Alan Cottingham

Understanding the behavioral strategies that allow freshwater mussels to persist under environmental stress is essential for their conservation, yet burrowing behavior remains poorly quantified. We tested whether valve movement data could be used to detect and characterize burrowing in the endangered Westralunio carteri; a species endemic to a region undergoing severe climatic drying. Mussels from multiple populations were monitored individually under laboratory conditions using Hall effect sensors, and valve movement patterns were analyzed to distinguish between burrowing and non-burrowing behaviors. Burrowing was associated with rapid, high-amplitude valve movements that lengthened as burial progressed, while non-burrowing behaviors showed distinct, slower patterns. These differences indicate that valvometry can reliably identify burrowing behavior, providing a non-invasive method for monitoring mussel activity. This approach has broad applications for ecological research, conservation assessment, and early-warning biomonitoring of imperiled freshwater mussel populations.

Coastal environments and their associated biota provide numerous environmental, economic and societal services. Cockburn Sound, a temperate embayment on the lower west coast of Western Australia, is immensely important for the State and adjacent capital city of Perth. However, urbanisation and associated terrestrial and marine development has the potential to threaten this important ecosystem. This study collated published and unpublished data to review the current state of the ecological resources of Cockburn Sound and describe how they have changed over the past century. Post-WWII, the embayment began undergoing pronounced anthropogenic changes that limited oceanic water exchange, increased nutrient load, modified benthic habitats and increased fishing pressure. The most visual outcome of these changes was substantial eutrophication and the loss of 77% of seagrass habitats. However, the increased primary productivity from elevated nutrient inputs produced high commercial fishery yields of up to ~1,700 t in the early 1990s before improved wastewater regulation and restricted fishing access steadily reduced commercial catches to ~300 t in recent years. Despite substantial anthropogenic-induced changes, Cockburn Sound has remained a diverse and ecologically important area. For example, the embayment is a key spawning area for large aggregations of Snapper, is a breeding and feeding site for seventeen marine bird species (including Little Penguins) and, is frequented by numerous protected species such as pinnipeds, dolphins, and White and Grey Nurse sharks. In recent decades, numerous projects have been initiated to restore parts of Cockburn Sound with mixed success, including seagrass transplantation, deployment of artificial reefs and stocking of key fish species, mainly Snapper. Nevertheless, while still biodiverse, there are signs of considerable ecological stress from escalating anthropogenic pressures and the cumulative impacts of ongoing and future developments, including climate change, which may severely impact the functioning of this important ecosystem.

This report describes the monitoring and evaluation of fish communities in the Bindjareb Djilba (Peel-Harvey Estuary), Waangaamaap Bilya (Serpentine River) and Bilya Maadjit (Murray River) during the summer and autumn of 2023 using the Fish Community Index (FCI), which was developed as a measure of the ecological condition. This index, which was specially designed to work in south-western Australian estuaries, has versions developed for both the shallow, nearshore waters of the estuary (≤ 1 m deep) and also for its deeper, offshore waters (> 1 m deep) using an extensive fish data set from the 1970s to 2018. The index integrates information on various biological variables (metrics). Each of these metrics quantifies an aspect of the structure and/or function of estuarine fish communities, and together, they respond to a range of stressors affecting the ecosystem.

Fish communities were sampled using different nets at six nearshore and four offshore sites in eight and seven regions of the Peel-Harvey Estuary, respectively (MC, Mandurah Channel (nearshore only); EP, Eastern Peel; WP, Western Peel; NH, Northern Harvey; SH, Southern Harvey; SP, Serpentine River; LM, Lower Murray River and UM, Upper Murray River) during summer and autumn of 2023. As many fish as possible were returned to the water alive after they had been identified and counted. The resulting data on the abundances of each fish species from each sample were used to calculate a Fish Community Index score (0 – 100). These index scores were then compared to established scoring thresholds to determine ecological condition grades A (very good) to E (very poor) for each region and the estuary as a whole, based on the composition of the fish community. This method has been adopted annually for over a decade in Derbal Yirragan Djarlgarro (Swan-Canning Estuary) and has been shown to be a sensitive and robust tool for quantifying ecological health responses to local-scale environmental perturbations and tracking the subsequent recovery.

