Chapter

Climate Change and Bivalve Mass Mortality in Temperate Regions

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

One of the fastest-growing global food sectors is the bivalve aquaculture industry. Bivalves particularly oysters, mussels and clams are important sources of animal protein (Tan and Ransangan 2016a, b). Bivalve aquaculture represents 14–16% of the average per capita animal protein for 1.5 billion people and supports over 200,000 livelihoods, mostly in developing countries (FAO 2018). Most of the bivalves produced around the world (89%) are from aquaculture (FAO 2016). To date, mollusc aquaculture have accounted for 21.42% (17.14 million tonnes) of the total aquaculture production, with Asia being the largest contributor (92.27%) (FAO 2018).

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Environmental change increases physiological stress in bivalves in a number of ways, leaving them susceptible to pathogens. Warming water can enhance microbial growth, thereby increasing the content of organic matter in the water, with the subsequent microbial decomposition reducing dissolved oxygen levels (Soon and Zheng, 2019). Hypoxic conditions can impact bivalve immune systems and interact with diseases, for example rendering bivalve hosts less efficient at eliminating bacterial cells (Macey et al., 2008). ...
... For oysters in particular, blooms of this dinoflagellate were found to alter immune system competence in juveniles, thereby comprising their disease resistance. In addition to low dissolved oxygen levels and HABs, toxins and pollutants have been shown to promote infection by the bacterium Vibrio splendidus, the pathogen responsible for juvenile summer mortality in C. gigas spat, also known as bacillary necrosis disease (Soon and Zheng, 2019). ...
... The impacts of climate change on parasite transmission in the marine environment is in the early stages of our understanding (Burge et al., 2014). However, marine invertebrates demonstrate strong links between disease and climate (Marcogliese, 2008) and there is increasing evidence that climate change will affect the ecology of infectious diseases and the physiology of bivalve species and their resistance to infection (Soon and Zheng, 2019). Climate change could affect parasites by influencing the distribution and life-history of hosts (Callaway et al., 2012) and potentially increase host susceptibility to infection due to thermal stress (Harvell et al., 2002). ...
Article
Full-text available
Although research into the ecology and impacts of invasive species is prevalent, there are knowledge gaps relating to the role of invasive species in parasite transmission. This work synthesises invasive host–parasite interactions and impacts, using marine bivalves as a model group, to consider how global movement of shellfish consignments for aquaculture purposes facilitates the unintentional transfer of invasives. We discuss how invasive species can act as both hosts or parasitic organisms themselves, and introductions may lead to diseases within the bivalve aquaculture sector. This review highlights the importance of interdisciplinary research, with particular regard to the fields of parasitology and invasion ecology. We suggest that further integrating these fields will enhance critical knowledge of marine diseases, parasite-invasive-bivalve interplay dynamics, and potential mitigation strategies, including temperature-based disease surveillance models. We also address how climate change might impact invasive species, again with a focus on marine bivalves, and the potential outcomes for parasite transmission, including changes in host/parasite distribution, life-history and virulence. We acknowledge the importance of horizon scanning for future invasive host–parasite introductions and note that increased screening of invasive species, both in their native and invaded ranges, will provide clarity on invasion dynamics and potential impacts.
... At the same time, the increase in atmospheric CO 2 has caused dissolution of 550 billion tons of atmospheric CO 2 in global oceans, resulting in an increase of ocean acidity (pH is reduced from 8.2 to 8.1) in a process known as ocean acidification (OA) (Fig. 1) (Sabine et al. 2011;Feely et al., 2009). It is predicted that by the end of the 21st century, the pH of the ocean will decrease by 0.32 units (Queiros et al., 2015), as a result, OA is considered to be one of the greatest threats to marine ecosystems in the near future Repeated episodes of bivalve massive mortalities (Tan and Zheng, 2019;Tan and Ransangan, 2019;Tan and Ransangan, 2016c;McFarland et al., 2016), deadly bivalve disease outbreaks (Asplund et al., 2014;Williams et al., 2014), growth and development retardations (Watson et al., 2009), bivalve shell dissolutions (Yang et al., 2017;Waldbusser et al., 2010) and bivalve byssus strength reductions O'Donnell et al., 2013), which involved all life stages of bivalve from larvae to juvenile and adults, have been reported worldwide. It is clear from the literature that the ocean warming and ocean acidification are the two main drivers of anthropogenic climate change and have deleterious effects on marine biological processes. ...
