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Oyster Reefs at Risk and Recommendations for Conservation, Restoration, and Management
Abstract and Figures
Native oyster reefs once dominated many estuaries, ecologically and economically. Centuries of resource extraction exacerbated by coastal degradation have pushed oyster reefs to the brink of functional extinction worldwide. We examined the condition of oyster reefs across 144 bays and 44 ecoregions; our comparisons of past with present abundances indicate that more than 90% of them have been lost in bays (70%) and ecoregions (63%). In many bays, more than 99% of oyster reefs have been lost and are functionally extinct. Overall, we estimate that 85% of oyster reefs have been lost globally. Most of the world's remaining wild capture of native oysters (> 75%) comes from just five ecoregions in North America, yet the condition of reefs in these ecoregions is poor at best, except in the Gulf of Mexico. We identify many cost-effective solutions for conservation, restoration, and the management of fisheries and nonnative species that could reverse these oyster losses and restore reef ecosystem services.
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... The eastern oyster (Crassostrea virginica) is a keystone species that builds reefs in estuaries along the western North Atlantic. They regulate water quality, create habitat for over 300 species, and provide critical ecosystem services [77][78][79][80]. However, over 90% of oyster reefs have been lost in North America since their peak harvest days in the 1800s [77,81,82]. ...
... They regulate water quality, create habitat for over 300 species, and provide critical ecosystem services [77][78][79][80]. However, over 90% of oyster reefs have been lost in North America since their peak harvest days in the 1800s [77,81,82]. The eastern oyster is a valuable species for investigating how plastic debris may impact sexual development. ...
The degradation of marine plastic debris poses a threat to organisms by fragmenting into micro- and nano-scale pieces and releasing a complex chemical leachate into the water. Numerous studies have investigated harms from plastic pollution such as microplastic ingestion and exposure to single chemicals. However, few studies have examined the holistic threat of plastic exposure and the synergistic impacts of chemical mixtures. The objective of this study was to measure changes in gene expression of gill and gonadal tissue of the eastern oyster (Crassostrea virginica) in response to plastic debris exposure during their first year, using RNA-seq to explore multiple types of physiological responses. Shell and polyethylene terephthalate plastic were used as substrate for the metamorphosis of larval oysters in a settlement tank. Substrate pieces were then transferred to metal cages and outplanted in pairs – shell cage and plastic cage – onto restoration reefs in the St. Mary’s River, Maryland, USA. After 10 months of growth, the oysters were collected, gill and gonadal tissue removed, and sex identified. The tissues of six oysters from each sex and substrate type were then analyzed in RNA-seq. Both gill and gonadal tissue samples had altered expression of immune and stress-response genes in response to plastic exposure. Genes upregulated in response to plastic were enriched for gene ontology functions of proteolysis and fibrinolysis. Downregulated genes were involved in shell biomineralization and growth. One male oyster exposed to plastic had “feminized” gene expression patterns despite developing mature sperm, suggesting plastic leachate can alter gene expression and shift protandric individuals to develop as females. Plastic pollution may therefore reduce shell growth, initiate immune and stress responses, alter sex differentiation, and impact reproductive output of eastern oysters through changes in transcription.
... Globally, historical oyster reefs decreased by approximately 85% (Beck et al., 2011). Reductions in global oyster populations were attributed to several factors, including disease (Haskin and Ford, 1982;Andrews, 1988;Petton et al., 2021), overharvest (Rothschild et al., 1994) and climate change (McFarland et al., 2022;Heo et al., 2023;Neokye et al., 2024). ...
