Behaviour and physiology are linked in the responses of freshwater mussels to drought

Abstract

Summary 1. Droughts have become prevalent in the south‐eastern U.S.A. and are predicted to become more common in the future. Drought conditions have particularly strong negative effects on sessile aquatic organisms with limited dispersal ability. This study explored the linkages between physiological tolerance, behavioural response and survival of three species of freshwater mussels subjected to drought. 2. To assess physiological tolerance, we measured survival under desiccation at 25, 35 and 45 °C in the laboratory. To assess behavioural responses, we tracked horizontal and vertical movement of mussels in a drying stream reach. 3. Uniomerus tetralasmus showed the greatest desiccation tolerance, Lampsilis straminea was intermediate, and Pyganodon grandis had the lowest tolerance at all temperatures. 4. In the drying stream reach, U. tetralasmus showed little horizontal movement and quickly became stranded. The other two species tracked the receding water. It was not until the pool had been reduced to c. 10% of its original size that ≥50% of P. grandis and L. straminea became stranded. 5. Uniomerus tetralasmus and L. straminea burrowed in response to becoming stranded; however, both species burrowed only shallowly (3–4 cm), presumably because burrowing to greater depths did not convey increasing thermal refuge. Pyganodon grandis rarely burrowed. No P. grandis survived the 15‐week drought, while 45% of L. straminea and 77% of U. tetralasmus survived. 6. Three strategies emerged for freshwater mussels to cope with drought conditions: tracking (intolerant), track then burrow (semi‐tolerant) and burrowing (tolerant). Results suggest that drought poses the greatest threat to intolerant trackers, while tolerant burrowers are the most resistant to drought conditions.

Effect of substratum drying on the survival and migrations of a freshwater pulmonate snail Planorbarius corneus (Linnaeus, 1758)

“…The ability to survive prolonged desiccation and drought depends not only on physiological tolerance, as shown above, but also on behavioural strategies (Gough et al, 2012). In our experiments, P. corneus demonstrated distinct horizontal migrations following the changing water level.…”

“…In our experiments P. corneus burrowed just below the substratum surface, similarly to some other gastropods (Duft et al, 2003) and bivalves (Gough et al, 2012), whereas other pulmonate species from temporary ponds bury to depths as great as 7 cm (McMahon, 1983after Cheatum, 1934. Survival time during drought may be increased in the field, if snails can find relatively humid, protected microhabitats in the sediments (Machin, 1975;Facon et al, 2004;Collas et al, 2014).…”

“…Survival time during drought may be increased in the field, if snails can find relatively humid, protected microhabitats in the sediments (Machin, 1975;Facon et al, 2004;Collas et al, 2014). Shallow burrowing in moist substratum to decrease temperature is a very efficient strategy to survive desiccation, particularly if a species exhibits additional physiological adaptations to live inside sediments (Gough et al, 2012). Buried snails decrease activity and switch to purely cutaneous breathing or anaerobic metabolism (Machin, 1975;McMahon, 1983), which makes them highly tolerant to anoxia.…”

“…Gough et al, 2012;Kapps & Haase, 2012). In some cases burying behaviour precedes aestivation (Machin, 1975).…”

A Tale of Two Rivers: Implications of Water Management Practices for Mussel Biodiversity Outcomes During Droughts

“…The influence of stream flows on mussels is pervasive, making them a model study system to investigate the environmental effects of hydrological alterations. Mussels rely on predictable stream flows for reproduction (Galbraith and Vaughn 2011), the maintenance of tolerable temperatures (Gagnon et al 2004;Spooner and Vaughn 2008;Gough et al 2012) and stable habitats (Allen and Vaughn 2010), as well as the abundance of host fish required for juvenile mussel recruitment (Roy et al 2005;Vaughn 2012). Changes in hydrology due to dam construction and river channelization is considered to be the primary cause of mussel declines in the US (Vaughn and Taylor 1999;Strayer et al 2004), and effects of climate change and water withdrawals are predicted to accelerate mussel declines in the future (Spooner et al 2011).…”