The WAMSI Westport Marine Science Program (WWMSP) is a $13.5 million body of marine research funded by the WA Government. The aims of the WWMSP are to increase knowledge of Cockburn Sound in areas that will inform the environmental impact assessment of the proposed Westport development and help to manage this important and heavily used marine area into the future. Westport is the State Government’s program to move container trade from Fremantle to Kwinana, and includes a new container port and associated freight, road and rail, and logistics. The WWMSP comprises more than 30 research projects in the biological, physical and social sciences that are focused on the Cockburn Sound area. They are being delivered by more than 100 scientists from the WAMSI partnership and other organisations.

Various types of tidal barriers are used in estuaries to reduce saltwater intrusion and regulate freshwater discharge, but they often alter the physicochemical environment and faunal composition. With the use of these structures expected to increase due to climate change, there is a need to understand their impacts. A tidal exclusion barrier in the Ramsar-listed Vasse–Wonnerup Estuary (Australia) was found to act as an ecotone, fragmenting the estuarine gradient into two distinct components, a relatively stable marine-like environment downstream and a highly variable oligohaline to hypersaline (~0 to >100 ppt) environment upstream. The downstream regions contained a speciose and functionally rich estuarine fauna, comprising mainly polychaetes and bivalves. The upstream regions were taxonomically and functionally depauperate, containing insects, gastropods, and ostracods typically found in saline wetlands. The fragmentation of the estuary has likely impacted the provision of ecosystem services, with the fauna downstream mainly comprising burrowing species that bioturbate and, thus, aid in nutrient cycling. In contrast, the environmental conditions caused by the barrier and the resultant epifaunal invertebrate assemblages upstream aid little in bioturbation, but provide nutrition for avian fauna. These results may help in understanding the impacts of constructing new barriers in coastal ecosystems in response to climate change.

Shellfish reefs were once common features in temperate coastal waters and estuaries. However, anthropogenic impacts have resulted in significant declines in these ecosystems globally. Whilst a growing body of scientific literature and restoration projects have demonstrated the success of restoration using oysters, at both local and ecosystem-wide scales, restoration initiatives using mussels are relatively new. Due to the lack of long-term data on the ecological impact of restored mussel reefs, information to assist restoration practitioners in identifying potential positive and negative outcomes is limited. However, introductions of mussels have occurred on every continent, and detailed documentation exists on their impacts on local ecosystems. Such information is thus invaluable as these long-term studies can contribute knowledge on predicting ecosystem changes following mussel introductions. Through compiling information derived from 318 published articles, unplanned mussel introductions were found to have both positive and negative impacts, and these were context- and species-specific. In eutrophic water bodies, the impacts were typically considered positive, particularly on shallow-water benthic communities. It was also found, however, that mussels can reduce zooplankton biomass, impact native mussels and were occasionally implicated in increasing cyanobacteria concentrations. Despite these instances, this review presented multiple lines of evidence that mussel introductions, when undertaken intentionally at suitable locations, would have a considerable positive impact at the ecosystem-wide scale.

Through altered freshwater flow regimes and excessive anthropogenic nutrient input, many estuaries around the world are showing signs of eutrophication. As shellfish can alleviate some of these issues through their water filtration capacity, shellfish habitat restoration efforts have increased markedly in the past decade. This study quantifies, for the first time, the water filtration capacity of the Black Pygmy Mussel Xenostrobus securis and the potential for habitat enhancement to alleviate eutrophication issues in a hypereutrophic estuary in south Western Australia. Substrate, comprising coir matting, was deployed by community volunteers in four‐panel arrangements in the rivers of the Swan‐Canning Estuary onto which X. securis recruited naturally. In the Swan River, average mussel densities were 3377 individuals m −2 , based on 10% mat coverage. River water comprised relatively high particulate organic matter (POM) concentrations, particularly in spring (up to 9.2 mg L −1 ). Standardised clearance rates (CR; g −1 mussel tissue) were typically greater (> 5.0 L h −1 ) in summer when chlorophyll a concentrations, salinities and water temperature were elevated, whereas CR was often < 2.0 L h −1 in early spring. In the Swan River, it was estimated that for every square metre of habitat enhanced, 9.2 × 10 5 L of water could be potentially cleared during spring and 1.7 × 10 6 L over summer, the latter incorporating 5.3 kg of organic matter into mussel biomass. On a larger scale, 1000 m 2 of deployed habitat over the course of summer has the potential to clear 24.5% of the volume of the tidal portion of the Swan River and 64.4% of the volume of the smaller Canning River. The results thus demonstrate the efficacy of using cost‐effective soft substrates deployed by community volunteers to enhance habitat for mussels and its potential to assist in alleviating eutrophication issues.