... In general, ocean warming has received a lot of attention in the aquaculture sector, but acidification has received relatively less attention. Recently, the effects of seawater warming on bivalve aquaculture have been reviewed by Tan and Zheng (2019). On the other hand, for OA, although there are many time series observations and climate stimulation experiments on the effects of OA on bivalves, the information is not organized. ...
... As a result, the weakened immunity of bivalves in future climate scenarios may be beneficial for invading bacteria in infecting hosts. In addition, in high densities bivalve farms, bivalves are more vulnerable to OA due to bacteria can easily spread (Tan and Zheng, 2019). ...
... Shellfish aquaculture (defined here as culture of bivalves and mollusks), and the facility operators and broader community that it engages, is one example of a coastal system impacted by climate stress. Shellfish are sensitive to changes in environmental conditions such as temperature (Gagnaire et al., 2006;Le Deuff et al., 1996;Martinez et al., 2018;Vilchis et al., 2005), carbonate chemistry (Kroeker et al., 2013), and numerous other factors such as nutrients, disease, and sediment (Soon and Zheng, 2020). In particular, the ongoing global reduction in ocean pH, termed OA, is negatively impacting shellfish through decreased growth and survival (Hauri et al., 2009;Kroeker et al., 2013). ...
... The need to better understand drivers of shellfish health and mortality was mentioned in all but one of the interviews (Fig. 3). Mortality events can be severe, and periodically lead to loss of the majority of shellfish in some lease areas or hatcheries (Gray et al., 2022;King et al., 2021;Soon and Zheng, 2020). In some cases, growers estimated mortality of 90% of their in-bay oysters, and published literature about West Coast hatcheries cites events leading to mortality of over 75% of larvae, causing considerable economic damage (Barton et al., 2015;Mabardy et al., 2015). ...
... Scientific literature about the causes of such mortality events along the West Coast is sparse, but recent research points towards marine pathogens, harmful algae, warm water, and other interacting environmental factors as likely drivers of in-bay mortality events (Bill et al., 2016;Green et al., 2019;King et al., 2021), with low pH as an additional noteworthy stressor for land-based hatcheries (Barton et al., 2015). High uncertainty remains though around the mechanisms by which these factors lead to mortality events (Go et al., 2017;Gray et al., 2022) and how impacts and outcomes may vary by species (Soon and Zheng, 2020). In response to mortality caused by disease, warm water, OA, and broad environmental change, many growers mentioned development of genetically resistant shellfish strains as an avenue to improve adaptive capacity (e.g., Nascimento-Schulze et al., 2021), with comments similar to one grower's sentiments of hoping to "breed animals that can adapt to changing conditions. ...
Article
Full-text available
Coastal communities along the U.S. West Coast experience a myriad of environmental stressors, including exposure to low pH waters exacerbated by ocean acidification (OA). This can result in ecological and social consequences, making necessary the exploration and support for locally relevant strategies to adapt to OA and other environmental changes. The shellfish aquaculture industry along the West Coast is particularly vulnerable to OA, given the negative effects of low pH on shellfish survival and growth. As such, the social-ecological system exemplified by this industry serves as an opportunity to identify and address strategies for local adaptation. Through interviews conducted with West Coast shellfish farm owners and managers (‘growers’), we investigate perceptions of OA and environmental change and identify specific strategies for adaptation. We find that growers are concerned about OA, among many other environmental stressors such as marine pathogens and water temperature. However, growers are often unable to attribute changes in shellfish survival or health to these environmental factors due to a lack of data and the resources and network required to acquire and interpret these data. From these interviews, we identify a list of adaptive strategies growers employ or would like to employ to improve their overall adaptive capacity to multiple stressors (environmental, economic, political), which together, allow farms to weather periods of OA-induced stress more effectively. Very few studies to date have identified specific adaptive strategies derived directly from the communities being impacted. This work therefore fills a gap in the literature on adaptive capacity by amplifying the voices of those on the front lines of climate change and identifying explicit pathways for adaptation.
