The ‘canary of the estuary’, the contribution of Sydney rock oyster aquaculture to understanding and protecting Australian estuarine health
Michael C. Dove A , Laura M. Parker A B * , Anthony Zammit C , Hazel Farrell C , Penelope Ajani D , Shauna Murray D , Kirsten Benkendorff
E , Geoff R. MacFarlane F and Wayne A. O’Connor A F *
A
B
C
D
E
F
Handling Editor: Bridie Allan
Abstract
The Sydney rock oyster (Saccostrea glomerata) is an iconic Australian native species of great commercial and ecological significance, that has been farmed in New South Wales for over 150 years.
To highlight the role of S. glomerata industry in safeguarding Australia’s estuaries.
Literature review.
S. glomerata, more than any other species, has served to highlight emerging threats to estuaries, ranging from viral and bacterial contamination to chemical pollution, and climate change. Their use as biomonitors and in bioassays for pollutants (metals, PAHs, PFAS and pesticides) has been instrumental in identifying and quantifying potential threats. The oyster industry provides one of NSW’s largest and longest-running monitoring programs for estuarine environmental conditions. Currently, S. glomerata is at the forefront of remediation efforts, leading legislative change in environmental protection, and using ecoengineering, reef restoration and selective breeding programs to bolster oyster resilience.
Even though the community has long recognised the intrinsic link between oyster health and estuarine well-being and works with industry to advocate for estuarine ecosystem conservation and the species present, the contribution the industry makes is underestimated.
Amid debate over aquaculture expansion, greater consideration of the positives arising from culture activities is warranted.
Keywords: aquaculture, bioassay, climate change, estuarine health, monitoring, oyster, pollution, Saccostrea glomerata.
Introduction
The Sydney rock oyster (Saccostrea glomerata, formerly S. commercialis), holds a significant place as an iconic native oyster species along Australia’s southern coastline, stretching from southern Queensland to Albany in Western Australia (Snow et al. 2023). Historically, this once-abundant oyster served as a valuable food source for Aboriginal communities, before being used for sustenance and lime production during the colonial period in New South Wales (NSW). Its cultivation began in the 1880s, laying the foundation for one of Australia’s oldest aquaculture industries. Most S. glomerata culture occurs in NSW estuaries, although oyster farms are also established in Queensland, Victoria and Western Australia (O’Connor and Dove 2009). Unfortunately, although the industry grows, wild S. glomerata populations have declined by more than 90% (Gillies et al. 2018; McAfee et al. 2020), largely through overharvest, prompting efforts for reef-building interventions.
NSW is Australia’s most populous state, with over 85% of its population residing within 50 km of the coast, being primarily concentrated around estuarine areas (Planning NSW 2023). Consequently, the S. glomerata industry has evolved alongside significant anthropogenic impact, with sites such as Sydney Harbour once considered among the world’s most contaminated environments (Davis and Birch 2010, 2011). Given the economic and ecological significance of S. glomerata and its ability to accumulate pollutants, there has been extensive research into various anthropogenic threats (Avery et al. 1996: Ewere et al. 2019a, 2019b: Islam et al. 2024). Oysters are often called the ‘lungs of the estuaries’ or ‘canaries of the estuary’, with their health serving as an indicator of river health issues (Healthy Rivers Commission 2003). They are well suited as biomonitors, because most oysters (including S. glomerata) are broadcast spawners and their embryonic and larval stages are exposed to general environmental conditions. Both the larvae and adult stages are exposed to high volumes of seawater in proportion to their size, with adult S. glomerata capable of filtering over 100 L day−1 (7.2 L day−1 g−1 of oyster; Bayne 2002).
Initially, concerns over pollutant threats to S. glomerata focused on bacterial contamination and metals, including tributyltin (Batley et al. 1989). However, studies have since expanded to encompass the impacts of polycyclic aromatic hydrocarbons (PAHs), endocrine-disrupting chemicals (EDCs), and emerging threats such as pesticides, perfluoroalkyl substances (PFAS) and microplastics. S. glomerata has also played a crucial role in assessing key threatening processes such as climate-change-induced ocean warming and acidification, with this research contributing to the resilience of industry production and supporting reef restoration initiatives (Pereira et al. 2020).
Beyond its role as a beloved seafood staple contributing to NSW’s most valuable fishery (valued at A$77 million in 2022–23, NSW Department of Primary Industries and Regional Development 2024), S. glomerata has been instrumental in driving environmental protection efforts for NSW’s estuarine environments. In the Sydney Morning Herald, Lockwood (2014) reported that
Oysters are the canaries in the mine or marine world, and less oysters mean less fish. But they are just the tip of the iceberg when it comes to pollution woes and researchers fear other marine critters are under great stress.
Concerns for Sydney rock oyster health have spurred legislative changes since the 1870s, and, thanks to a proactive industry, continue today. Larval S. glomerata have been used widely in bioassays to assess the impacts of pollutants, and adults have been used as biomonitors for diffuse and point-source pollution events (Avery et al. 1996; Scanes 1996; van Dam et al. 2008). Monitoring S. glomerata in estuarine environments has uncovered emerging pollution problems (Jamal et al. 2024), and when new problems are discovered, they were among the first species tested to assess biological impacts. While other estuarine species such as mangroves and seagrasses have been focal points of protection efforts, few have been as influential in advocating for NSW estuary preservation as S. glomerata. This review is not an attempt to chronicle the myriad studies of anthropogenic impacts on S. glomerata, rather it seeks to highlight the sometimes-undervalued role that cultured species can have in protecting the environments they rely on.
History
For at least 10,000 years, oysters and other foods harvested from Australian estuaries have served as vital sources of sustenance and nutrition for Aboriginal communities (Gibbs et al. 2024). From the earliest European observations, the richness of NSW estuarine resources was recognised and prized. Early settlers relied on these resources for food, and in the case of oysters, as a source of lime for construction. Consequently, there exists a longstanding tradition of valuing our estuarine ecosystems and making efforts to safeguard them.
During colonial Australia, Royal Commissions emerged as powerful instruments to investigate public issues, often preceding legislative reform (Gilligan 2002). One of the earliest Royal Commissions convened in NSW (1865–1866) focused on an ‘Inquiry into the Condition of the Harbour of Port Jackson’ (Sydney, NSW), which included an examination of the impacts of city sewage on the harbour environment. This concern for the estuarine environment, particularly for S. glomerata, resurfaced little more than a decade later in 1876 when the Royal Commission on Oyster Culture was established to explore methods for maintaining the colony’s natural oyster beds. Subsequently, in 1884, an Act of Parliament was made for the preservation and cultivation of oysters, laying the groundwork to develop the oyster industry as we know it today. Areas within estuaries were leased to farmers for the cultivation of oysters, which were to become the sole source of oysters for commercial exploitation, preventing large-scale natural oyster harvest. Since then, oysters have played a pivotal role in identifying and raising awareness of various threats to the health of our estuaries, serving as indicators of the efficacy of conservation efforts (Fig. 1).