Oysters are ecologically and commercially important species that require frequent monitoring to track population demographics (e.g. abundance, growth, mortality). Current methods of monitoring oyster reefs often require destructive sampling methods and extensive manual effort. Therefore, they are suboptimal for small-scale or sensitive environments. A recent alternative, the ODYSSEE model, was developed to use deep learning techniques to identify live oysters using video or images taken in the field of oyster reefs to assess abundance. The validity of this model in identifying live oysters on a reef was compared to expert and non-expert annotators. In addition, we identified potential sources of prediction error. Although the model can make inferences significantly faster than expert and non-expert annotators (39.6 s, h, h, respectively), the model overpredicted the number of live oysters, achieving lower accuracy (63\%) in identifying live oysters compared to experts (74\%) and non-experts (75\%) alike. Image quality was an important factor in determining the accuracy of the model and the annotators. Better quality images improved human accuracy and worsened model accuracy. Although ODYSSEE was not sufficiently accurate, we anticipate that future training on higher-quality images, utilizing additional live imagery, and incorporating additional annotation training classes will greatly improve the model's predictive power based on the results of this analysis. Future research should address methods that improve the detection of living vs. dead oysters.
... Gambar 10.1 Jangkauan area dan hilangnya ekosistem pesisir pada masa lalu dan yang diprediksi kedepannya (Sumber : CSIRO. 1 Beck et al. 2011;2 Bunting et al. 2018;3 Goldberg et al. 2020;4 Mcowen et al. 2017;5 Murray et al. 2018;6 Nienhuis et al. 2020;7 Rogers et al. 2020;8 UNEP 2020;9 Vousdoukas et al. 2020;10 Wernberg et al. 2019.) ...
Buku ini mengidentifikasi masalah yang umum terjadi pada
ekosistem pesisir, dan menjelaskan langkah-langkah perencanaan yang
sistematis untuk melaksanakan restorasi. Teknik restorasi dengan
menggunakan tanaman mangrove, pembangunan terumbu karang
buatan, serta rehabilitasi padang lamun menjadi fokus utama dalam buku
ini, dilengkapi dengan strategi pemberdayaan masyarakat yang krusial
dalam mendukung keberhasilan restorasi.
Interaksi kompleks antara manusia dan lingkungan di kawasan
pesisir menjadi topik penting yang kami eksplorasi, sambil menyoroti
tantangan dan hambatan yang sering kali dihadapi dalam implementasi
proyek restorasi. Inovasi dan pengembangan teknik baru, serta peran
kunci perempuan nelayan dalam menjaga dan memulihkan hutan bakau,
juga menjadi bagian integral dari diskusi kami
... Despite once being dominant features of coastal ecosystems worldwide, oyster reefs have been pushed to the brink of extinction over the last two centuries due to natural resource extraction efforts. Shockingly, more than 85% of the planet's oyster reefs have disappeared during this period (Beck et al., 2011). Because coastal ecosystems are disproportionately vulnerable to the disruptive impacts of climate change and human development, returning oyster reefs to their prior ecosystem states is often an infeasible or inappropriate goal (Howie & Bishop, 2021). ...
... Oysters are widely distributed in world oceans and play important roles in coastal and estuary ecology. They are filter-feeders and habitat engineers, providing critical ecological services to marine ecosystems (Beck et al. 2011;Grabowski et al. 2012). As sessile species thriving in intertidal zones of estuaries where environmental conditions fluctuate greatly, oysters are resilient and provide good model species for studying environmental adaptation of sessile marine invertebrates. ...
The Kumamoto oyster, Crassostrea sikamea, is a marine bivalve naturally distributed along the coasts of southern China and southern Japan, with a hatchery population that has been under domestication in the United States since its introduction from Japan in the 1940s. To understand its evolutionary history and environmental adaptation, we produced a chromosome‐level genome assembly of C. sikamea and conducted whole‐genome resequencing of 141 individuals from the US hatchery population and six wild populations from China and Japan. The assembled genome of C. sikamea has a size of 616 Mb covering all 10 chromosomes with a contig N50 of 4.21 Mb and a scaffold N50 of 62.25 Mb. Phylogenetic analysis indicated that C. sikamea diverged from the Crassostrea angulata and Crassostrea gigas clade about 9.9 million years ago. Synteny analysis revealed significant chromosomal rearrangements during bivalve evolution leading to oysters, but remarkable conservation of all 10 oyster chromosomes over ~180 million years, a surprising disparity in chromosomal evolution. Phylogenetic analysis produced three distinct clusters for the US, Japanese, and Chinese populations, with the US population closer to the Japanese population, confirming its origin. No differentiation was detected among the five Chinese populations, indicating strong gene flow. Between the US and Japan populations, 402 genes exhibited selection signals, including three myosin heavy chain genes that were also differentiated in domesticated lines of the eastern oyster, suggesting changes in these genes may be important for domestic production. Among the 768 genes showing selection signals between natural populations of Japan and China, genes related to stress response are most enriched, suggesting responding to environmental stress is critical for local adaptation. These findings provide insights into bivalve evolution and environmental adaptation, as well as useful resources for comparative genomics and genetic improvement of cultured Kumamoto oyster stocks.