... In recent years, with the development of the oyster industry summer mortality has been one of the most severe questions in farming practice. Previous studies indicated that the two major reasons for bivalve mass mortality were temperature increasing and dissolved oxygen decreasing (Parthasarathy et al., 1992;Joos et al., 2003;Soon and Zheng, 2019;Zhao et al., 2019;He et al., 2021), and hypoxia is considered to be one of the key factors affecting the survival of ocean organisms (Gu et al., 2019;Andreyeva et al., 2021). Benthic intertidal communities have developed appropriate survival mechanisms due to daily exposure into the air during low tide (Larade and Storey, 2002;Zhao et al., 2020), but over-farming, sediment covering, or algae blooming (Wu, 2002) could also cause water hypoxia. ...
Article
Full-text available
Hypoxia is considered to be one of the key factors affecting the survival of ocean organisms, it is necessary to parse the molecular processes involved in response to hypoxia. As a potential breeding species, the hybrid of Crassostrea sikamea (♀) × Crassostrea gigas (♂) shows valuable heterosis in survival and growth traits. Thus, RNA de novo was deployed in this study to analyze the molecular processes in the hybrids under hypoxia stress. The hybrids were cultured in occluded water, then the dissolved oxygen was gradually consumed by oysters, and the gill tissue of hybrids was sampled at the very beginning and the lowest respiration point in the experiment. In the current study, 901 significant differentially expressed genes (DEGs) were identified under hypoxia compared to normoxia, among which 432 DEGs were downregulated, and the other 469 DEGs were upregulated. A total of 27 GO terms were significantly enriched, such as an integral component of membrane, extracellular region, immune response, tumor necrosis factor receptor binding, and neurotransmitter: sodium symporter activity. Besides, 19 KEGG pathways were significantly enriched, such as apoptosis, Th1 and Th2 cell differentiation, complement, and coagulation cascades, antigen processing and presentation, notch signaling pathway, and cytokine–cytokine receptor interaction. The current results showed that the TRAIL genes were downregulated, but the HSP70 and LIGHT genes were upregulated, which indicated the inhibition of Apoptosis, and the activity of innate immunity in oysters under hypoxia. This study provides preliminary insight into the molecular response to hypoxia in the gill of hybrids.
... The long-term persistence of biodiversity is of increasing concern under changing environmental conditions. The threat of disease outbreaks and climate change have been identified as major risks to bivalve populations (Tan et al. 2020;Tan and Zheng 2019). These threats are likely to have synergistic consequences, with susceptibility to disease outbreaks amplified by the stress of the changing environmental conditions (Butt and Raftos 2007;Goncalves et al. 2017;Guo and Ford 2016;Leung and Bates 2013;Mackenzie et al. 2014). ...
Article
Full-text available
Oyster reef habitats are critical to coastal biodiversity and their decline has prompted restoration efforts in Australia. Knowledge gaps exist regarding the population structure and diversity of key species in these habitats. This may be critical information for the design of effective restoration programs. Sydney rock oysters (Saccostrea glomerata) are the dominant reef-forming bivalve in eastern Australia. Wild populations of S. glomerata have declined due to overharvesting, disease outbreaks, coastal development and reduced water quality. Here, we use genetic markers identified by genome-wide sequencing to investigate the genetic structure and diversity of wild Sydney rock oysters throughout their distribution in eastern Australia. We examine evidence for past population bottlenecks and spatial genetic structure associated with the East Australian Current. Analysis of 3, 400 neutral single-nucleotide polymorphisms (SNPs) revealed a single population, and an overlap with two other Saccostrea sp. at the northernmost boundary of the distribution. We detected signals of asymmetric gene flow consistent with the direction of the East Australian Current, and spatial structure patterns of limited genetic isolation by distance and spatial autocorrelation in the northern region (which experiences stronger effects of the East Australian Current) but not in the southern region of the distribution. We found no evidence of significant recent bottlenecks, with high effective population size throughout the species’ range. This information will provide a baseline against which to assess the impact of restoration projects, and guide strategies for sourcing stock for the enhancement of wild oyster populations. Our results provide a positive outlook for the resilience and adaptive capacity of Sydney rock oysters, and highlight wild populations as valuable resources for aquaculture and restoration initiatives.