Celebrating the return of oysters to Sydney Harbour, front page, Sydney Morning Herald on 25 January 2002 (Morris 2002), at the time, one of the highest-circulation papers in Australia’s largest city.
The threat posed to S. glomerata, particularly its safety as a food product, was a regular source of concern to Sydney’s residents and was frequently discussed in newspapers. Following the 1856 Royal Commission, sewage pollution of Sydney Harbour, and later Botany Bay, remained topical for well over a century. The closure of Middle Harbour (in Sydney Harbour) to oyster harvest in the early 1900s led to headlines such as ‘Poison in the local oysters. A remarkable revelation’ (Anon. 1903) and charges being laid for illegal oyster collection (Anon. 1906).
As Sydney developed, new sources of pollution were recognised. Proposals to build an oil refinery in Botany Bay in the late 1930s raised new fears. Mr T. C. Roughley, Special Research Officer of the Fisheries Department, warned ‘that if effluent from such works reached Botany Bay it would be of great detriment to oyster farms’, and went on to say, ‘We have been too complacent in the past about pollution of our bays and rivers’ (Anon. 1940).
In 1995, the NSW Government established the Healthy Rivers Commission to conduct independent public inquiries into selected NSW rivers and propose long-term strategies to achieve environmental, social and economic goals. These inquiries included major oyster-producing estuaries, such as Georges River, Hawkesbury River and Shoalhaven River. Oysters were so topical, that the NSW Government subsequently requested that the Healthy Rivers Commission specifically examine the relationship between river health and the cultivation of oysters safe for human consumption. The widespread recognition of the correlation between healthy estuaries and safe oysters has led to continued legislative support for the NSW oyster industry. In 2006, the Oyster Industry Sustainable Aquaculture Strategy (OISAS) was publicly announced, along with amendments to NSW State Environmental Planning Policy 62 – Sustainable Aquaculture (State Environmental Planning Policy, SEPP 62). OISAS identified Priority Oyster Aquaculture Areas (POAAs) in each estuary, established water quality objectives for these areas based on Healthy Rivers Commission recommendations (Healthy Rivers Commission 2003), and placed obligations on oyster farmers for improved farming practices. Subsequent legislation, including SEPP Primary Production and Rural Development 2019 and the current SEPP Primary Production 2021, require consent authorities considering development applications affecting POAA or other oyster aquaculture areas to follow specific procedures, including notifying the Secretary of the Department of Industry, considering OISAS provisions, and evaluating any proposed measures to address compatibility issues with oyster aquaculture.
Whether addressing the historical threat of sewage pollution in Port Jackson nearly 170 years ago or confronting the myriad pollutants of the Anthropocene era, S. glomerata has consistently played a pivotal role in detecting, highlighting and addressing environmental threats.
Environmental change
Physical environmental variables
Marine environments are highly susceptible to fluctuations in salinity and temperature, and these are among the first variables considered in attempting to understand the biology and ecology of estuarine species. The NSW oyster industry has been a source of these data since the mid-1960s (Wolf and Collins 1979) and continues to support investigative programs. As part of the comprehensive commercial shellfish program monitoring in NSW, salinity and temperature measurements are systematically collected alongside microbiological, phytoplankton and biotoxin samples. This results in the acquisition of up to 20,000 environmental data points annually. With the increasing availability of real-time monitoring sensors, recent initiatives, such as the projects spanning from 2017 to 2021 and from 2021 to 2024 (Murray et al. 2024), have enhanced baseline monitoring in major oyster-producing estuaries (Ajani et al. 2024). These projects have intensified sampling intervals to 15–30 min for temperature and salinity, with all data being publicly accessible and utilised across a diverse array of estuarine investigations (see https://salinity.research.uts.edu.au). In some estuaries, extensive sensor arrays have been installed and have been coupled to terrestrial weather stations to enhance the data provided and the range of applications (Bates et al. 2021; Hornsby Shire Council, see https://mhl.nsw.gov.au/users/HornsbyShireCouncil/). Without the oyster industry, the quantity, duration and availability of foundational environmental data to support estuarine research would be significantly reduced. Particularly, in the face of climate change, where 50 years of data will likely be of great value.
Algal toxins
Phytoplankton play a crucial role at the foundation of most marine food chains and serve as a primary food source for oysters; however, some naturally occurring phytoplankton produce toxins with potentially severe impacts on the wider marine ecosystem and seafood consumers. Because these toxins can accumulate to levels toxic for humans relatively quickly (days to weeks, Farrell et al. 2015), there is a regulatory requirement for monitoring in shellfish safety guidelines (i.e. Australian Shellfish Quality Assurance Advisory Committee 2024). Because of its size, the majority of marine phytoplankton and algal toxin monitoring on Australia’s eastern coast is undertaken by the S. glomerata aquaculture industry. This comprehensive effort involves up to 3000 tests year−1 that are co-funded and collected by the S. glomerata industry. Although the primary objective of this monitoring is to safeguard consumers and ensure human health from algal biotoxins, it also provides valuable insights into estuary health and the impacts of changing climate conditions.
The data gathered from monitoring S. glomerata have led to the detection of new potentially harmful algal species and highlighted recent changes in their frequency of occurrence and the intensity of blooms. The first observations of toxic Pseudo-nitzschia delicatissima blooms in the southern hemisphere were from oyster-growing areas in the Hawkesbury River (Ajani et al. 2020), whereas data from the same area were used to provide the first insights into the dynamics of toxic Dinophysis acuminata blooms in Australia and elucidate the potential mechanism(s) for bloom development (Ajani et al. 2016).
Comprehensive datasets of harmful algal blooms in Australian waters are rare (Ajani et al. 2017), with the largest and longest-running dataset arising from testing in S. glomerata. Here alone, a total of 54 amnesic shellfish toxin (AST) detections (max. 20 in 2013), 27 diarrhetic shellfish toxin detections (max. 11 in 2013) and 102 paralytic shellfish toxin detections (max. 30 in 2010) were recorded from 2004 to 2015 (Ajani et al. 2017). At that time, all but one of these events, an AST detection (20 samples) in Wagonga Inlet in 2010, remained below the regulatory limit and posed little threat. Since 2016, more frequent and larger-scale blooms of Alexandrium pacificum causing toxins above the safe limit for human consumption appear to be occurring (Barua et al. 2020) with the highest recorded levels of paralytic shellfish toxins in S. glomerata observed during late 2022. This event also affected other seafood species and prompted the government to advise all recreational seafood consumers of the potential threat (NSW Department of Primary Industries and Regional Development 2022).
The importance of rapid and sensitive detection of toxins in S. glomerata has been the impetus for the development of new detection methods. For example, the detection of a bloom of mixed Pseudo-nitzschia species in oyster leases at Wagonga Inlet, NSW, led to the development of a quantitative real-time polymerase chain-reaction (qPCR) assay to detect only species belonging to the toxin-producing P. pseudodelicatissima complex. The data from this assay were then used alongside high-resolution water temperature and salinity sensor data from oyster leases to develop predictive models of the abundance of P. delicatissima within the estuary to warn of future blooms (Ajani et al. 2021).