... Oysters are important ecological engineers (Jones et al., 1994), but their reefs have suffered substantial global declines since the 1800 s due to water pollution, disease and commercial harvesting (Beck et al., 2011). In Australia, it is estimated that less than 10% of oyster reef habitat remains (Ford & Hamer, 2016). ...
Oyster reef restoration increasingly pursues the goal of enhancing coastal protection that can lead to a reduction in loading on shorelines through flow attenuation of waves and currents. However, flow attenuation is dependent on factors such as reef submergence, width and complexity. Yet the relationship between elements of the oyster reef landscape and flow attenuation is still not fully understood, making it challenging to design nature-based solutions for coastal protection. The topographical roughness characteristics of Sydney rock oyster ( Saccostrea glomerata ) reef surfaces were investigated using spatial statistics extracted from digital elevation models. Oyster agglomerations were classified into three distinct structural classes (Patch I, Patch II and Cluster) to differentiate intra-reef complexity. Patch I types had greater roughness heights (total roughness height, k t = 74 ± 10 mm) than Patch II ( k t = 56 ± 9 mm). Benthic flow instantaneous velocity readings were taken at windward, leeward and on-reef points for each delineated structural class. Of the samples examined, observations were made that oyster beds with higher k t values experienced greater flow reduction. While a direct link cannot be established, with future work, the results of this study can assist in achieving meaningful targets for patch-scale oyster reef restoration substrate.
... Within habitat variations in shell mortality and degradation results in structural and functional diversity, which in turn influences biodiversity (Copertino et al., 2022;Summerhayes et al., 2009). Shellfish reefs have diminished over the past two centuries worldwide, mainly from destructive benthic fisheries and overharvesting (Alleway & Connell, 2015;Beck et al., 2011;Thurstan et al., 2024). Increasing awareness of the socioecological services associated with shellfish reefs including fish production, biofiltration, and shoreline protection has driven growing oyster and mussel reef conservation efforts (Hemraj et al., 2022;Roberts et al., 2023;zu Ermgassen et al., 2020). ...
Extensive bivalve aggregations, including shellfish reefs and beds, influence the structure and functions of coastal environments. In soft-bottom habitats, bivalves contribute consolidated structures which can influence species distributions, often long after bivalve death. Understanding this process is essential to inform habitat management and conservation efforts. Here, we describe how intertidal razor clams Pinna bicolor (Pinnidae) influence fish and invertebrate assemblages within a temperate Australian estuary. Specifically, we assessed how pinnid mortality status (dead and alive) and density influenced assemblage habitat use. Assemblages were assessed using a combination of shell scrapings, infauna cores, sweep nets, unbaited video stations, and squidpops. Evidence from multiple methods demonstrated that pinnids underpinned structural and faunal species diversity in an otherwise homogenous benthic environment. Fauna species abundances varied with pinnid mortality status and density. Pinnid aggregations provided settlement surfaces, refugia, and trophic resources that facilitated a range of sessile and mobile organisms. This benefited fisheries-targeted fish and decapod species which used this habitat for foraging based on video monitoring and predation assays. Additionally, densities of > 10 pinnids m ⁻² optimised the facilitation of benthic and epifaunal habitat functions. Further studies of Pinnidae ecosystems, incorporating broader seascape assessments, will improve knowledge of their habitat use by mobile species. Our results illustrate how Pinna bicolor aggregations can influence intertidal species assemblages, and identified opportunities for improved Pinnidae ecosystem management.