... In recent years, cultured scallops have decreased their growth rates and experienced massive mortalities of unknown origin. Although there are many factors that could cause scallop mass mortality (Soon and Zheng, 2020), pathogenic infections cannot be ruled out. The mortality of A. purpuratus larvae has been associated with the presence of the Gram-negative bacteria Vibrio splendidus (Rojas et al., 2015). ...
Article
Full-text available
The scallop Argopecten purpuratus is a species of importance for aquaculture in Chile and Peru, but in recent years, they have decreased their growth rates and experienced massive mortalities potentially associated with pathogenic infections. Characterization of proteins involved in the immunity status of A. purpuratus is of interest to develop molecular markers to support its culture. Here we report the characterization of a new Peroxiredoxin (Prx) homologue, the first one identified in A. purpuratus. Prxs are a ubiquitous family of cysteine-dependent peroxidase enzymes that play a dominant role in the regulation of peroxide levels in cells, as rapidly detoxify peroxynitrite, hydrogen peroxide and organic hydroperoxides. The molecular and phylogenetic analyses of this gene showed that it is a new member of the PrxV family, thus, it was designated as ApPrxV. This gene showed to be constitutively expressed in each examined tissue, but at a higher level in the striated adductor muscle. ApPrxV expression was highly upregulated in haemocytes in response to an immune challenge with pathogen bacteria Vibrio splendidus. Overall results indicate that ApPrxV is a constitutive and inducible protein that can play an important role in the immune response of A. purpuratus against bacterial infection. Therefore, the results of this study can (i) provide the bases for future functional studies to assess the health status of A. purpuratus; and (ii) can guide the development of molecular markers for future selective breeding of this bivalve.
... These populations are also submitted to the strong variations that may have an impact on physiology of mussels, changing thus their global status. Temperature is also known to have a synergic effect together with contaminants (Cherkasov et al., 2010;Lannig et al., 2006;Soon and Zheng, 2019). Energy cost caused by natural fluctuations and exceptional events repetition might make organisms more vulnerable to anthropic pollution at long term and impact population dynamics. ...
Article
Aquatic organisms such as bivalves are particularly sensitive to seasonal fluctuations associated with climate changes. Energy metabolism management is also closely related to environmental fluctuations. Changes in both biotic and abiotic conditions, such as the reproduction status and temperature respectively, may affect the organism energy status. A bivalve sentinel species, Dreissena polymorpha was sampled along its one-year reproduction cycle in situ (2018–2019) to study natural modulations on several markers of energy metabolism regarding seasonal variations in situ. A panel of different processes involved in energy metabolism was monitored through different functions such as energy balance regulation, mitochondrial density, and aerobic/anaerobic metabolism. The typical schema expected was observed in a major part of measured responses. However, the monitored population of D. polymorpha showed signs of metabolism disturbances caused by an external stressor from April 2019. Targeting a major part of energy metabolism functions, a global analysis of responses suggested a putative impact on the mitochondrial respiratory chain due to potential pollution. This study highlighted also the particular relevance of in situ monitoring to investigate the impacts of environmental change on sentinel species.
... The ability of carotenoids in regulating the transcription of various PRR genes has been extensively studied in vertebrates, particularly in humans (24,25). Moreover, the immune response of invertebrates to infectious diseases has received considerable attention because many of them are important species in fisheries and aquaculture, while others are critical to the structure and function of ecosystems (26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39). ...
Article
Full-text available
Carotenoids are biologically active pigments that are well-known to enhance the defense and immunity of the vertebrate system. However, in invertebrates, the role of carotenoids in immunity is not clear. Therefore, this study aims to review the scientific evidence for the role of carotenoids in invertebrate immunization. From the analysis of published literatures and recent studies from our laboratory, it is obvious that carotenoids are involved in invertebrate immunity in two ways. On the one hand, carotenoids can act as antioxidant enzymes to remove singlet oxygen, superoxide anion radicals, and hydroxyl radicals, thereby reducing SOD activity and reducing the cost of immunity. In some organisms, carotenoids have been shown to promote SOD activity by up-regulating the expression of the ZnCuSOD gene. Carotenoids, on the other hand, play a role in the expression and regulation of many genes involved in invertebrate immunity, including thioredoxins (TRX), peptidoglycan recognition receptor proteins (PGRPs), ferritins, prophenoloxidase (ProPO), vitellogenin (Vg), toll-like receptor (TLRs), heat shock proteins (HSPs), and CuZnSOD gene. The information in this review is very useful for updating our understanding of the progress of carotenoid research in invertebrate immunology and to help identify topics for future topics.