Ocean acidification and warming
Climate change poses a significant threat, with the potential to severely disrupt and alter marine and estuarine environments worldwide. Human activities have led to an increase in the concentration of carbon dioxide (CO2) in the atmosphere, causing estuaries and oceans to undergo acidification and warming at an unprecedented rate on geological timescales. This trend is projected to persist throughout this century (Collins et al. 2013; Lee et al. 2021). In Australia, these changes are already observable in estuarine environments. Data collected from 166 estuaries along the Australian coastline showed significant warming and acidification, in particular, with the eastern Australian estuaries, which are a home to the largest S. glomerata populations, warming, acidifying and freshening more quickly than predicted by global models (Scanes et al. 2020).
For nearly two decades, the concern has centred on the potential impacts of these changes on marine and estuarine organisms and the ecosystem services they provide. S. glomerata was among the first species globally to be assessed for the impacts of ocean acidification and warming (Parker et al. 2009, 2010; Watson et al. 2009) and has been at the forefront of marine climate-change research since then. Early studies focussed predominantly on early-life history stages and showed detrimental impacts on larval growth and development, the percentage of abnormal larvae, and larval survival. Further studies found that like many other calcifying marine and estuarine species, S. glomerata is vulnerable across each stage in its life cycle, with reductions in juvenile and adult shell growth (Parker et al. 2010; Scanes et al. 2017; Fitzer et al. 2018, 2019) and reproductive capacity (Parker et al. 2018), changes in physiology (e.g. acid–base balance, clearance rate and metabolism; Parker et al. 2012, 2024; Stapp et al. 2018) and alterations in their microbiome (Scanes et al. 2021, 2023). This research has highlighted how pervasive the impacts can be, how varied the mechanisms are, and provided an impetus for similar research in other local molluscan species (e.g. Scanes et al. 2014; Cole et al. 2016; Pereira et al. 2020).
Owing to the severity of climate-change impacts, research on S. glomerata quickly shifted to estimating the capacity for acclimation or adaptation (Parker et al. 2011, 2012, 2015). Parker et al. (2011) demonstrated that genetically distinct pair-mated families of S. glomerata differed in their growth response to ocean acidification, with growth being unaffected in some families. This provided the first evidence that tolerant genotypes may exist within populations of S. glomerata, potentially facilitating genetic adaptation. Following this, it was found that wild populations of S. glomerata can rapidly acclimate to ocean acidification, by a process known as transgenerational plasticity (TGP), which has since been demonstrated in oysters for other stressors such as injections of the immunostimulant poly(I:C) and low salinity (Green et al. 2016; Griffiths et al. 2021). Exposure of adult S. glomerata to ocean acidification during reproductive conditioning in a hatchery setting resulted in positive TGP effects being passed to their offspring. These effects primed the offspring for acidified conditions, enabling them to grow and develop faster with fewer abnormalities than do the offspring from non-exposed parents (Parker et al. 2012). More recently, it was found that adult S. glomerata exhibited considerable resilience to simulated moderate marine heat waves and elevated temperatures (Ewere et al. 2021a). Although some minor changes were observed in the micronutrient and elemental composition of the flesh, there were no significant changes in parameters such as haemocyte numbers, condition index, gene expression, flesh protein, or fatty acid profiles relative to ambient controls. Collectively, these studies have played an important role in shifting the focus of global marine and estuarine climate-change research from solely assessing impacts to considering the capacity for resilience, acclimation and adaptation.
In 2020, Oysters Australia, the national body for oyster grower advocacy, research and development, identified investigating the impacts of climate change on the oyster industry and implementing adaptation measures as a priority in their 2020–25 Strategic Plan (Oysters Australia Strategy Plan 2020–2025). Reflective of this, S. glomerata has become one of the few estuarine aquaculture species undergoing selective breeding for resilience to climate change (Parker et al. 2024). Concurrently, genetic, epigenetic and physiological tools are being employed to identify the underlying mechanisms conferring resilience, leading the way in understanding how climate-resilient organisms cope (Goncalves et al. 2016; Scanes et al. 2017; Stapp et al. 2018; Parker et al. 2024). Climate change-resilient S. glomerata individuals produced through selective breeding are also being trialled for their potential in oyster reef restoration. Current reef restoration efforts in Australia primarily focus on replacing lost substrate to facilitate increased oyster settlement and recruitment. Despite initial success, future oyster reef restoration efforts may face challenges because of interactions among ocean acidification, warming and cumulative pressures (e.g. overharvesting, sedimentation, pollution, introduced pests and disease) that historically led to declines in oyster reefs (Ogburn et al. 2007; O’Connor and Dove 2009). Seeding oyster reefs with climate-resilient oysters could enhance oyster survival and reduce the risk of future restoration failures.
Environmental contamination
Biomonitoring and ecotoxicology
Oysters are widely used as a sentinel species to monitor estuarine pollution because both the larvae and adult stages are exposed to high volumes of seawater in proportion to their size. Studies using oyster embryos as test species have been conducted for over 50 years, with the US EPA documenting its first larval development test almost 30 years ago in 1995. Simultaneously, the first molluscan larval bioassays were developed in Australia on the basis of S. glomerata and Chlamys asperrima (Krassoi 1995). These assays have been commercialised and extensively utilised to assess the impacts of various pollutants, including chemicals, effluents, leachates, groundwater and sediments (Ecotox Services Australasia 2024). S. glomerata larvae have shown sensitivity to metals (Krassoi 1995; Wilson and Hyne 1997), ammonia, petroleum hydrocarbons and dispersants (Smith et al. 2004). Additionally, they have been instrumental in investigating and improving hatchery production for this species (Dove and O’Connor 2007). Indeed, S. glomerata has been the primary species used in most molluscan toxicity assessments in Australia, and despite being a temperate species, it has also been regularly used in tropical toxicity assessments (van Dam et al. 2008).
The filtration capacity of adult oysters offers the potential to strategically deploy adult oysters as ‘passive samplers’ to detect and monitor pollution hotspots in estuaries receiving run-off from intensive agriculture, industrial and urban development, and further test the impacts of flood and fire. There is also potential to expand field translocation/relocation experiments within estuaries to test depuration rates for key contaminants and maximise the use of grow-out and harvest areas within affected estuaries.
Viral and bacterial contamination
While the quantity, treatment and discharge locations of sewage in NSW have changed over the past two centuries, sewage continues to affect NSW coastal waters. Sewage comprises a complex mixture of various pollutants, but it is often the viral and bacterial load that raises the most concern among the public. Oysters, as filter feeders, can accumulate bacteria such as faecal coliforms and Vibrio species, as well as viruses such as norovirus and hepatitis, all of which can pose health risks to humans. This risk has been recognised for many years, with historical references noting that ‘Oysters have been shown to be a very certain source of typhoid’ (Anon. 1902). Oysters have thus long been regarded as indicators of seafood safety and estuarine health, akin to canaries in the mine.
