Identifying high-density areas of oysters using species distribution modeling: Lessons for conservation of the native Ostrea edulis and management of the invasive Magallana (Crassostrea) gigas in Sweden

Aim Understanding spatial patterns of the distribution of adult native oyster, Ostrea edulis, and the invasive Magallana (Crassostrea) gigas is important for management of these populations. The aim of this study was to use ensemble SDM's to (a) identify and predict conservation hotspots, (b) assess the current level of protection for O. edulis, and (c) quantify the amount of overlap between the two species where interactions with M. gigas are most likely. Location Skagerrak, Sweden. Methods We used data collected by video at depths from 0.5 to 10 m in 436 sites. Models of occurrence and densities >1 m(-2) were fitted and assessed using ensemble methods (biomod2 package). Models of high-density hotspots were used to predict, map, and quantify areal extent of the species in order to assess the degree of overlap with protected areas and the potential for interactions between the two species. Results Both species were widely distributed in the region. Observations of high-density habitats, mainly occurring at depths of approximate to 3 and 0.5 m for O. edulis and M. gigas, respectively, were found in 4% and 2% of the sites. Models provided useful predictions for both species (AUC = 0.85-0.99; sensitivity = 0.74-1.0; specificity = 0.72-0.97). High-density areas occupy roughly 15 km(2) each with substantial overlap between species. 50% of these are protected only by fisheries regulations, 44% are found in Natura 2000 reserves and 6% of the predicted O. edulis enjoys protection in a national park. Main conclusions Data collection by video in combination with SDM's provides a realistic approach for large-scale quantification of spatial patterns of marine population and habitats. O. edulis and M. gigas are common in the area, but a large proportion of the most valuable O. edulis habitats are not found in protected areas. The overlap between species suggests that efforts to manage the invasive M. gigas need to be integrated with management actions to conserve the native O. edulis.

Automated summary

Understanding spatial patterns of native oyster and invasive oyster distribution is crucial for effective population management. This study used ensemble SDM models to identify conservation hotspots, assess protection levels, and quantify species overlap. Results show widespread distribution of both species, with high-density habitats identified, highlighting the need for integrated conservation efforts.