... Heat commonly accompanied hypoxia , and high temperature has been shown to play a key role in controlling hypoxia (Cai et al., 2014). A previous review has shown that increasing seawater temperature and decreasing DO were two main reasons for bivalve mass mortality (Soon and Zheng, 2019). Unlike other swimming animals that can migrate to the poles or swim to deeper depths, shellfish larvae counterintuitively move to warmer water, which might result in their high mortality rates (Fuchs et al., 2020). ...
Article
With global changes and anthropogenic activities, heat and hypoxia have become frequent stressors in aquatic environments. However, the molecular defense mechanisms of aquatic organisms, especially bivalves, against the synergistic effects of heat and hypoxia have not been fully elucidated. In this study, we analyzed transcriptomic data of the gills of Mercenaria mercenaria, an economically and ecologically important bivalve, under several stress challenges: high temperature (heat), low dissolved oxygen (hypoxia), and heat plus hypoxia. GO and KEGG enrichment analyses were performed on the differentially expressed gene sets of heat-induced genes under various dissolved oxygen (DO) solubilities, hypoxia-induced genes under different (normal and high) temperatures and common heat plus hypoxia stress-induced genes. We found that protein-folding item were significantly enriched in common differentially expressed heat-induced genes comparisons, with a high expression of molecular chaperones HSP90 and TCP1. Moreover, microtubule-related GO terms were significantly enriched in differentially expressed hypoxia-induced genes under different temperatures, and kinesin and dynein-related genes were commonly upregulated in the hypoxia challenge groups. Protein processing in endoplasmic reticulum and ubiquitin-mediated proteolysis were the most significantly enriched pathways in common heat plus hypoxia stress-induced genes. Furthermore, correctly-folding related genes, luminal chaperones, and ER-associated degradation related genes were upregulated under heat plus hypoxia stresses. Altogether, our results provided new insights on understanding the molecular defense mechanisms against heat and hypoxia stress in hard clams.
... Adult P. canaliculus can survive a 3 h acute heat shock immersed at temperatures of up to 31 • C (Dunphy et al., 2015), and intertidal mussels from a selection of South Island sites exposed to a 6 h emersion heat shock, were found to have an LT50 of 32-33 • C (Sorte et al., 2018). Field studies and observations (Cotter et al., 2010;Soon and Zheng, 2020) and laboratory studies (Dimitriadis et al., 2012;Rahman et al., 2019;Velez et al., 2017) on other bivalves have found that exposure to seawater temperatures lower than the LT50 temperature of a species can be detrimental to health and survival. ...
Article
Marine farmers have reported increased incidence of mass mortalities of New Zealand green-lipped mussels, Perna canaliculus, grown on near-shore long-line aquaculture farms. While the causative agents remain unknown, die-off events typically occur during the warmest months of the austral summer and appear correlated to unprecedented summer marine heatwaves that have impacted the eastern Tasman Sea in recent years. To further elucidate the role of chronic heat stress as a predisposing factor to ‘summer mortality’, adult P. canaliculus were incubated at 17, 21 and 24 °C for 13 months. Overall biological performance was impacted in the elevated temperature treatments; mean mass gain (Specific Growth Rate) at 17 °C was 0.21% day⁻¹, but fell to 0.18% day⁻¹ at 21 °C and 0.16% day⁻¹ at 24 °C. A survival tipping point was apparent between 21 and 24 °C, with net mortality of 6 and 10% at 17 and 21 °C, respectively, declining to 100% at 24 °C. Sacrificial gill and haemolymph samples taken every 4–8 weeks showed little evidence of temperature perturbation upon either haemocyte function or the metabolomic profile during the first 4–6 months of incubation. Beyond 6 months, a steady increase in the proportion of haemocytes showing signs of respiratory burst (superoxide-positive) or apoptosis increased steadily at 24 °C, along with a substantial increase in the levels of amino acids frequently associated with anaerobiosis or antioxidant support. During this period, even the more benign temperature treatments of 17 and 21 °C showed increased haemocyte apoptosis and a metabolite profile consistent with increasing protein catabolism. Prolonged exposure to artificially stabilised ‘summer' temperatures therefore appears detrimental to P. canaliculus, with important implications for the operation of captive broodstock conditioning systems. While stable, elevated temperatures up to 24 °C are unlikely to fully account for current observations of summer mortality, disruptions to energy metabolism and immunocompetency are likely to increase the mussels' vulnerability to pathogens and other stressors. On-going research is required to assess the impacts of realistic, fluctuating temperatures, with consideration of the implications for potential pathogens.