The consequences of viral or bacterial food poisoning can be severe. In 1978, over 2000 cases of norovirus illness were recorded after the consumption of oysters harvested from the Georges River, NSW (Kraa 1990), with a further 1750 cases being recorded in 1990 (Bird and Kraa 1992). Tragically, in 1996–97, Australia experienced its largest recorded outbreak of hepatitis A following the consumption of oysters from Wallis Lake, NSW (Anon. 1997), affecting almost 500 individuals and resulting in one fatality. These events significantly affected the oyster industry, leading to immediate declines in oyster (Fig. 2) and general seafood sales (Handmer and Hillman 2004). Although these incidents were not the fault of the oyster industry, they received extensive media coverage and greatly affected public perceptions of waterway health. However, they also galvanised efforts among oyster farmers and the public to drive change.
Annual production of Sydney rock oysters (1930–2023) and food-borne illness incidents influencing oyster sales: A, 1978 Georges River norovirus outbreak; B, 1990 Georges River norovirus outbreak; C, 1996 Wallis Lake hepatitis outbreak.
A decade after the Wallis Lake outbreak, the response was lauded as ‘a model for how to handle an environmental public health crisis’ (Grennan 2008). Through collaborative efforts involving the oyster industry, fishing industry, local council, businesses and the public, the Wallis Lakes Catchment Management Plan was implemented. This initiative led to significant improvements, including the construction of wetlands to control urban water quality, shoreline fencing for riparian protection, and rehabilitation of acid sulfate soils in wetlands. Furthermore, it paved the way for NSW’s first coastal catchment initiative to enhance water quality (Grennan 2008), demonstrating a successful public health response to an urgent environmental issue. Not only did this protect public health and enhance the environment, but it also facilitated the recovery and prosperity of the local oyster industry (Kardamanidis et al. 2009).
Commercial oyster production and the preservation of estuarine and marine environments are inherently intertwined. Today, the classification of NSW oyster-producing estuaries is regulated under the NSW Food Act 2003, Food Regulation 2015 (see https://legislation.nsw.gov.au/view/html/inforce/current/sl-2015-0622) and the Food Standards Australia New Zealand (2025), with assessments based on potential contamination risks (Australian Shellfish Quality Assurance Advisory Committee 2024). Since the establishment of the NSW Shellfish Program in 2003, up to 30 estuaries have undergone continuous and routine monitoring, co-funded by the NSW government and the industry. This program constitutes one of the most extensive environmental contamination monitoring efforts in NSW. Trained shellfish industry samplers, supported by local industry committees, conduct dedicated sampling regimes to ensure the safety and quality of shellfish products while also contributing positively to environmental conservation. On average, ~7000 microbiological environmental samples are collected and analysed annually, including tests for E. coli in shellfish meat and faecal coliforms in water, serving as primary indicators of potential microbial contamination, including sewage impacts.
In addition to general E. coli monitoring, microbial source tracking of bacterial estuarine water contamination (human, avian, bovine; Geary et al. 2015; Ajani et al. 2024) in key S. glomerata-producing estuaries is underway, with over 11,000 samples having been collected in the past 5 years alone (Ajani et al. 2024). This enhanced testing has provided greater insights into food safety risks and helped identify at-risk areas. Where E. coli from human sources are apparent, targeted efforts are directed towards addressing failing septic or sewerage systems and supporting network upgrades. Similarly, high levels of bovine faecal coliforms have highlighted regions at risk of riparian damage from cattle and promoted remediation through improved stock management practices and fencing upgrades.
Polycyclic aromatic hydrocarbons
Polycyclic aromatic hydrocarbons (PAHs) constitute a diverse group of organic compounds formed through the incomplete combustion of organic materials and various natural processes, such as carbonisation (World Health Organization 1998). Concerns regarding the impact of PAHs on aquatic ecosystems have long been recognised (Anon. 1940). Many PAHs exhibit high lipophilicity, leading to bioconcentration factors exceeding 930 in fish and 130,240 in Daphnia (Canadian Council of Resource and Environment Ministers 1987). Given their threat to a wide array of aquatic organisms (Australian and New Zealand Environment and Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand 2000) and human health, the occurrence of PAHs in oysters is routinely monitored.
Aquatic organisms face exposure to PAHs from numerous sources. Although oil refineries have long been feared as significant contributors (Anon. 1940), they are not the sole concern. Recent bushfires in New South Wales (NSW) have introduced substantial ash into coastal waterways, and activities such as farming and recreational boating with two-stroke motors pose additional risks. Amidst this, the historical use of coal tar and creosote to safeguard wooden maritime structures against marine borers has drawn attention to the oyster industry. Despite the industry’s voluntary shift away from tar-based products for well over a decade, PAHs persist in the environment, with a considerable legacy of tar-treated infrastructure on land and in certain NSW estuaries. Consequently, PAH accumulation and its effects on S. glomerata have undergone assessment (Ertl et al. 2016a; Melwani et al. 2016). Unlike many other species, the spectrum of PAHs detected in S. glomerata, the correlation between sediment and oyster tissue levels, and their capacity to depurate PAHs have also been scrutinised (Idowu et al. 2020a, 2020b). Furthermore, investigations have expanded to include Australia’s first evaluation of the concentration and distribution of parent and polar PAHs within an aquatic species, encompassing oxygenated PAHs, nitrated PAHs and heterocyclic PAHs (Idowu et al. 2020a). Overall, the threat to S. glomerata and the environment from PAHs remains, but the contribution of the oyster industry to the threat has increasingly reduced.
Metals
The capacity of bivalves to accumulate metals and the potential repercussions for both consumers and the organisms themselves have been well documented (Roesijadi 1996). Consequently, monitoring for metal contamination in oysters has been established in the USA for over 50 years (Lauenstein et al. 1990) and for over three decades in S. glomerata populations in Australia (Scanes 1996). Large-scale routine monitoring of metals, alongside PAHs and pesticides, in S. glomerata has been conducted triennially since the 1990s across all major oyster-producing areas in NSW. While general monitoring is increasing, this program stands as one of the most extensive of its type for aquatic life within NSW estuaries.
