Thresholds and Status evaluation

The indicator and some of its associated threshold values are still being tested in some countries.

Further development may be necessary to make the indicator suitable in all subbasins. The current results should thus to be considered as intermediate.

 

Thresholds values have been set using two different approaches, dependent on which method for species sensitivity values was used. The threshold value concept is a defined value that should be achieved in order to indicate good status (Thresholds figure 1).

Softbottom macrofauna Thresholds figure 1.png 

Thresholds figure 1. Schematic figure of the threshold value concept applied in the core indicator.

 

In  Bothnian Bay, The Quark, Bothnian Sea, Åland Sea, Northern Baltic Proper and Western Gotland Basin, where the method follows Leonardsson et al. (2009), the Swedish intercalibrated BQI good-moderate threshold values, developed for outer coastal waters under the EU Water Framework Directive, are considered to also be applicable for the open sea assessment units. The establishment of these threshold values is based on both statistical tests and expert judgment, using data from areas without local disturbance to define high and good status as baselines, as described in Leonardsson et al. (2009).

In Gulf of Finland, Gulf of Riga, Eastern Gotland Basin, Bay of Mecklenburg and Kiel Bay the threshold is defined based on methods described in Schiele et al. (2016). In this method the described fauna sub-sets that occur in the assessment unit are first identified. Threshold values are then calculated for each subset according to a pragmatic statistical scheme developed by Perus et al. (2007) and later modified during an intercalibration process, as described by Carletti & Heiskanen (2009). In short, this method sets threshold values as 0.6 times the 10th percentile of the top 10 % of all index values within a subset.

Threshold values for all open sea assessment units are shown in Thresholds table 1.


Thresholds table 1. Threshold values used in the open sea assessment units. In Bothnian Bay, The Quark, Bothnian Sea, Åland Sea, Northern Baltic Proper and Western Gotland Basin one threshold value per unit is given, whereas in Gulf of Finland, Gulf of Riga, Eastern Gotland Basin, Bay of Mecklenburg and Kiel Bay one threshold value per subset, irrespective of assessment unit is given. Thus one assessment unit may have more than one threshold value. Note that threshold values in assessment units where the Schiele et al. (2016) sensitivity value method is used will be 0.5 after normalisation to a common scale (see Assessment protocol).

Softbottom macrofauna Table 1.png


No threshold value has been agreed for the following open sea assessment units: Kattegat, Great Belt, the Sound, Arkona Basin, Bornholm Basin and Gdansk Basin. The indicator is in principle applicable in these areas, and further work for these assessment units is underway.