Abstract
Freshwater pearl mussel is a highly threatened species, and many populations are currently on the brink of local extinction. For example, in south Finland, only two populations are currently viable. Even though the reasons for the mussels’ demise are relatively well known, the long-term impacts of water quality are not completely resolved. Here, µ-XRF analysis and historical records were used to evaluate whether the differences in water chemistry or past environmental changes in three rivers in southern Finland are visible in mussel shell chemistry. The results show that the cracks inside mussel shells, invisible to the naked eye, may greatly affect the elemental composition results. Further, anomalies which could be related to inclusion of detrital matter inside the shells were detected. Manganese (Mn) seems to be related to mussel growth dynamics, especially in the nacreous layer, while high values of iron (Fe) and Mn are also present at the top sections of the prismatic layer. Line scan analysis revealed high variation between replicates. The µ-XRF method could be used as prescreening method in mussel sclerochemistry studies, but more studies are needed to clarify the ability of FPM shells to reliably record the environmental conditions.
Highlights
The freshwater pearl mussel, FPM (Margaritifera margaritifera L.), is an endangered bivalve, which has been declining throughout the European part of its range during the past decades [27], and the species is protected within the European Union [10]
River Ruonanjoki shells were clearly thinner than the shells from other studied rivers
The similar condition of mussel shells suggests that the mussels had died at approximately same time [24]
Summary
The freshwater pearl mussel, FPM (Margaritifera margaritifera L.), is an endangered bivalve, which has been declining throughout the European part of its range during the past decades [27], and the species is protected within the European Union [10]. The FPM prefers clear and clean waters, where the bottom substrate is clean gravel material and the reproduction success depends on adequate populations of host fish, in Europe, brown trout and Atlantic salmon [27]. The reasons behind the demise of FPM are related to pearl fishing, which is nowadays illegal in European countries, loss of host fish communities (e.g., due to hydropower dams), decline in water quality (eutrophication, pollution) and siltation (drainage of forest and peat lands, channel manipulation, road construction) [4, 14, 32].
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