... Marine bivalves are calcifying ecosystem engineers, which are important in ecosystem functioning and aquaculture (Cranford et al., 2012). In accordance with their ecological and commercial relevance, the interest in OA research on bivalves is growing steadily and has increased particularly in recent years (e.g., Berge et al., 2006;Cummings et al., 2011;Li et al., 2017;Zhao et al., 2017;Rastrick et al., 2018a;Tan and Zheng, 2019). Evidence from several previous studies suggests that elevated seawater pCO 2 affects calcification (e.g., Ries et al., 2009;Melzner et al., 2011), growth (e.g., Thomsen et al., 2010;Kroeker et al., 2013), burrowing behavior (e.g., Clements et al., 2015;Peng et al., 2017), energetics (e.g., Wang et al., 2015;Zhao et al., 2017;Rastrick et al., 2018a) and immune response (e.g., Bibby et al., 2008;Zha et al., 2017) in bivalves such as oysters, mussels, and clams. ...
Article
Full-text available
Ocean acidification (OA) caused by elevated atmospheric CO2 concentration is predicted to have negative impacts on marine bivalves in aquaculture. However, to date, most of our knowledge is derived from short-term laboratory-based experiments, which are difficult to scale to real-world production. Therefore, field experiments, such as this study, are critical for improving ecological relevance. Due to the ability of seaweed to absorb dissolved carbon dioxide from the surrounding seawater through photosynthesis, seaweed has gained theoretical attention as a potential partner of bivalves in integrated aquaculture to help mitigate the adverse effects of OA. Consequently, this study investigates the impact of elevated pCO2 on the physiological responses of the Pacific oyster Crassostrea gigas in the presence and absence of kelp (Saccharina japonica) using in situ mesocosms. For 30 days, mesocosms were exposed to six treatments, consisting of two pCO2 treatments (500 and 900 μatm) combined with three biotic treatments (oyster alone, kelp alone, and integrated kelp and oyster aquaculture). Results showed that the clearance rate (CR) and scope for growth (SfG) of C. gigas were significantly reduced by elevated pCO2, whereas respiration rates (MO2) and ammonium excretion rates (ER) were significantly increased. However, food absorption efficiency (AE) was not significantly affected by elevated pCO2. The presence of S. japonica changed the daytime pHNBS of experimental units by ~0.16 units in the elevated pCO2 treatment. As a consequence, CR and SfG significantly increased and MO2 and ER decreased compared to C. gigas exposed to elevated pCO2 without S. japonica. These findings indicate that the presence of S. japonica in integrated aquaculture may help shield C. gigas from the negative effects of elevated seawater pCO2.
... Frequent extreme weather leads high temperature is likely to cause the economic loss of shellfish industry (Avdelas et al., 2021). Several studies reported that mass mortality events of shellfish due to heat-induced mortality, such as organ fragility (shell and valves), organ oxidation damage, and immunesuppression (Mackenzie et al., 2014;Martinez et al., 2018;Soon and Zheng, 2019;Nguyen and Alfaro, 2020). ...