Numerous studies have examined the impacts of a broad range of metals on various life stages of S. glomerata (Table 1), collectively informing and advocating for estuarine protection. A notable instance is tributyltin (TBT), an antifoulant used on boats. As early as the mid-1980s, international concerns regarding the effects of TBT on oysters were raised (Alzieu et al. 1986), and subsequent research confirmed its threat to S. glomerata. Correlations between abnormal shell growth and recreational boating were observed in 1987 (Scammell 1987), followed by evidence demonstrating the adverse effects of TBT on shell growth, deformity rates and survival (Scammell 1992). In 1998, the Australian federal government banned the use of TBT on vessels repainted in Australia, specifically acknowledging the detrimental effects on marine organisms such as oysters (House of Representatives Committees 2003).
| Metal | Authors | Examples of impacts detected | |
|---|---|---|---|
| Iron (Fe) | Dove and Sammut (2007a, 2007b) (A) | Together with reduced pH and elevated Al, Fe was associated with reduced growth and survival, and thinner shells in adults (Dove and Sammut 2007a). | |
| Copper (Cu) | Wisely and Blick (1967)(L), Nell and Holliday (1986)(L), Butterfield (1987)(S), Muralidharan et al. (2012), Taylor et al. (2013) (A), Yingprasertchai et al. (2017) (L), Ertl et al. (2016b) (A), Yingprasertchai et al. (2019) (A) and Scanes et al. (2018) (A) | Elevated larval mortality, (Wisely and Blick 1967), and reduced settlement and survival. Tissue-specific changes in adult transcriptomes increased metallothionein expression (Ertl et al. 2016b) and a reduction in defensin (Taylor et al. 2013). Metal dependent changes in the proteome of adult oysters, specifically including histones (Muralidharan et al. 2012). | |
| Lead (Pb) | Butterfield (1987) (S), Avery et al. (1996) (A), Muralidharan et al. (2012) (A), Taylor et al. (2013) (A) and Jamal et al. (2022) (A) | Metal dependent changes in the proteome of adult oysters, including NADH dehydrogenase (Muralidharan et al. 2012). | |
| Zinc (Zn) | Wisely and Blick (1967) (L), Butterfield (1987) (S), Muralidharan et al. (2012) (A), Taylor et al. (2013) (A), Lee et al. (2015) (A), Yingprasertchai et al. (2017) (L), Yingprasertchai et al. (2019) (A) and Jamal et al. (2022) (A) | Elevated larval mortality (Wisely and Blick 1967). Increased adult metallothionein expression (Yingprasertchai et al. 2019). Metal dependent changes in the proteome of adult oysters, specifically including tubulins and histones (Muralidharan et al. 2012). | |
| Tin (Sn) | Batley et al. (1989) (A) | Reduced growth and shell deformity in adult oysters. | |
| Aluminium (Al) | Wilson and Hyne (1997) (L), Dove and Sammut (2007b) (A) and Jamal et al. (2022) (A) | Disruption in embryonic development (Wilson and Hyne 1997) with higher mortality, reduced condition index and reduced growth in adults (Dove and Sammut 2007b; Jamal et al. 2022). | |
| Cadmium (Cd) | Ward (1982) (A), Taylor et al. (2013) (A), Schmitz et al. (2015) (A) and Yingprasertchai et al. (2019) (A) | Increased expression of metallothionein (Yingprasertchai et al. 2019), and HSP90, and a reduction in defensin (Taylor et al. 2013) in adults. Reduced total antioxidant capacity, increased lipid peroxidation and lysosome destabilisation (Schmitz et al. 2015). | |
| Mercury (Hg) | Wisely and Blick (1967) (L) | Elevated larval mortality (Wisely and Blick 1967). | |
| Nickel (Ni) | Jamal et al. (2022) (A) | Increased flesh Ni concentrations correlated with reduced body weight (Jamal et al. 2022). | |
| Magnesium (Mg) | Jamal et al. (2022) (A) | Increased flesh Mg concentrations correlated with reduced condition index (Jamal et al. 2022). | |
| Silver (Ag) | Carrazco-Quevedo et al. (2019) (A) | Increased DNA damage, and elevated lipid peroxidation and glutathione reductase in adults. |
The success of TBT control was evident in the recovery of S. glomerata populations and the return of the ecosystem services they provide (Fig. 1). Two years after the partial ban of TBT-based antifouling paints for vessels in NSW, assessments conducted in Sydney Harbour showed the absence of reduced growth and shell deformities seen before the ban. Healthy oysters exhibited significantly lower TBT concentrations, nearing the detection limit (0.2 μg Sn kg−1), with previously high tissue concentrations of copper and zinc also substantially reduced (Batley et al. 1992). Surveys conducted between 1995 and 2005 indicated a notable increase in oyster abundance and density, being particularly evident in areas with high shipping activity, suggesting that the TBT ban may have significantly contributed to the resurgence of S. glomerata in the estuary (Birch et al. 2013).
Estuarine acidification caused by outflows from drained landscapes containing acid sulfate soils (ASS) is a recurrent problem in many NSW estuaries, including those used for S. glomerata cultivation. ASS are characterised by soils and sediments containing oxidisable and already oxidised sulfides, predominantly iron pyrite (FeS2) (White and Melville 1996). Elements commonly associated with ASS-affected waters include SO4, Ca, Si, Mg, Na, Al, K, Fe, Zn, Cu, B, Mn and Cl (Sammut et al. 1996). The concentration of these elements in areas of S. glomerata production depends on the dilution of outflows by upland flows, mixing with estuary waters, and the pH-dependent solubility of the element, particularly Zn, Al and Fe (Sammut et al. 1996). In the 1990s, the S. glomerata industry first linked acidic, floodplain outflows with poor oyster production, prompting action from government authorities and scientists. Studies demonstrated that ASS-affected waters detrimentally affected the survival, growth and reproduction of S. glomerata (Dove and Sammut 2007a, 2013). Exposure to ASS-affected waters resulted in changes in the gills and mantle of S. glomerata, reduced filtration rates because of acid and Al gill damage, and Fe accumulation on gill surfaces (Dove and Sammut 2007b). Iron precipitates could also coat the substrate of the intertidal zone, affecting S. glomerata natural recruitment patterns (Bishop 2000), reducing wild oyster populations and the ecosystem services they provide.
Further examples of S. glomerata driving impactful research followed the recent catastrophic bushfires in NSW, including the ‘black summer’ fires, which raised concerns over the impact of ash on estuarine environments. These concerns were exacerbated by the potential for increased incidence and severity of fires with climate change. Bushfires can volatilise nutrients and metals, including Fe, Mn, As, Cu, Al, Pb, Cr Cd and Ni (Ito et al. 2020; Barros et al. 2022), leading to significant influxes into estuaries. Long-term, real-time environmental monitoring established for major S. glomerata production estuaries in 2018 (Ajani et al. 2024), coupled with regular oyster tissue and phytoplankton sampling, is now providing unique and valuable insights into the impacts of bushfires on estuarine biota. Specifically, the accumulation of Fe in oysters and its impacts on algal blooms, including potentially harmful Dinophysis spp. (Penny Ajani, pers. comm., 2024). These data and preserved biological samples now serve as a valuable archive for investigating and understanding new and emerging threats to NSW estuaries.
