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Marine invertebrates, such as oysters, were once thought to form large, panmictic populations with little genetic differentiation due to their high reproductive capacity and dual life stages. However, recent studies have shown significant genetic structuring and moderate gene flow across populations, influenced by factors like ocean currents, historical climate events, and environmental changes. The black-lip oyster ( Saccostrea echinata ), with its extensive dispersal potential, is ideal for population genetics studies. In current study, mitochondrial DNA (COI gene) was utilized to investigate the population structure, genetic diversity, and demographic history of S. echinata in the northern South China Sea (NSCS) and Beibu Gulf. Results revealed high genetic diversity with 82 haplotypes from 190 specimens, a star-shaped haplotype network, and significant genetic differentiation, with most variation occurring within populations. Genetic analysis identified three distinct genetic groups across the sampled regions. Historical demographic analysis indicated population expansion approximately 44–155 Kya after the Last Glacial Maximum. Genetic structure was shaped by historical climatic events causing isolation and secondary contact, as well as contemporary ocean currents influencing gene flow. The study highlights the complex interplay of genetic diversity, population structure, and historical dynamics in S. echinata , with implications for conservation and aquaculture in the Asia-Pacific region.

Cultivation of the tropical Blacklip Rock Oyster (BRO) ( Saccostrea spathulata ) is an emerging Indigenous-led aquaculture industry in the seasonal tropics of northern Australia. However, little is currently known about the potential for pathogen outbreaks in this species. We conducted a year-long study to establish a microbial baseline to identify potential oyster and human health risks to inform future food safety decision making in this nascent industry. In healthy oysters, we identified both the core microbiome of this oyster species and the presence of potential oyster and human pathogens. The core bacteriome comprised nine bacterial families, while the core vibriome comprised the animal pathogens Vibrio harveyi and V. owensii . The potential human pathogen V. parahaemolyticus was detected in some oysters during the wet season, during periods of increased rainfall, turbidity and total nitrogen. The bacteriome and vibriome of oysters were significantly different to the adjacent seawater and therefore we concluded that seawater is not an appropriate surrogate for pathogen risk surveillance in this developing industry. These results provide new knowledge on the microbiology of a previously understudied oyster species and will inform monitoring methods, harvesting and shellfish quality compliance in this emerging Indigenous-led industry.

We review the status of marine shellfish ecosystems formed primarily by bivalves in Australia, including: identifying ecosystem-forming species, assessing their historical and current extent, causes for decline and past and present management. Fourteen species of bivalves were identified as developing complex, three-dimensional reef or bed ecosystems in intertidal and subtidal areas across tropical, subtropical and temperate Australia. A dramatic decline in the extent and condition of Australia's two most common shellfish ecosystems, developed by Saccostrea glomerata and Ostrea angasi oysters, occurred during the mid-1800s to early 1900s in concurrence with extensive harvesting for food and lime production, ecosystem modification, disease outbreaks and a decline in water quality. Out of 118 historical locations containing O. angasi-developed ecosystems, only one location still contains the ecosystem whilst only six locations are known to still contain S. glomerata-developed ecosystems out of 60 historical locations. Ecosystems developed by the introduced oyster Crasostrea gigas are likely to be increasing in extent, whilst data on the remaining 11 ecosystem-forming species are limited, preventing a detailed assessment of their current ecosystem-forming status. Our analysis identifies that current knowledge on extent, physical characteristics, biodiversity and ecosystem services of Australian shellfish ecosystems is extremely limited. Despite the limited information on shellfish ecosystems, a number of restoration projects have recently been initiated across Australia and we propose a number of existing government policies and conservation mechanisms, if enacted, would readily serve to support the future conservation and recovery of Australia's shellfish ecosystems.