The complex network of prop roots in red mangroves, along with the associated organisms that contribute to this complexity, creates a diverse habitat for various epibiont species. Yet, complexity metrics and their relationship with macro-epibiont community structure have not been assessed in these networks. Here, with proposing a methodology for 3D reconstruction of these assemblages using computed tomography, the structural heterogeneity generated by macro-epibionts on red mangrove prop roots was quantified. Also, the linkage between macro-epibiont structural complexity and their community structure was unraveled. A total of 25 macro-epibiont taxa on prop roots were identified, most of which were calcifiers belonging to bivalves, gastropods, polychaetes, and crustaceans. Surface area and fractal dimension were the most influential complexity contributors in the overall architecture of the macro-epibiont assemblages. Surface area correlated positively with species richness and biomass, while interstitial spaces strongly influenced abundance and inorganic matter content. Our results emphasize the value of surface area and interstitial spaces as the most important structural complexity metrics in determining various aspects of macro-epibiont assemblages on mangrove prop roots. This study can have implications for conservation, biodiversity assessment and studying ecosystem functioning.
Intertidal reefs comprised of the eastern oyster (Crassostrea virginica) are an important habitat type within the estuarine landscape and provide many unique ecosystem services. Within West Galveston Bay (WGB), Texas, this type of reef plays an important ecological role; however, the system’s intertidal reef abundance, structure, and habitat provisions are relatively understudied, and the current spatial extent of these reefs has not been recently quantified. The primary objectives of the study were to identify intertidal oyster reefs utilizing GIS models and sample representative reefs for topographical characteristics, oyster demographics, and the associated benthic macrofauna (ABM) community composition in WGB from August 2019 to February 2020. Secondarily, GIS models and oyster population abundance were utilized to estimate the intertidal oyster abundance in WBG. The total area of intertidal oyster reefs in WGB was estimated to be 818,128 m2, with 59,931 m2 of reefs confirmed through GIS analysis and ground truthing, and the GIS model estimating an additional 758,197 m2 of reef. Through ground truthing, reefs were found to be either shell rakes, consisting of piled shell with minimal three-dimensional structure and oysters, or true intertidal reefs with high reef structure and oyster abundance. High oyster abundance was spatially distributed within the northeastern and southwestern areas of WGB and the total intertidal oyster population, coupling the GIS models and reef sampling, was estimated to be 500 million individual oysters. The ABM community was sparse in terms of richness and diversity, further indicating a lack of structural complexity in most of the reefs within this system. This study demonstrates the importance of coupling field results with GIS modeling to estimate system level population sizes and furthers the understanding of the spatial distributions of intertidal oyster reef to promote management, conservation, and restoration efforts.
The conservation and sustainable use of marine resources is a highlighted goal in a growing number of
national and international policy agendas. Unfortunately, efforts to assess progress, as well as to
strategically plan and prioritize new marine conservation measures, have been hampered by the lack of a
detailed and comprehensive biogeographic system to classify the oceans. Here we report on a new global
system for coast and shelf areas the Marine Ecoregions of the World (MEOW) a nested system of 12
realms, 62 provinces and 232 ecoregions. This system provides considerably better spatial resolution than
previous global systems, while preserving many common elements, and can be cross-referenced to many
regional biogeographic classifications. The designation of terrestrial ecoregions has revolutionized priority
setting and planning for land conservation; we anticipate similar benefits from the creation of a coherent
and credible marine system.
