The invasive Pacific oyster Crassostrea gigas has since 2007 established populations in Norwegian waters. The origin of C. gigas found in Norway... » More

The invasive Pacific oyster Crassostrea gigas has since 2007 established populations in Norwegian waters. The origin of C. gigas found in Norway is unknown, but several plausible factors such as unusually warm water temperatures and persistent westerly winds during 2006 may have caused an inflow of larvae from the Danish Wadden Sea. The species is known to drastically change blue mussel beds and soft bottom areas into massive oyster reefs with negative impact on birds and other marine species as well as to human recreation areas. Hence the nature management need to monitor the development of this species and to achieve knowledge of their impact. In 2010, data on C. gigas distribution in the Oslofjord was collected and large numbers of oysters were found. Here we analyse presence-absence data with a range of predictor variables (wave exposure and sea current models, detailed digital elevation models (5 m resolution) and derived terrain attributes, to establish predictive distribution models for the species. We present an approach to select model and predictive area for the Maxent model (presence only data), and compare the results from the more traditional GAM modelling approach with similar models from Maxent and BRT.

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