Connectivity plays an important role in shaping the genetic structure and in evolution of local adaptation. In the marine environment barriers to gene flow are in most cases caused by gradients in environmental factors, ocean circulation and/or larval behavior. Despite the long pelagic larval stages, with high potential for dispersal many marine organisms have been shown to have a fine scale genetic structuring. In this study, by using a combination of high-resolution genetic markers, species hybridization data and biophysical modeling we can present a comprehensive picture of the evolutionary landscape for a keystone species in the Baltic Sea, the blue mussel. We identified distinct genetic differentiation between the West Coast, Baltic Proper and Bothnian Sea regions, with lower gene diversity in the Bothnian Sea. Oceanographic connectivity together with salinity and to some extent species identity provides explanations for the genetic differentiation between the West Coast and the Baltic Sea (Baltic Proper and Bothnian Sea). The genetic differentiation between the Baltic Proper and Bothnian Sea cannot be directly explained by oceanographic connectivity, species identity or salinity, while the lower connectivity to the Bothnian Sea may explain the lower gene diversity. © 2016.

Human-derived environmental pollutants and nutrients that reach the aquatic environment through sewage effluents, agricultural and industrial processes are constantly contributing to environmental changes that serve as drivers for adaptive responses and evolutionary changes in many taxa. In this study, we examined how two types of point sources of aquatic environmental pollution, harbors and sewage treatment plants, affect gene diversity and genetic differentiation in the blue mussel in the Baltic Sea area and off the Swedish west coast (Skagerrak). Reference sites (REF) were geographically paired with sites from sewage treatments plant (STP) and harbors (HAR) with a nested sampling scheme, and genetic differentiation was evaluated using a high-resolution marker amplified fragment length polymorphism (AFLP). This study showed that genetic composition in the Baltic Sea blue mussel was associated with exposure to sewage treatment plant effluents. In addition, mussel populations from harbors were genetically divergent, in contrast to the sewage treatment plant populations, suggesting that there is an effect of pollution from harbors but that the direction is divergent and site specific, while the pollution effect from sewage treatment plants on the genetic composition of blue mussel populations acts in the same direction in the investigated sites.

Anthropogenic pollution including metals, petroleum, toxins, nutrients and many others is a growing problem in the marine environment. These are important factors altering the environment and by that the fate of many local populations of marine organisms. The aim of this study was to assess the impact of selected point pollution sources on resident populations of the blue mussel (Mytilus edulis trossulus) in the Baltic Sea using multiple biomarker approach. The study used a nested sampling scheme in which sites from reference (REF) habitats are geographically paired with selected sites from sewage treatment plants (STP) and harbors (HAR). The results showed that mussels from harbors had a higher frequency of histological abnormalities in the digestive gland compared to mussels from sewage effluent affected areas and reference sites. However these mussels together with mussels from STPs had higher lipid content, body mass index (BMI) and gonado-somatic index (GSI) compared to mussels from reference sites. A marked spatial variability was found with a stronger toxicity of ambient environment affecting resident mussel populations in the Gulf of Gdańsk area, while an opposite pattern was found in Tvärminne area. Yet the blue mussels sampled in the Gulf of Gdańsk were characterized by the highest GSI and BMI values compared to Askö and Tvärminne populations. No differences in analyzed biomarker response related to species identity, measured by a species-specific genetic marker, were found indicative of strong genetic introgression in the Baltic Proper.