Massive die-offs of freshwater bivalves as resource pulses

Abstract

-The winter of 2009/2010 was particularly severe in Northern Portugal resulting in higher river flow levels. A study was undertaken to assess the impact of this situation on several populations of freshwater bivalves (e.g., Anodonta anatina, Corbicula fluminea, Margaritifera margaritifera, Potomida littoralis and Unio delphinus) in the catchments of the Rivers Minho, Douro, Taˆmega, Tua and Sabor. Massive die-offs occurred for all species in all rivers, resulting in the removal of great numbers and biomass from the riverbed to the adjacent riverbanks, reaching maximum values of 2280 individuals.m x2 and 10 225 g wet weight.m x2 , respectively. The invasive Asian clam C. fluminea had both highest density and biomass (however, this invasive bivalve is not dominant in several surveyed sites, and some rivers are still not colonized by this species). Results show that the quantitative and qualitative importance of this carrion transfer to the riverbank should be incorporated in future studies on the assessment of ecosystem function, contributing to a better understanding of the role of freshwater bivalves as resource pulses in adjacent terrestrial habitats. Some of the affected species have conservational importance and these extreme climatic events are predicted to increase in the future. These massive die-off events should be incorporated into management plans and selected restoration measures such as rapid relocation of endangered native mussels back to the riverbed can be easily applied to lessen possible impacts.

Conservation status of the freshwater pearl mussel Margaritifera margaritifera in Portugal

“…Indeed, floods and droughts may increase in the future and this situation may be problematic for pearl mussels. Mortalities of M. margaritifera in several Portuguese rivers were described after floods (Sousa et al, 2012) and the same is possible to occur during droughts (Sousa et al, 2008).…”

Biology and conservation of freshwater bivalves: past, present and future perspectives

“…Anyway, recently, Caryn Vaughn and collaborators were able to show in a variety of empirical experiments in mesocosm or natural conditions that Unionida mussels (i) can influence ecosystem processes and functions by modifying the nutrients dynamics that limit primary productivity and dense aggregations of these bivalve species may act as biogeochemical hotspots that influence the standing crops and composition of algal species (Vaughn et al, 2007;Spooner & Vaughn, 2008;Atkinson et al, 2013); (ii) can increase abundances of grazing aquatic insect larvae 2006Spooner et al, 2012) and (iii) can increase the flux of aquatic insect subsidies to terrestrial predators and in this way can link aquatic and adjacent riparian ecosystems (Allen et al, 2012). This last aspect has been also the focus of some studies in Europe that explore the functional importance of massive mortalities of freshwater bivalves during extreme climatic events (droughts and floods) and how the large accumulation of this biomass near the banks may be an important subsidy from aquatic to adjacent terrestrial ecosystems (Sousa et al, 2012;Bódis et al, 2014). Finally, a small number of studies also explored the importance of these species as ecosystem engineers.…”

Impacts of climate change and land-use scenarios on Margaritifera margaritifera, an environmental indicator and endangered species

“…River section River reach Number of mussels Mussel density (mussels·m −2 )* large floods of early 2010 in several Portuguese rivers described great mortalities of M. margaritifera (Sousa et al, 2012). Similarly, in Scottish rivers (e.g.…”

“…In the Iberian Peninsula, the species is already at the southern edge of its distribution and any changes in the temperature may become problematic (Sousa et al, in press). On the other hand, when subject to extreme climatic events, such as large return-period droughts or floods, high mortalities may occur Sousa et al, 2012). Future climatic scenarios for the Mediterranean basin over the next 50-100 years predict an increase in the mean air temperature (between 1-5°C) and extreme events frequency accompanied by a decrease in the annual precipitation (IPCC, 2014).…”