Molluscan aquaculture in China has been growing rapidly in the past decade. China produced 6.4 million metric tons (MMT) of mollusks from aquaculture in 1996, an eightfold increase over that of 1986. At least 32 species of marine mollusks are cultured commercially in China. The 1996 production included 2.3 MMT of oysters, 1.6 MMT of clams (mostly Ruditapes, Meretrix, razor clams, and blood cockles), 1 MMT of scallops, 0.4 MMT of mussels, 700 tons of abalone, and 20 tons of marine pearls. Shandong province is the largest producer of cultured mollusks, followed by Guangdong, Fujian, Liaoning, Guangxi, and Zhejiang provinces (ranked 2-6, respectively). As a generalized pattern, molluscan aquaculture in China is characterized by scallops, abalone, and Manila clams in the northern provinces (Shandong and Liaoning), oysters and pearl oysters in the south (Fujian, Guangdong, and Guangxi), and various clam species in the middle (Zhejiang and Jiangsu). The production technology ranges from simple gathering and stocking of wild seeds for several clam species to sophisticated hatchery and growout operations for abalone and pearl oysters. The rapid development of intensive mariculture during the past decade may have exceeded the carrying capacity of some areas and contributed to deterioration of the culture environment. Abalone and scallop cultures in the north have been seriously affected by diseases and mortalities in recent years.
The eastern oyster (Crassostrea virginica) remains at historically low levels throughout the Chesapeake Bay. Recent efforts to restore oysters in the bay have focused on establishing a series of sanctuaries, or no-take zones, to increase oyster broodstock in selected tributaries. Oyster parasites continue to affect the rate of recovery in these tributaries; however, innovative management strategies, advances in aquaculture technology, and the availability of disease-tolerant broodstock from the lower Chesapeake Bay are providing ways to involve the public directly in restoration of this resource. A 1996 management decision to transplant large wild-caught oysters onto an oyster broodstock sanctuary reef in the Great Wicomico River, Virginia, was followed by greatly increased abundance of juvenile oysters throughout that river in 1997. Using that result as a model for strategic oyster reef restoration, citizens and school students have been enlisted to grow large numbers of hatchery-produced native oysters for restocking other sanctuary reefs throughout Chesapeake Bay. Efforts to supplement natural oyster populations in Hampton Roads, Virginia, began in May 1998, with the transplanting of 65,000 hatchery-produced oysters grown by school students. The oysters were transplanted onto strategically located sanctuary reefs constructed in the Lynnhaven and Elizabeth rivers. Surveys of these reefs following the oysters' spawning season have revealed order-of-magnitude increases in the abundance of juvenile oysters on both reefs, and correspondingly high spat settlement rates on oyster grounds surrounding the reefs. These results demonstrate that stocking strategically located broodstock reefs with hatchery-produced oysters grown by citizens can be an effective strategy for oyster restoration in the Chesapeake Bay.
Oyster cultch was added to the lower intertidal fringe of three created Spartina alterniflora marshes to examine its value in protecting the marsh from erosion. Twelve 5-m-wide plots were established at each site, with six randomly selected plots unaltered (noncultched) and cultch added to the remaining (cultched) plots. Within each cultched plot, cultch was placed along the low tide fringe of the marsh during July 1992, in a band 1.5 m wide by 0.25 m deep. Marsh-edge vegetation stability and sediment erosion were measured for each plot from September 1992 to April 1994. Significant differences (p < 0.05) in marsh-edge vegetation change were detected at the only south-facing site after a major southwester storm. Significantly different rates of sediment erosion and accretion also were observed at this same site. Areas upland of the marsh edge in the cultched areas showed an average accretion of 6.3 cm, while noncultched treatment areas showed an average loss of 3.2 cm. A second site, with a northern orientation, also experienced differential sediment accretion and erosion between treatment type, caused instead by boat wakes that were magnified by the abutment of a dredge effluent pipe across the entire front fringe of the site. During this period we observed significant differences in sediment accumulation, with the areas upland of the marsh edge in the cultched treatment having an average accretion of 2.9 cm and the noncultched an average loss of 1.3 cm.