The mangrove oyster Saccostrea palmula is a relatively small but emerging species in aquaculture, and it is necessary to resume and increase studies on its cultivation. Therefore, we carried out a study that includes three main components for developing S. palmula culture in the Mexican Central Pacific: spat collection, pre-growth phase (eight weeks), and grow-out phase (six months). We tested natural (shell strings) and artificial (coupelles) collectors placed in contrasting environmental conditions: marine (La Boquita) and estuarine (Cuyutlan). The spat was pre-grown in suspended Australian trays at the two collection sites and under in-land pond conditions. Then, it was pooled under an estuarine environment and in a single lot for the final culture phase in Juluapan lagoon (all sites in Colima, Mexico). Spat collection was higher in coupelles (858.3 ± 175.6 spat coupelle-1) than in shell strings. The number of spat collected (13,062 spat), final pre-growth size (26.5 ± 0.6 mm shell height), and pre-growth survival (94.7%) were higher in La Boquita (marine environment). The final culture phase in Juluapan (estuarine conditions) was successful, recording an average height of 54.2 ± 4.9 mm and average total weight of 30.8 ± 6.9 g after six months of culture, after spat collection and pre-growth periods. We found the largest oyster, S. palmula, ever recorded (shell height 83.3 mm and total weight 59.4 g), and we confirmed that S. palmula has potential for artisanal aquaculture and socioeconomic regional development in the Mexican Central Pacific.

Ocean acidification (OA) is predicted to have widespread implications for marine organisms, yet the capacity for species to acclimate or adapt over this century remains unknown. Recent transgenerational studies have shown that for some marine species, exposure of adults to OA can facilitate positive carryover effects to their larval and juvenile offspring that help them to survive in acidifying oceanic conditions. But whether these positive carryover effects can persist into adulthood or the next generation is unknown. Here we tested whether positive carryover effects found in larvae of the oyster, Saccostrea glomerata following transgenerational exposure to elevated CO2, could persist into adulthood and whether subsequent transgenerational exposure of adults to elevated CO2 would facilitate similar adaptive responses in the next generation of larvae and juveniles. Following our previous transgenerational exposure of parental adults and first generation (F1) larvae to ambient (385 μatm) and elevated (856 μatm) CO2, newly settled F1 juveniles were transferred to the field at ambient CO2 for 14 months, until they reached reproductive maturity. At this time, the F1 adults were returned to the laboratory and the previous transgenerational CO2 exposure was repeated to produce F2 offspring. We found that the capacity of adults to regulate extracellular pH at elevated CO2 was improved if they had a prior history of transgenerational exposure to elevated CO2. In addition, subsequent transgenerational exposure of these adults led to an increase in the resilience of their larval and juvenile offspring. Offspring with a history of transgenerational exposure to elevated CO2 had a lower percentage abnormality, faster development rate, faster shell growth and increased heart rate at elevated CO2 compared with F2 offspring with no prior history of exposure to elevated CO2. Our results suggest that positive carryover effects originating during parental and larval exposure will be important in mediating some of the impacts of OA for later life-history stages and generations.

Ammonium (NH4+) plays a crucial role in the reproductive processes of key biotic groups in aquatic ecosystems—bivalves. This study aims to elucidate the effects of three different ammonium ion concentrations on sperm vitality, swimming kinematics, and morphology of Mimachlamys nobilis, Pinctada fucata martensii, and Saccostrea mordax. The results indicate that the sperm vitality and motility rates of M.nobilis and S. mordax are inversely proportional to the ammonium concentration, especially in the treatment group with an ammonium concentration of 3 mmol/L, where the decrease in sperm vitality and motility is most significant. In contrast, the sperm of P. fucata martensii reacted differently to increasing ammonium concentrations. After the addition of 2 mmol/L of ammonium, the sperm vitality and motility of P. fucata martensii reached a peak, showing a significant stimulatory effect. Additionally, as the ammonium concentration increased, the curling of the sperm flagella in M.nobilis and S. mordax increased. However, sperm flagella curling in P. fucata martensii showed no change compared to the control group. This study provides insights into the effects of ammonium concentrations on the sperm vitality and motility of three marine bivalve species and highlights the importance of sperm flagella curling as a factor affecting sperm.

