Towards evidence- based dynamic management of coastal bivalves

In less than a decade, the Pacific oyster (Magallana/Crassostrea gigas) went from being a species only known by oyster enthusiasts to one of the most prominent and divisive invasive species in Scandinavian waters (Laugen et al 2015). It creates havoc at popular recreational beaches, has been labelled as the one of the main causes of the recent decline in blue mussel (Mytilus edulis) stocks, and is suggested to be a threat to the last remaining wild stocks of the European flat oyster (Ostrea edulis). While the first accusation is undoubtedly true, particularly in areas where Pacific oysters are now well established, there is a conspicuous lack of evidence to support the others. Thus, management decisions are being made, and tax-payer money spent, without the necessary scientific background.

The Laugen Lab at CCR is part of a Scandinavian network of researchers, natural resource managers, and industry partners working towards solving some of the management challenges induced by the Pacific oyster invasion. By developing a dynamic management model that tailors management actions to local conditions, we aim at balancing stakeholder interests, including those that see the Pacific oyster as a valuable resource. We do this by combining analyses of data time series, theoretical modelling, and developing methods and protocols for mapping and monitoring coastal bivalve communities.

Insights from a 15-year time series of Pacific oysters in Scandinavia: How are they doing?

Together with Dr Åsa Strand (IVL Swedish Environmental Research Institute) we maintain a time-series of data collected at five locations in Bohuslän, Sweden, where the Pacific oysters have been established since 2006. We analyse this time series to determine how environmental variables such as temperature, salinity, and ice cover, drive fluctuations in biological parameters such as mortality, recruitment, and individual growth. Preliminary analyses show that cold winters such as those in 2009/2010, 2010/2011, and 2020/2021 increase mortality in shallower waters, but oysters established in deeper waters (below 0.7 meters) survive very well and thus maintain the populations. Similarly, the summer-mortality-inducing oyster herpes virus may decimate large proportions of oysters in certain locations, but oysters in other locations remain entirely unaffected.

Tracking the invasion fronts of the Pacific oyster in Northern Europe: Where are they going?

Pacific oysters in Northern Europe are found as far south as Kiel and as far north as Ålesund indicating that individuals are able to survive and settle
in new locations. Further expansion is limited by two main factors; lower salinities in the Baltic Sea and lower temperatures along the Norwegian coast. To track the invasion front and assess the speed of the invasion, we are setting the baseline for the current Pacific oyster distribution in Northern Europe by performing tracking the two invasion fronts; the Norwegian west coast and the coastlines of the western Baltic Sea. In 2021-2022 we will survey coastlines and register presence and absence of Pacific oysters, substrates and depth distribution, population densities and size of individual oysters.

Identifying conflict areas for managing, harvesting, and protecting oysters: Can we conserve the flats and manage the Pacifics?

Using different species distribution modelling tools, we identify areas with high-density of local bivalves such as blue mussels and flat oysters and areas with competitive interaction from Pacific oysters to identify areas where management actions to prevent the Pacific oysters from outcompeting local species are necessary, cost-effective, and feasible. Moreover, we use modelling tools to predict range shift and future trends in competition between the flat oysters and blue mussels. The work is lead by PhD fellow in the Laugen Lab, Molly Reamon, and is a collaboration with Gothenburg University and IVL.

Monitoring Pacific oysters for mud blister worms: Is future commercial harvesting in peril?

The mud blister worm, Polydora websteri,is a shell-boring parasite, inhabiting burrows excavated from their host’s shells. Commonly abundant on calcareous substrates in shallow waters, P. websteri is globally known as a pest on commercially cultivated oysters, including the Pacific oyster. Infested oysters have been associated with unappealing mud blisters inside the shell, effectively reducing the market value of commercially cultured oysters and causing extensive economic losses worldwide. The budding Scandinavian oyster industry that aims at harvesting wild Pacific oysters commercially is — understandably — worried over the recent detection of mud blister worms in Bohuslän (Wrange, Stake, Laugen, et al, in prep). As of May 2021, the mud blister worm appears to be absent in Agder (AT Laugen & PC Hoelfeldt Lund , own observations), but we will be monitoring oysters in Norwegian waters closely over the coming years.