Seasonal and spatial variations in biomarker baseline levels within Arctic populations of mussels (Mytilus spp.)

Abstract Climate change and pollution resulting from human activities in the Arctic require reliable monitoring systems in sentinel species. Mytilusspp. are used as sentinel speciesall around the world. The use of Mytilusspp. in environmental monitoring requires knowledge about natural variations in pollution biomarkers. Seasonal variations in baselinelevels of biomarkers were studied over a year in the musselsfrom both upper and lower littoral zonesin Rakkfjorden, Norway, as they underwent their annual reproductive cycle. Spatial variations of these biomarker baselinelevels were measured in five musselpopulations within a 60-km radius from Rakkfjorden to investigate universality of the results from the specific population of Rakkfjorden at a regional scale. Seasonal variations in biomarker baselinelevels were revealed and seemed to be related to the reproductive state of the musselsand the tidal zone. The musselsappeared to be more sensitive to oxidative stress during gametogenesisin autumn and winter, when having lower lysosome membrane stability and lower baselinelevels of antioxidant biomarkers. An increase in baselinelevels of these biomarkers was reported during spawning in spring, however, it was not possible to reveal whether these changes were due to spawning, or to a higher metabolic activity in musselsin response to elevated water temperature and food abundance. The differences between the tidal zones were reflected in reduced size of the musselsfrom the upper littoral zone, their late spawning in the season and increased baselinelevels of antioxidant biomarkers during the coldest month, indicating a more challenging environment in the upper littoral zone. The spatial study indicated that the biomarker baseline levels measuredin Rakkfjorden were no different from the levels measuredin the musselsfrom five other sites and thus, are representative for musselson a regional scale.