Article
E3 ubiquitin ligase (E3s) plays an important role in ubiquitin proteasome pathway, proteins containing homologous E6-AP carboxyl terminus (HECT) domains. However, the role of HECT E3 ubiquitin ligase in mollusk was rarely explored. In this study, we performed a genome-wide analysis of the HECT domain-containing gene in Ruditapes philippinarum to identify and predict the structural and functional characterization of HECT genes in response to abiotic and biotic stress. A total of sixteen members of HECT gene family were identified and analyzed for the gene structure, phylogenetic relation, three-dimensional structure, protein interaction network, and expression patterns. Experimental results demonstrated that Rph.HUWE1, Rph.HECTD1, Rph.Ubr5 were significantly up-regulated in response to heat stress and bacterial challenge. Taken together, our data provide insights into the potential function of HECT E3 ligase in heat stress and Vibrio anguillarum infection.
... The Manila clam, Ruditapes philippinarum, lives in the intertidal zone worldwide and is one of the most ecologically and economically important bivalves (Zhao et al., 2012). In this era of rapid climate change, heatwaves can have detrimental effects on clams at various levels of biological organization (Soon and Zheng, 2019). Research reports demonstrate that marine heatwaves profoundly affect marine organisms from 2003 to 2018 (Di Garrabou et al., 2009;Gentemann et al., 2017;Gao et al., 2020), especially their growth, development, and survival. ...
Article
Full-text available
Heatwaves are becoming hotter, longer and more frequent, threatening the survival of intertidal bivalves and devastating their ecosystems. Yet, substantially overlooked are heatwave-induced post-responses, which are important to assess cascading consequences. Here, we investigated responses of intertidal bivalves, Ruditapes philippinarum, to recurrent heatwaves. Physiological and gene expression analyses demonstrated that the mantle tissue of R. philippinarum did not sensitively respond to heatwaves, but revealed post-responses under recovery scenarios. Of 20 genes related to essential physiology and fitness, 18 were down-regulated during the 1st recovery period, but following repeated exposure, 13 genes were up-regulated, in line with significantly increased activities of energy-metabolizing enzymes, and antioxidant and nonspecific enzymes. The down-regulation of genes involved in biomineralization, nevertheless, was observed under recovery scenarios, implying the trade-off between essential physiological and fitness-related functions. These findings pave the way for understanding the physiological plasticity of marine bivalves in response to intensifying heatwaves.
... Manila clam (Ruditapes philippinarum) is one of the most economically important marine bivalves (Zhang et al. 2006) with a worldwide production of 4.2 million tons in 2017 (Jiang et al. 2020) which is equivalent to 6.7 million USD (FAO 2021). Summer and winter mortality due to rigorous environmental change such as extreme rainfall, drought, and thermal extremes has become the most serious problems in aquaculture industry (FAO 2019;Soon et al. 2019;Lan et al. 2018). In the past several decades, many studies have used Manila clam as an ecological indicator for investigating temperature tolerance-related issues at different levels of temperature challenges (Xu et al. 2015;Han et al. 2008;Zhang et al. 2020;Dong et al. 2018;Richard et al. 2015). ...
Article
Full-text available
The Manila clam (Ruditapes philippinarum) is one of the most important aquaculture species and widely distributed along the coasts of China, Japan, and Korea. Due to its wide distribution, it can tolerate a wide range of temperature. Studying the gene expression profiles of clam gills had found differentially expressed genes (DEGs) and pathway involved in temperature stress tolerance. A systematic study of cellular response to temperature stress may provide insights into the mechanism of acquired tolerance. Here, weighted gene co-expression network analysis (WGCNA) was carried out using RNA-seq data from gill transcriptome in response to high and low temperature stress. There are a total 32 gene modules, of which 18 gene modules were identified as temperature-related modules. Blue module was one significantly correlated with temperature which was associated with cellular metabolism, apoptosis pathway, ER stress, and others.
Article
The increasing global population poses a huge challenge to food security, especially in terms of providing adequate sustainable and affordable high quality lipids. This article reviews the sources of natural omega-3 LC-PUFA and identifies the future direction for producing high quality lipids to meet growing market demands. Generally, bivalve lipids are high quality source of lipids that are beneficial to human health, regardless of species and habitat. There is also reason to believe that the development of bivalve farming worldwide, selective breeding of bivalves to increase the accumulation of omega-3 LC-PUFA and practising efficient usage of bivalve lipids can meeting some, if not all, of the growing demand for omega-3 LC-PUFA. Such information will aid to establish a promising source of high quality natural omega-3 LC-PUFA and ensure that all consumers have access to sufficient omega-3 LC-PUFA at an affordable price to support a healthier and balanced diet.
