title: Hydrogeomorphic stressing and the response of endangered freshwater pearl mussels, Margaritifera margaritifera: a trait-based approach to inform conservation management
Creators: name: Curley, Edward A.M.
Publisher: name: University of Glasgow
Year: 2021
Subjects: subject: Behaviour, physiology, remote sensing, hydropower, invertebrates, pollution, river.

description: The freshwater pearl mussel, Margaritifera margaritifera, is considered vital to conserving the ecological integrity of freshwater systems, fulfilling the criteria of a keystone, flagship, indicator and umbrella species. Yet populations of this rare, long lived freshwater bivalve have witnessed substantial declines across the species’ Holarctic range. River systems in the Scottish Highlands continue to support large reproductively viable populations; many of which inhabit regulated rivers, managed for hydroelectric energy production. However, there has been limited study concerning the response of M. margaritifera to alterations in habitat characteristics resulting from dam operation. Utilising a combination of field and laboratory experiments, this study aimed to address knowledge gaps regarding interactions between M. margaritifera and the hydrogeomorphological processes occurring within their habitat, providing urgently needed empirical evidence to drive future conservation strategies implemented by government (NatureScot, SEPA) and utilised by the hydroelectric industry (SSE). Initial lab-based work sought to derive methods to non-invasively quantify mussel stress. Here, variation in the expression of particular behavioural metrics was examined in accordance with measurements of oxygen consumption, across environmental stressors, and between two freshwater mussel species. Results from this study revealed an increase in the presence of behavioural traits associated with valve activity in response to stress exposure, in accordance with substantial deviations in metabolic functioning of corresponding individuals. This study corroborates previous work highlighting the potential of bivalve filter feeding organisms as indicator species for alterations in habitat conditions. Furthermore, results exhibit the applicability of these techniques to non-invasively quantify physiological stress in Unionid mussels, towards understanding thresholds in response to environmental stressors across individuals, populations and species. To understand the response of M. margaritifera to alterations in flow regime, resulting from drought conditions and dam operation, flume experiments examined the responses M.margaritifera from two different populations, to three different rates of drawdown, using two different spatial arrangements. Results demonstrated a propensity of M. margaritifera to detect alterations in flow depth, utilising vertical and horizontal movements to avoid prolonged aerial exposure. Data from this study foregrounded intraspecific variation between populations, indicating potential variation in behavioural phenotypic traits. Results from a field trial in a regulated system, using a subset of the corresponding M. margaritifera population, endorsed findings from the flume study. Evidence presented in this study advocates forcontrolled drawdowns in regulated rivers to assist in reducing mortalities associated with receding water levels, during periods of drought. Finally, this study developed and tested novel smart-sensors housed within mussel shells to provide an affordable, accurate and accessible tool to record near-bed flow dynamics in aquatic systems. The resulting instrumented shells were found to accurately detect, and potentially predict entrainment events in M. margaritifera. Entrainment risk was dependent on the flowrate, shell orientation and size; consequently, highlighting the importance of vertical movements in mitigating flow forcing, and the vulnerability of smaller mussels to high flow events. This tool could assist in identifying suitable habitat for M. margaritifera, guiding reintroduction and translocation efforts, and identifying at risk populations to surges in flow discharge. Recommendations are made towards future conservation management of M. margaritifera in Scotland, with a focus on adopting a context-driven approach at the population level. Work in this thesis has provided a foundation for the development of future monitoring techniques to improve understanding of M. margaritifera habitat requirements, in consideration of hydrogeomorphological processes.