Tidal-exclusion barriers have routinely been constructed within estuaries throughout the world to moderate the risk of flooding by marine incursions. These barriers have been shown to impact ecological connectivity, however, their impact on the movement patterns of obligate estuarine fishes is poorly understood. We aimed to determine the environmental drivers of movements through a fish passage gate within a tidal exclusion barrier by the temperate sparid Black Bream (Acanthopagrus butcheri), which occasionally suffers from large-scale mortality events that predominantly occur in the adjacent habitat upstream of the barrier. Fish were fitted with passive integrated transponder (PIT) tags and their fine-scale passage was recorded using a monitoring system that acted as a gate at either end of the barrier over 14 months. Hydrological and environmental predictor variables were included in generalised additive mixed models to determine the drivers of upstream and downstream passages through the gate on an hourly and daily basis. Successful upstream and downstream passages were associated with times of minimal flow velocity within the fish gate that occurred when water levels equalised on both sides of the barrier. Downstream passages were also associated with declines in dissolved oxygen concentrations upstream of the barrier; suggesting that fish were seeking to escape poor water quality. However, as passage opportunities to avoid unfavourable conditions were influenced by tides that equalised the water levels, periodic mass fish mortality events can occur upstream of the barrier. As climate change will increase saltwater incursion and storm-related flooding risks, there will be a greater need for tidal exclusion barriers in many regions. This study underscores the need to understand the movement patterns of fishes in estuaries to maintain the connectivity of populations.
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•Tidal-exclusion barriers can deleteriously impact ecological connectivity.•Movements of an estuarine-resident sparid fish through a fish passage gate investigated.•Passages occurred at times of minimal flow velocity within the fish gate.•Passage opportunities to avoid poor water quality limited by tides.

Estuaries that become closed from the ocean through the formation of a sand bar are particularly susceptible to degradation and often experience poor water quality and fish kills. Sampling was conducted seasonally for two years in the deeper waters of the Vasse–Wonnerup (southwestern Australia) after a large fish mortality event to identify the fish species present and determine if richness, abundance, diversity and faunal composition differed among regions and over time. Species richness, abundance and diversity were far greater in the downstream regions than in the upstream regions, reflecting patterns in salinity. Catch rates of two marine estuarine-opportunist mugilids (Mugil cephalus and Aldrichetta forsteri) and an estuarine-resident sparid (Acanthopagrus butcheri), which were the species most affected by the mortality event, were relatively stable. It is suggested that before sampling commenced, mugilids had entered the estuary following an artificial sand bar breach, while the loss of 0+ (new recruits) A. butcheri in the mortality event and subsequent recruitment failure prevented stocks from increasing. Temporal shifts in fish composition were driven by less abundant species, which utilized the estuary more opportunistically. Increases in the occurrences and abundances of these species coincided with an open bar and salinities close to those of seawater. The data also show how the estuary responds to differing hydrodynamic phases and artificial breaches.

Shellfish reefs around the world have become degraded, and recent efforts have focused on restoring these valuable habitats. This study is the first to assess the efficacy of a bouchot-style reef, where mussels were seeded onto wooden stakes and deployed in a hypereutrophic estuary in Australia. While >60% of translocated mussels survived one month, after ten months, only 2% remained alive, with this mortality being accompanied, at least initially, by declining body condition. Mussel survival, growth, body condition and recruitment were greater on the top section of the stake, implying that the distance from the substrate was important. More fish species inhabited the reefs (31) than unstructured control sites (17). Reefs were also colonised by a range of invertebrate species, including 11 native and six non-indigenous species. However, the number of individuals declined from 4495 individuals from 14 species in December 2019 to 35 individuals representing 4 species in March 2021, likely due to hypoxic bottom water conditions following unseasonal rainfall. Although the bouchot-style reefs were unable to sustain mussels and other invertebrates over sequential years, this approach has the potential to be successful if deployed in shallow water or intertidal zones, which are largely exempt from biotic and abiotic stressors characteristic of deeper waters in microtidal estuaries.