The Mediterranean Sea is home to over 2/3 of the world’s charter boat traffic and hosts an estimated 1.5 million recreational boats. Studies elsewhere have demonstrated marinas as important hubs for the stepping-stone transfer of non-indigenous species (NIS), but these unique anthropogenic, and typically artificial habitats have largely gone overlooked in the Mediterranean as sources of NIS hot-spots. From April 2015 to November 2016, 34 marinas were sampled across the following Mediterranean countries: Spain, France, Italy, Malta, Greece, Turkey and Cyprus to investigate the NIS presence and richness in the specialized hard substrate material of these marina habitats. All macroinvertebrate taxa were collected and identified. Additionally, fouling samples were collected from approximately 600 boat-hulls from 25 of these marinas to determine if boats host diverse NIS not present in the marina. Here, we present data revealing that Mediterranean marinas indeed act as major hubs for the transfer of marine NIS, and we also provide evidence that recreational boats act as effective vectors of spread. From this wide-ranging geographical study, we report here numerous new NIS records at the basin, subregional, country and locality level. At the basin level, we report three NIS new to the Mediterranean Sea (Achelia sawayai sensu lato, Aorides longimerus, Cymodoce aff. fuscina), and the re-appearance of two NIS previously known but currently considered extinct in the Mediterranean (Bemlos leptocheirus, Saccostrea glomerata). We also compellingly update the distributions of many NIS in the Mediterranean Sea showing some recent spreading; we provide details for 11 new subregional records for NIS (Watersipora arcuata, Hydroides brachyacantha sensu lato and Saccostrea glomerata now present in the Western Mediterranean; Symplegma brakenhielmi, Stenothoe georgiana, Spirobranchus tertaceros sensu lato, Dendostrea folium sensu lato and Parasmittina egyptiaca now present in the Central Mediterranean, and W. arcuata, Bemlos leptocheirus and Dyspanopeus sayi in the Eastern Mediterranean). We also report 51 new NIS country records from recreational marinas: 12 for Malta, 10 for Cyprus, nine for Greece, six for Spain and France, five for Turkey and three for Italy, representing 32 species. Finally, we report 20 new NIS records (representing 17 species) found on recreational boat-hulls (mobile habitats), not yet found in the same marina, or in most cases, even the country. For each new NIS record, their native origin and global and Mediterranean distributions are provided, along with details of the new record. Additionally, taxonomic characters used for identification and photos of the specimens are also provided. These new NIS records should now be added to the relevant NIS databases compiled by several entities. Records of uncertain identity are also discussed, to assess the probability of valid non-indigenous status.

The taxonomy of the genus Saccostrea is very confused, however, there is relatively little molecular information available on Saccostrea. In this study, we determined and described for the first time the complete mitochondrial genome of Saccostrea malabonensis. The complete mitogenome of S. malabonensis is 16,204 bp in length, containing 12 protein-coding genes (lack of atp8 gene), two rRNA genes, 23 tRNA genes. The overall nucleotide composition of S. malabonensis has an AT content of 61.94% (26.29% A, 15.71% C, 22.35% G, 35.65% T). Phylogenetic analyses showed that S. malabonensis is first clustered with S. cucullata then united with Saccostrea kegaki.

Poor larval survival is a bottleneck to commercial hatchery production of the tropical black-lip rock oyster, Saccostrea echinata. This study investigated the synergistic effects of water temperature and salinity on embryonic and larval development across each major larval life stage. Results showed that water temperature and salinity have a significant effect on embryonic development of S. echinata and that embryos did not develop below 17 °C and 14 psu. Survival was high (55–100%) across all treatments and larval stages, and shell size was used primarily to determine larval response to treatments. Larval shell size increased as water temperature and salinity increased, reaching optima at 32 °C and 23 psu for D-veligers (mean DVM 78.18± 0.85 μm), at 32 °C and 26 psu for umbonate larvae (mean DVM 183.40± 2.60 μm), and at 32 °C and 29 psu for eyed larvae (mean DVM 249.64± 3.22 μm). It is recommended that S. echinata embryos and larvae are cultured within 28–32 °C and at salinity optima for each larval stage: embryo development at 32 psu, D-veligers and umbonate larvae between 23 and 26 psu, and eyed larvae between 28 and 30 psu. This is the first investigation of the combined effects of water temperature and salinity on S. echinata and provides valuable information to accelerate commercial aquaculture of this tropical species.

Whether sex determination of marine organisms can be altered by ocean acidification and warming during this century remains a significant, unanswered question. Here, we show that exposure of the protandric hermaphrodite oyster, Saccostrea glomerata to ocean acidification, but not warming, alters sex determination resulting in changes in sex ratios. After just one reproductive cycle there were 16% more females than males. The rate of gametogenesis, gonad area, fecundity, shell length, extracellular pH and survival decreased in response to ocean acidification. Warming as a sole stressor slightly increased the rate of gametogenesis, gonad area and fecundity, but this increase was masked by the impact of ocean acidification at a level predicted for this century. Alterations to sex determination, sex ratios and reproductive capacity will have flow on effects to reduce larval supply and population size of oysters and potentially other marine organisms.