Suspension-feeding bivalves serve to couple pelagic and benthic processes because they filter suspended particles from the water column and the undigested remains, ejected as mucus-bound feces and pseudofeces, sink to the sediment surface. This biodeposition can be extremely important in regulating water column processes where bivalves are abundant in coastal waters and in seasons when water temperatures are warm enough to promote active feeding. Bivalves under these conditions can exert "top-down" grazer control on phytoplankton and in the process reduce turbidity, thereby increasing the amount of light reaching the sediment surface. This has the effect of reducing the dominance of phytoplankton production and extending the depth to which ecologically important benthic plants, such as seagrasses and benthic microalgae, can grow. Nitrogen and phosphorus, excreted by the bivalves and regenerated from their biodeposits, are recycled back to the water column and support further phytoplankton production. In some situations, however, bivalves can also exert "bottom-up" nutrient control on phytoplankton production by changing nutrient regeneration processes within the sediment. Some of the N and P that was originally incorporated in phytoplankton, but was not digested by the bivalves, can become buried in the accumulating sediments. Where biodeposits are incorporated in aerobic surficial sediments that overlay deeper anaerobic sediments, microbially mediated, coupled nitrification- denitrification can permanently remove N from the sediments as N2 gas. Consequently, natural and aquaculture-reared stocks of bivalves are potentially a useful supplement to watershed management activities intended to reduce phytoplankton production by curbing anthropogenic N and P inputs to eutrophied aquatic systems. Environmental conditions at bivalve aquaculture sites should be carefully monitored, however, because biodeposition at very high bivalve densities may be so intense that the resulting microbial respiration reduces the oxygen content of the surrounding sediments. Reduction in sediment oxygen content can inhibit coupled nitrification-denitrification, cause P to become unbound and released to the water column, and the resulting buildup of H2S can be toxic to the benthos.
A large-scale field experiment was conducted to test whether the physical structure of biogenic reef habitat controls physical conditions (hydrodynamics and hydrographics) with subsequent influence on the performance (recruitment, growth, and survival) of a benthic suspension feeder. The experimental system consisted of restored subtidal oyster reefs inhabited by the eastern oyster Crassostrea virginica. To determine whether the size of reefs influences the flow environment and oyster performance, reefs of four heights-tall (2 m), short (1 m), dredged (0.6 m), and low (0.1 m)-were constructed at 3-m water depth in the Neuse River estuary, North Carolina, USA. To test whether oyster performance varies with water depth and hydrographic conditions, tall and short reefs were also constructed at 6-m water depth. Flow speed, sedimentation, temperature, salinity, dissolved oxygen, and the performance of oysters were measured as a function of reef height, position on reef, and water depth over a 10-mo period. Flow speed was found to increase on reefs with reef height and elevation on reefs. Rates of sediment deposition were seasonally highest where flow speed was lowest, at the bases of reefs, and seasonally decreased with increasing water depth. More than 90% of the surface area of low reefs was buried after only 16 mo of exposure in the estuary, indicating that reef height controls habitat quality (and quantity) indirectly through its effect on flow. Short reefs and the bases of tall reefs at 6-m depth were exposed to a total of 26 d of hypoxia/anoxia. No other reef treatment was exposed to >5 d of hypoxia. Physical conditions on experimental reefs had a profound influence on the performance of oysters as the flow environment alone explained 81% of variability in oyster growth and mortality. Recruitment of oysters over a 2-mo period was slightly higher on the front bases than the crests of reefs, but did not vary with reef height or water depth. After 10 mo, the shell growth and condition index of genetically similar, hatchery-raised oysters were greatest on the crests of tall and short reefs, where flow speed and quality of suspended food material were highest, and sediment deposition was lowest. Growth was greatest overall at the crests of tall reefs located at 6-m water depth where flow speed was high, and the numbers of days exposed to hypoxia/anoxia and variation in salinity were lowest. Total percentage mortality of oysters after 10 mo was greater on low reefs located at 3-m depth than on all other reef types and was greater on the bases than crests of tall, short, and dredged reefs. Predation by crabs and fishes accounted for 4-20% of total oyster mortality and showed no pattern across reef treatments. Results of this experiment indicate (1) that the physical structure and location of biogenic habitat controls local physical variables and (2) that, in turn, physical variables, especially flow speed, have a profound influence on the performance of a resident species. Realization that an ecological function of habitat is to indirectly control local population production through physical-biological coupling should improve our ability to conserve, restore, and manage habitat and associated species diversity. Better ecological engineering of restored oyster reef habitat is likely to improve fishery production and help maintain estuarine biodiversity.