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Mapping invertebrates

The cover and distribution of more than 25 types of benthic invertebrates from two case-study areas were modelled. Analyses show that models can be used to predict abundance and distribution of invertebrate taxa and groups and that the predictive performance does not vary substantially between the two areas.

Figure 1. Performance (mean±se) of models of invertebrates in two case-study areas using different criteria. Better performance is characterised by large r2 and AUC, but small nrmse.

Modelling abundance
The performance of models predicting abundance of invertebrates was evaluated with respect to explained variance (r2) and precision (nrmse). The proportion of explained variance in of test data were in the majority of cases statistically significant and in the range of 0.35-0.4; see Fig. 1. In terms of precision, deviations from predicted values were on average 15% of the range in examples of the Swedish-Finnish archipelago but around 10% in Lithuania (21 of 24 responses achieving nrmse values lower than 0.2, corresponding to average prediction error less than one fifth of the range of abundance values for the modeled species). Epifauna appeared to be better predicted than infauna while depositfeeding invertebrates were more difficult.

Modelling distribution
The performance of models predicting distribution (i.e. the presence vs. absence) of invertebrate species and groups in a particular site was evaluated usingh the AUC-statistic. As a rule of thumb, a value of 0.8 is often considered ”good” while 0.9 is considered excellent.

Models predicting the distribution of species and groups of species performed well in the two areas. The average AUC was as across the Baltic Sea. The average AUC was close to 0.95 in the Archipelago and 0.9 in Lithuania. Models predicting the distribution of various invertebrate species and groups of species performed well across the Baltic Sea, although invertebrates had the most spread of values of all the studied groups (invertebrates, fish and macrophytes). Both Mytilus sp. and sessile filter-feeders were modeled in both areas. They both performed well and showed no significant difference between areas.


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