Habitat degradation and the decline of the threatened mussel Margaritifera margaritifera: influence of turbidity and sedimentation on the mussel and its host

Abstract

Summary1. Habitat degradation is a major reason for species extinctions. For parasite-host interactions, the decline of a parasite may not only be related to the parasite's tolerance to habitat degradation but also indirectly through the host's tolerance to the same disturbance. 2. Our objective was to explore the cause of population declines of the freshwater pearl mussel Margaritifera margaritifera by relating the age distribution, density and growth of the mussels with turbidity, sedimentation rates and density of the mussel's host, trout Salmo trutta, in 26 Swedish streams.3. An analysis of the age structure of nine mussel populations showed that maximum age differed by 60 years, with five populations having low proportions of juvenile mussels. Adult mussel density was higher at sites where juvenile mussels occurred than at sites lacking juvenile mussels. 4. Growth of adult mussels during the past 10 years was lower in the five streams lacking recent recruitment than in the four streams with recent recruitment, indicating that some environmental factor may be negatively impacting these populations. 5. A comparison among 24 populations indicated that turbidity and sedimentation may be responsible for recruitment failure in 58% of the populations. The age of the youngest mussel was positively related to turbidity and sedimentation, and juvenile mussel density was negatively related to turbidity and sedimentation. In contrast, trout density was not related to recruitment of mussels or sedimentation, but was positively related to turbidity in all streams, both with and without recent mussel recruitment. 6. Synthesis and applications. Recruitment failure of M. margaritifera appears to be related to its own vulnerability to turbidity and sedimentation rather than to its host's response to this type of habitat degradation. The results from our study suggest that managers might be able to evaluate the potential viability of mussel populations by measuring stream turbidity. Restoration activities to improve the mussels' environment should focus on reducing fine material transport into streams.

Conservation status of the freshwater pearl mussel Margaritifera margaritifera in Portugal

“…This situation has already been described for many Iberian and other European populations and is the major factor concerning the survival of this species (Álvarez-Claudio et al, 2000;Hastie et al, 2000;Geist, 2010;Österling et al, 2010;Hastie, 2011;Lois et al, 2014). Nevertheless, with the exception of the River Terva, a few juveniles were present.…”

Community structure and decadal changes in macrozoobenthic assemblages in Lake Poyang, the largest freshwater lake in China

“…The dredging-induced changes in high turbidity, substrate instability, and sediment grain size might have affected the survival, recruitment, and growth of unionids. Several studies have revealed that increased turbidity can reduce the foraging activity and growth of mussels (Osterling et al, 2007;Bucci et al, 2008;Österling et al, 2010), in which processes several potential mechanisms may be involved. The fraction of fine sediments, which were more abundant at sand extraction sites, was generally responsible for clogging sediments and resulted in low oxygen and high ammonia conditions (Augspurger et al, 2007).…”

The effect of mussel farming on sediment dynamics in the Wadden Sea : case studies evaluating the local effects of mussel seed fisheries and mussel harvest on turbidity and sedimentation

“…Sedimentation often has a more local nature compared to increases in turbidity (Thomas et al 2001). Both processes are often addressed in studies describing degradation of marine habitats (Henley et al 2000, Kaiser et al 2006, Airoldi & Beck 2007, Österling et al 2010). …”