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Interactions between freshwater mussels and non-native species

Biological invasions contribute to ecosystem change globally, with a disproportionate and intensified impact in freshwaters. This process is exacerbated in modified systems such as hydrogeneration reservoirs that promote favourable conditions for non-native species proliferation. One of the major threats from non-native species is the introduction of novel interactions that may be particularly impactful on species in affiliate (dependent) relationships and that have narrow habitat requirements during early life-stages. Freshwater mussels (Bivalvia: Unionida) are sessile benthic organisms in affiliate relationships with host fish on which they complete their ectoparasitic life-stage. Attached larvae (glochidia) transform on suitable fish hosts before dropping off as juveniles on surficial sediments. Significant disruption to such interactions may lead to local extinction if affiliate partners are unable to be replaced (i.e., by non-native fish) or the availability of critical life-supporting habitats is reduced (e.g., by non-native macrophytes). Non-native species may play a role in reducing recruitment leading to the adult-skewed mussel population size-structures commonly observed. Accordingly, this thesis contributes knowledge of the interactions between unionid mussels and non-native species in modified freshwater ecosystems, and provides information to assist in species and reservoir management for unionid mussel conservation. The thesis outputs are presented as chapters that have been published in, submitted to, or prepared for scientific journals. A general introduction (Chapter 1) provides context for a global meta-analysis of non-native species and unionid mussel interactions that highlighted non-native fish and macrophytes as potential threats to New Zealand mussels (Chapter 2). Accordingly, a laboratory experiment on three non-native fish (brown bullhead catfish, Ameiurus nebulosus; rudd, Scardinius erythrophthalmus; and goldfish, Carassius auratus) found mussel glochidia were not transformed in ecologically viable numbers compared to a known host fish (Gobiomorphus cotidianus) for a New Zealand unionid (Echyridella menziesii; Chapter 3). This finding suggested that shifts towards fish communities dominated by non-native species have potential to disrupt the obligate glochidial life-stage of unionid mussels. Dense beds of non-native macrophytes (Ceratophyllum demersum and Egeria densa) were found to produce adverse anoxic and hypoxic conditions potentially fatal to mussels in a field survey of Karāpiro, the most downstream in the Waikato River hydrogeneration reservoir chain (Chapter 4). Here, adverse conditions at the sediment-water interface in littoral zones were mediated by reservoir management of water-level and water-flow, and by macrophyte control via herbicide application in the lower-lacustrine section. A subsequent field survey extended the Chapter 4 results to show that effects of non-native macrophytes at the sediment-water interface depended on macrophyte species and overarching hydrology, whereby adult-skewed mussel population size-structures were present in the lower-lacustrine of Karāpiro but not in the upper-riverine section where recruitment was occurring (Chapter 5). The final chapter combined previous findings to show how various hypothetical scenarios of fish and macrophyte invasions could operate separately (non-native fish only) or in combination to disrupt E. menziesii recruitment (Chapter 6). This hypothetical analysis highlighted the importance of considering the threats of both non-native fish and macrophytes, which operate primarily on different stages of the unionid life-cycle, in freshwater mussel conservation and management. Due to the long life-span of unionids, recognition of non-native species impacts contributing to adult-skewed mussel population size-structures may provide an opportunity to restore disrupted mechanisms supporting their recruitment before local extinction occurs. Globalisation and energy demand facilitate continued biotic homogenisation and loss of associated ecosystem services. In this context, the role of management in preventing and mitigating the impacts of biological invasions on sensitive species with affiliate relationships will become increasingly important in freshwater ecosystems in the future.
Type of thesis
Moore, T. P. (2020). Interactions between freshwater mussels and non-native species (Thesis, Doctor of Philosophy (PhD)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/14149
The University of Waikato
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