In October 2020, the mud blister worm Polydora websteri was observed for the first time in Sweden (genetically verified), in a natural Pacific oyster bed (Crassostrea gigas) close to Lysekil on the Swedish west coast. The worm is a known invader, originating from Asia but has spread to many parts of the world, resulting in major negative effects for the aquaculture industry. The worm does not primarily kill the host but will produce dark blisters inside the oyster shell that contain anoxic sediment, making them less attractive for human consumption (see photo). The first European findings were recorded near the island Sylt in 2014 near an oyster production site, and have been recorded at several sites in the Netherlands since then.
Despite several scientific papers stating that the worm can infect multiple bivalve species, we have not found any infection in the native oysters or mussels in Sweden yet based on initial surveys (or any genetically verified data showing this). However the authorities in Sweden are worried that the species may infect the native oysters. Therefore, we want to find out if anybody has found P. websteri in Ostrea edulis or other native bivalve species (apart from C. gigas). Note that there are other Polydora species that can infect oysters too, but not forming distinct dark mud blisters (photo). Please contact us if you have any relevant information. Thank you: anna-lisa.wrange@ivl.se