Typically, studies delving into the impacts of metals and metalloids on aquatic organisms focus on individual elements in isolation, or at most, consider simultaneous exposure to two or three related metals (Pan et al. 2015). However, organisms in the environment face mixtures of metals, which may be elevated in contaminated areas or following events such as floods and fires. Chronic exposure to certain metals has been demonstrated to enhance the bioaccumulation of other metals or metalloids in oysters (Liu and Wang 2014). A recent investigation in the Richmond River showed that combinations of multiple elements were robust predictors of S. glomerata health (Jamal et al. 2022). Specifically, the amalgamated concentrations of trace elements such as Hg, Ni, Cr, Cu, Cd, or Pb in the flesh exhibited strong correlations with oyster condition index and mortality rates across various sites, whereas individually, these elements did not display significant relationships. This study underscores the importance of the consideration of the synergistic impacts of all stressors, and that heightened mortality and diminished physical condition within natural S. glomerata populations can serve as valuable indicators of potential chronic pollution, aiding in prioritising areas for further investigation.
Overall, the study of metal impacts is one of the clearer examples of S. glomerata’s role in protecting our estuarine ecosystems. The comparative number of studies (Table 1) and their continuation for over 50 years is testament to their importance. The understanding developed has led to the use of oysters as bioindicators and in ecotoxicology assays to monitor pollutant inputs to protect estuaries. Critically this work has underpinned change, as was the case for TBT, and that has to led wider ecosystem benefits.
Pesticides
Efforts to increase food security, along with rapid growth in the human population, have led to increased production and use of a diversity of synthetic pesticides (Popp et al. 2013), including herbicides, insecticides and fungicides. Notably, in Australia, pesticide use is estimated to have increased 255% from 17,866 Mg in 1990 to 63,416 Mg in 2020 (Ritchie et al. 2022). These chemicals, when applied on land, can seep into water bodies and accrue in estuarine environments through surface run-off, spray drift and groundwater infiltration (Shishaye et al. 2021; Laicher et al. 2022; Warne et al. 2023). S. glomerata has been pivotal in our endeavours to monitor pesticide pollution and has been the subject of numerous studies scrutinising pesticide impacts on aquatic organisms.
The ability of bivalves to accumulate some chemical contaminants in their flesh makes them useful for environmental monitoring of pesticides. S. glomerata have been used to detect pesticide residues since 1970, when chlorinated hydrocarbon pesticide residue concentrations were monitored over 2 years in Morton Bay (Clegg 1974). Subsequently, Scanes (1996) developed the NSW Oyster Watch program where S. glomerata was deployed in Sydney ocean effluent outfalls to detect contaminants, whereas others, such as Hunter Water, have undertaken similar exercises (Andrew-Priestly et al. 2012). Scanes and Gibson (1996) also sampled wild S. glomerata to investigate organochlorine residues more broadly in estuaries on the NSW coast. An experimental field study using S. glomerata demonstrated the uptake of several organochlorine compounds from a contaminated location in Sydney Harbour, followed by depuration in a clean location (Scanes 1997). The biological half-lives of these pesticides were modelled and employed to inform the Mussel Watch and NSW EPA Oyster Watch programs for biomonitoring. Pesticide run-off into water bodies also presents risks to human consumer health. Consequently, under the NSW Shellfish Program, ongoing triennial surveys for persistent organic pollutants and pesticides have been conducted since 1999. This monitoring has indicated that oysters supplied for consumption have not been significantly affected by pesticide run-off. Nonetheless, this monitoring program persists while the oyster industry continues harvesting from estuarine environments, offering ongoing surveillance to safeguard both the industry and the estuarine ecosystem.
In the 1990s, a new class of neuroactive insecticides called neonicotinoids was registered for agricultural use and these rapidly became the most widely used insecticides worldwide (Ewere et al. 2021b). Extremely high environmental concentrations of the neonicotinoid imidacloprid (up to 294 μg L−1) were detected in non-oyster-producing intensive agricultural catchment draining into the Solitary Islands Marine Park in northern NSW (Laicher et al. 2022). Even so, S. glomerata uptake and depuration of imidacloprid was demonstrated and its sublethal effects elucidated through transcriptomics (Ewere et al. 2019a). At environmentally relevant concentrations, imidacloprid was found to affect haemocyte aggregation, haemolymph protein expression, acetylcholine esterase and oxidative stress enzyme activity of S. glomerata (Ewere et al. 2019b, 2020). Furthermore, exposure to both imidacloprid and a commercially available formulated product, caused alterations in fatty acid biosynthesis, leading to a reduction in healthy polyunsaturated fatty acids and thus lowering the nutritional quality of the flesh (Ewere et al. 2019b, 2020). The co-ingredients in commercial pesticide products, such as surfactants, dyes and antifoaming agents, are rarely considered in ecotoxicology testing, but can modify the bioavailability and toxicity of pesticides (Mesnage and Antoniou 2018).
Within complex agricultural and urban catchments, surface run-off is likely to transport numerous pesticides and associated contaminants simultaneously into estuarine environments. A recent study in the Richmond River on the North Coast of NSW found wild S. glomerata to be effective passive samplers, accumulating 13 different pesticides, compared with just five in water samples collected concurrently from the same location (Jamal et al. 2024). Benomyl, a pesticide banned in Australia, was detected, triggering further investigation by the NSW EPA. Chlorpyrifos, an insecticide currently subject to regulatory action restricting its use in Australia (Australian Pesticide and Veterinary Medicine Authority 2023), was also detected in the oysters, but not in the water samples (Jamal et al. 2024). Furthermore, pesticides, including the herbicides atrazine, diuron and hexazinone, that have been banned, severely restricted or not approved for use in the European Union because of ubiquitous water contamination concerns, were detected. These pesticides have also been found in surface run-off and groundwater in intensive agricultural catchments of the Great Barrier Reef (Lewis et al. 2009; Shishaye et al. 2021; Warne et al. 2023), thus highlighting the need for regulatory review of their use in Australia. None of the pesticides detected in S. glomerata by Jamal et al. (2024) have maximum residue limits (MRLs) for seafood and five do not have MRLs for meat products. Although they may not have been expected to contaminate seafood or meat, oysters have led the way and chlorpyrifos, atrazine, diuron and hexazinone have now been added to routine monitoring programs in NSW. Collectively, the pesticides found in S. glomerata represent 10 different chemical classes with seven distinct modes of action (Jamal et al. 2024), underscoring the potential for cumulative stress from synergistic or accumulative effects.
Endocrine disrupting chemicals (EDCs)
EDCs encompass a diverse range of environmentally persistent synthetic chemicals that mimic the structure of endocrine hormones and induce similar effects on accumulation by organisms. Among these compounds are oestrogenic contaminants, structurally resembling the female sex hormone oestrogen and capable of mimicking its effects. Examples include ethinyloestradiol (EE2), a component of contraceptive pills, bisphenol A (BPA) and breakdown products of alkylphenol ethoxylates such as nonylphenol (NP) and octophenol (OP). Oestrogenic contaminants enter water bodies from various sources, including industrial discharge and effluents from wastewater treatment plants, and are frequently detected in Australian wastewater and receiving waters (Leusch et al. 2005; Tan et al. 2007; Scott et al. 2017; Islam et al. 2021). Although oestrogenic EDC concentrations in Australian waterways are lower than those internationally reported, they still exceed predicted no-effect concentrations for various aquatic biota (e.g. 0.1 L−1 for EE2, Tran et al. 2019). With total effluent estimates from individual wastewater treatment plants in NSW reported at a staggering rate of 10,585 ML year−1, and most of these effluents directly being discharged into marine or estuarine environments, potential effects raise significant concern (Islam et al. 2021).
