swedish data (UMF). The UMF-data are shown as station-specific trends (A) and averaged within sub-basing (B). Red line indicates GES threshold. The deviation from the GES state was tested by CuSum and found non–significant.


Figure 2. Pair-wise comparisonsfor MeanSize and TZB in the Bothnian Bay (BB) and Bothnian Sea (BS) derived from Finnish data (SYKE) and Swedish data (UMF) for 2010-2015. In no case a significant difference between the data sets was found.

Figure 3. Lower CuSums for z-scores of MeanSize and TZB in the Bothnian Bay (BB) and Bothnian Sea (BS) derived from Finnish and Swedish data combined. In all cases, the deviations from the baseline (y = 0, mean value for the reference period) have not exceeded the Lower CuSum Limits (-5σ). GES conditions are shows as green area and sub-GES are as red area.