Mapping the distribution of biotopes in Inner Oslo fjord

The fjord is frequently used by people for swimming, fishing and other outdoor activities, but is also under pressure due to coastal development. A sustainable management of the coastal zone and shallow areas requires knowledge of the biotopes found there. The present study was based on more than 2,000 benthic records from Bunnefjorden collected through NIVAs work for the National Council for Inner Oslofjord in the period 2005-2012. The records were sampled in the coastal zone using underwater drop-camera or ROV from 0-30 m depth, and biotopes were classified according to the Norwegian NiN system and the European EUNIS system. In the investigated area there was a total of 15 different NiN habitats, and the most common was “Naken løs eufotisk saltvannsbunn” (M15-2). The second most common was “Eufotisk normal svak energi saltvannsfastbunn” (M11-2). Through the EUNIS system a total of 23 different habitats were identified. Generalized additive models (GAM) were used to relate the distribution of the biotopes to environmental predictor variables. Probability maps were created from the models for each biotope and evaluated with independent validation data, using the area under curve value (AUC).