Several studies employing vertebrate models have been made, predominantly examining the role of EDCs in feminisation and vitellogenin induction in fish (e.g. Batty and Lim 1999; Codi King et al. 2008). Vitellogenin, a gonadal egg-yolk protein precursor, is an appropriate oestrogenic biomarker, because its production increases on exposure to oestrogens (Andrew et al. 2008). Vitellogenin offers a measure of the presence of complex oestrogenic mixtures where individual contaminants may be unknown and can demonstrate biologically significant impacts on the organism of interest. Remarkably, vitellogenin expression in males has been observed, serving as direct evidence of endocrine disruption because males typically do not produce vitellogenin under normal conditions (Tran et al. 2019). Exposure to EE2 and NP increases gonadal vitellogenin production up to three- and two-fold respectively, in female S. glomerata, and significant increases in vitellogenin were also observed in males exposed to 50 ng L−1 EE2 (Andrew et al. 2008). Further experiments showed that S. glomerata adults exposed to environmentally relevant concentrations of EE2 (0, 6.25, 12.5, 25 or 50 ng L−1) for 49 days exhibited dose-dependent increases in vitellogenin concentrations for both females and males (Andrew et al. 2010). Histological examination of gonads indicated a significant shift towards females over time, with the presence of intersex (ovotestis) individuals suggesting that oestrogenic exposure can facilitate the transition of protandric males towards female gametal status. These laboratory studies demonstrated the potential of S. glomerata as a biomonitor for detecting exposure and impacts of oestrogenic EDCs. In field studies, oysters deployed adjacent to an ocean outfall with effluent containing oestrogenic compounds exhibited elevated vitellogenin gene and protein expression compared with numerous reference deployments in the region (Andrew-Priestly et al. 2012). Additionally, females at the ocean outfall site showed more advanced stages of oocyte development than those at reference locations.
Perfluoroalkyl substances
Among the emerging threats to NSW estuaries and oyster cultivation in NSW are the increasing number of sites contaminated with perfluoroalkyl substances (PFAS). PFAS are persistent environmental pollutants used in a broad range of industrial applications and consumer goods that are now of worldwide concern for their potential adverse effects on human health, such as cardiovascular disease and cancer (Lindstrom et al. 2011). PFAS were initially detected in S. glomerata in Sydney Harbour (Thompson et al. 2011), but oyster farming did not occur in the area at the time, and commercial and recreational fishing had previously been banned (Roach et al. 2009). The gravity of the situation became more apparent when the first impacts on farmed oysters emerged in Port Stephens, one of the largest oyster-producing estuaries in NSW. The Tilligerry Creek farming area was affected by PFAS-contaminated runoff from a nearby airfield. Prompt testing commenced, with S. glomerata among the initial species monitored. Perfluorooctane sulfonate (PFOS) was detected in both S. glomerata and, the Pacific oyster, Crassostrea gigas. Fortunately, direct harvesting of oysters from the area was prohibited without depuration or relocation to an approved open harvest area for a period of 14 days. Both methods were found to result in significant reductions in oyster tissue PFOS concentrations (O’Connor et al. 2018). The level of concern for the environment and the industry was so high that this research, including depuration monitoring, was completed within 3 weeks of notification of the PFAS threat. Preliminary results were promptly disseminated to industry stakeholders and the public, and despite allaying some concerns, they added impetus and urgency for investigation in other estuarine species.
Microplastics
Microplastics are recognised globally as a threat to the marine environment, and discussions on their impacts on marine organisms, and ultimately on their consumers, are widespread (Carbery et al. 2018). Once again, research has utilised S. glomerata as a model organism to assess the risk to estuarine organisms in NSW and, in this case, to explore the response of the oyster industry to this threat.
Like many marine organisms, S. glomerata has been found to ingest and absorb microplastics, both in laboratory settings (Scanes et al. 2019) and when sampled from Australian estuaries (Wootton et al. 2022; Boyd 2023). On ingestion, microplastics may cause physical harm and serve as vectors for a variety of chemicals leaching from the plastic particles or adsorbed onto their surfaces, subsequently being released (Wright et al. 2013; Carbery et al. 2020; Bhagwat et al. 2021a, 2021b). Furthermore, the microbiome that swiftly develops on the surface of microplastic particles varies with plastic type, and can pose additional risks to oysters (Bhagwat et al. 2021a, 2021c) and other estuarine species.
As NSW oyster farmers transitioned from tar-treated timber sticks and trays to recyclable plastics in response to the threats posed by PAHs, the potential for oyster exposure to microplastics increased. Despite the minimal plastic usage by the industry compared with other sources, it has actively supported microplastic research. Efforts have commenced to monitor the degradation of plastics commonly employed in the oyster industry, to better comprehend the specific threats posed and aid in the selection of the most suitable plastic types for use in cultivation equipment (Bhagwat et al. 2021a). In a research first, the impact of long-term plastic aging through weathering and biofouling on plastic behaviour and fate in the marine environment utilised S. glomerata cultivation equipment to characterise contaminant profiles and bacterial communities. Using 10-year-old plastic infrastructure from intertidal, subtidal and sediment-buried segments of an oyster lease, assessments evaluated the risk to oysters, their consumers and the broader environment from microplastics of all origins finding high-density polyethylene plastics harboured high concentrations of metal(loid)s, PAHs and PFAS. Metagenomic analysis showed that the bacterial composition at the plastic surface differed by habitat type, and included potentially pathogenic bacterial taxa including Vibrio, Shewanella and Psychrobacter (Bhagwat et al. 2021a). This research helped broaden the understanding of the wider threat posed by microplastics beyond their accumulation in the food chain, to include their role as a vector for contaminants through the ecosystem.
Oyster industry
The success of efforts to restore and maintain estuarine health hinges on the values held by the community and stakeholders, their collective vision, and their enduring dedication to sustained action and investment (Thom et al. 2023). In this context, the NSW oyster industry emerges as a pivotal player in shaping this shared community vision. With its longstanding presence, the oyster industry has become deeply ingrained in the identity of many coastal communities in NSW, and the unwavering passion of farmers for both the industry and the waterways it relies on is widely recognised (Barclay et al. 2016; Fig. 3).
When surveying public perceptions of aquaculture in NSW, where oyster production dominates, Barclay et al. (2016) uncovered a high level of community trust in the value of aquaculture, owing to its social, economic and environmental contributions. Specifically for the oyster industry, the public expressed concerns about threats posed by residential development, river pollution, flooding, acid sulfate soils and toxic algal blooms. Reflecting the community belief in the interconnectedness of healthy oysters and healthy rivers, Barclay et al. (2016) found that the industry played a significant role in promoting environmental awareness, particularly in areas such as managing estuarine health, improving water quality and understanding estuarine ecology.
The ongoing efforts of oyster farmers to safeguard the resources they depend on are evident through their proactive identification of threats, advocacy efforts and adherence to self-imposed environmental protection measures outlined in their Environmental Management Systems (EMS), which are all publicly available (see https://www.nswoysters.com.au/environmental-management-systems.html). These EMS are estuary-specific and encourage farmers to work with other stakeholders to actively contribute to marine environmental protection and conservation through pollution reduction, habitat protection and sustainable resource management. Moreover, their commitment to adopting best practice guidelines underscores their dedication to environmental stewardship.
The future and natural recovery
The outlook for the S. glomerata industry and research remains promising, with a continued focus on enhancing estuarine environmental health. Economic incentives for research are growing, paralleling the increasing value of the industry (now exceeding A$80 million, NSW DPI, unpubl. data), which rivals the combined value of all commercial fisheries in NSW (BDO EconSearch 2023). Research priorities are evolving to address emerging threats in estuaries, including the complex interplay of stressors such as climate change, and flood and fire-related contaminants.
Whereas the NSW government remains committed to selective breeding for S. glomerata, the focus has broadened beyond commercial priorities to encompass traits relevant to broader environmental recovery and longevity, such as ocean acidification and warming resistance. Research efforts increasingly target the restoration of once-extensive oyster reefs (Cole et al. 2022). Projects aim to understand factors facilitating reef establishment and expansion, improve interventions in aquatic environments to support ecosystem maintenance and develop direct reef restoration techniques (Hart et al. 2024; Leong et al. 2024). Moreover, research continues to quantify the ecosystem benefits derived from reefs (Cole et al. 2022; Filippini et al. 2023), whether for community or commercial purposes (Bishop et al. 2023). Research on the ecosystem benefits of commercial oyster leases is also warranted; although natural oyster reef ecosystems have been largely absent from NSW estuaries for over a century (McAfee et al. 2022), active oyster farming has ensured that substantial populations of oysters have been maintained in most large waterways. It is important to understand better the role oyster farming can play in delivering ecosystem services such as improved water quality, and habitat provision to preserve the diversity and abundance of native estuarine species.
Innovative projects utilising eco-engineering techniques are underway to enrich native species biodiversity through habitat enhancement (Strain et al. 2018; Bishop et al. 2022). For instance, the ‘Living Seawalls: Bring Back the Sydney Rock Oyster’ project has demonstrated the benefits of seeding oysters onto engineered surfaces, resulting in increased abundance, richness and diversity of other taxa, as well as enhanced suspended particle removal rates from the water (Vozzo et al. 2021).
Although awareness of the scale of loss of S. glomerata reefs is by no means new, dedicated restoration efforts for Australian shellfish reefs began only in 2015 (McAfee et al. 2022). Importantly, the sustained research and environmental monitoring of the aquaculture industry have influenced government management of coastal water quality (Schrobback et al. 2014) and generated the knowledge to underpin restoration efforts (McAfee et al. 2022). Currently, 14 reef restoration projects are underway across southern Australia, with plans to expand to 60 projects by 2030 (The Nature Conservancy 2024).
In addition to reef restoration, ‘oyster gardening’ has been a popular initiative elsewhere in the world (Brumbaugh and Coen 2009; Oesterling and Petrone 2012), allowing citizen scientists to broaden the scale and scope of restoration activities. It can be achieved cheaply and allows participants to contribute to community needs (Toomey et al. 2020; Agnello et al. 2022). This cost-effective approach not only provides adult oysters for restoration programs, but also supports other ecosystem services such as habitat provision for fishes and invertebrates, while fostering community involvement (Boström-Einarsson et al. 2022). Australia’s first oyster gardening program began in a canal estate on Bribie Island in Moreton Bay in 2016–17, and was undertaken using S. glomerata that was later used in nearby reef restoration initiatives (Boström-Einarsson et al. 2022).
Aligned with the oyster industry commitment to sustainability and maintaining social license, efforts are underway to map its impacts and quantify the ecosystem benefits of farming S. glomerata. These assessments draw on decades-old physiological studies of S. glomerata, such as those of Bayne and Svensson (2006), but are expanding on this work and considering them in a broader ecosystem services framework. For example, the role of the NSW oyster industry in nutrient removal from estuaries has recently been assessed, with an estimated A$5.2 million worth of nitrogen and phosphorus being assimilated (BDO EconSearch 2023). The value of S. glomerata farm infrastructure as habitat for other marine organisms has been confirmed, with rack and basket culture both found to support at least as many species of fish as adjacent biogenic habitats such as oyster reefs, seagrass and mangroves (Martínez-Baena et al. 2022). These authors noted that the ecosystem services S. glomerata should be considered in estuarine habitat enhancement, conservation and restoration, and the oyster industry is engaging further with the concept of regenerative aquaculture to promote net positive environmental outcomes, as explored by Alleway et al. (2019) and Gentry et al. (2020).
Conclusions
S. glomerata is unique among the many animals that inhabit NSW estuaries. It is a keystone species in the ecology of our estuaries, it forms the basis of NSW’s most valuable fishery, is NSW’s oldest aquaculture industry, and is considered one of our greatest gastronomic delicacies. In the minds of the NSW public, it has been strongly linked with the health of our estuaries for 150 years. Whether S. glomerata is ‘the canary in the mine’, the ‘doormat of the estuary’ (Ogburn 2011) or the ‘lungs of healthy estuaries’ (Diggles 2015), they have been, and most likely will continue to be, a focus for research and a rallying point for the protection of one of NSW’s most valuable assets, namely, its estuarine ecosystems and inhabitants.
Globally, S. glomerata farming is not unique among mollusc aquaculture industries for its wider social, economic and ecological contribution. The body of research around other commonly cultivated species such as Crassostrea gigas and C. virginica, is substantially larger. These species have similarly been used for pollutant impact evaluations (Alzieu et al. 1986), biomonitoring (Lauenstein et al. 1990) and climate-change impact assessment (Gazeau et al. 2013). C. virginica has been the subject of reef restoration efforts for decades (Howie and Bishop 2021), which are supported by an increasing public awareness of the ecosystem services provided by oysters. However, aquaculture still faces issues with social license and as we develop concepts such as regenerative aquaculture (Alleway et al. 2019), the full extent of the benefits arising from commercial interest in a species need to be elaborated. Here, we have tried to describe the range of benefits that have arisen from the S. glomerata industry, to assist industry in furthering social license and in the hope that it may encourage other industries to chronicle their contributions.
Data availability
All data used in the preparation of this review was obtained from published literature listed in the references.
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