Article
Noble scallop Chlamys nobilis is an important marine bivalve that has been extensively cultured in the south coast of China since the 1980s. Unfortunately, since the late 1990s, the farmed scallops often suffered from regional mass mortality, which results in enormous economic losses to farmers and industries. In 2017, another mass mortality event occurred in Nan'ao Island, Shantou, China. In this study, the cause of C. nobilis mass mortality in 2017 was first investigated in the field, and then validated in a laboratory experiment. In the field, three sampling sites were selected according to the scallop mortality rate: Hunter Bay (90% mortality), Baisha Bay (67% mortality) and Longhai (6% mortality). Meanwhile, environmental parameters (temperature, salinity, DO, pH and chlorophyll a) of each site were also measured in situ. Then, water and scallop samples were collected randomly for the analysis of phytoplankton diversity and algal toxin activity using 18S rDNA and PP2A inhibition assay, respectively. In laboratory, healthy scallops were challenged with Karenia mikimotoi (1 × 10³ cells/mL) for 30 h. The field results showed that no significant difference in those environmental parameters existed among the three sites, but the relative abundance of K. mikimotoi in seawater and scallops' intestines in Hunter Bay and Baisha Bay was significantly higher than that in Longhai, and sick scallops contained significantly higher algal toxin activity than healthy ones. Laboratory results revealed that challenged scallops with K. mikimotoi showed significantly higher mortality rate and algal toxin activity than healthy ones, and low density of K. mikimotoi (1 × 10³ cells/mL) was sufficient to cause >50% scallops' mortality within 26 h. This study provides the first evidence that low K. mikimotoi cell density can cause massive mortality in C. nobilis, and provides useful information as guide to prevent scallop mass mortality in the future.
Article
Noble scallop, an economically important edible marine bivalve displays polymorphism in shells (golden and brown) and flesh colors (orange and white). Mass mortality of noble scallops usually occurs during the winter months. Interestingly, carotenoid-rich golden scallops demonstrated much higher survival rates than brown scallops in winter. In order to understand the response of polymorphic noble scallops to sequential cold stress, the present study aimed to investigate the enzyme and non-enzymatic antioxidant responses of golden and brown scallops under sequential cold stress. Parameters evaluated included total carotenoid content (TCC), fatty acid composition, total antioxidant capacity (TAC), methylenedioxyamphetamine (MDA) content, catalase (CAT) activity, and superoxide dismutase (SOD) enzyme activity. The results of the present study revealed that golden scallops have higher cold tolerance than brown scallops. Golden and brown scallops are well adapted to low water temperature of above 12 °C, but in areas where winter water temperatures are below 12 °C, golden scallops are more suitable for aquaculture than brown scallops. The findings of this study are crucial to understanding the physiological responses of polymorphic scallops to cold stress and identify suitable candidates for winter aquaculture.
Article
The Nan'ao Golden Scallop discussed in this paper is a new breed of noble scallop, Chlamys nobilis, produced by four generations of genetic breeding selections and two generations of culture demonstrations. Performed for the first time at Shantou University, the genetic breeding program was motivated by the need to reduce vulnerability and improve the adaptive capacity of noble scallops to the dynamic environment. This paper reviews the scientific evidences on aquaculture advantages of Nan'ao Golden Scallop, and identifies gaps in knowledge that require further research. From the analysis of published data, it is obvious that Nan'ao Golden Scallop is more nutritious and less susceptible to stress than common brown scallops. The high TCC of Nan'ao Golden Scallop up-regulate the expression of various immune related genes under stressful conditions. Since molluscs do not possess specific immunity, the information in this paper is very useful for improving the aquaculture performance of molluscs by selective breeding techniques.
Article
The noble scallop Chlamys nobilis is an important edible marine bivalve that is widely cultivated in the sea of southern China. Unfortunately, the mass mortality of noble scallops frequently occurs during the winter months. The present study investigated the effects of acute cold stress (8 °C) to the physiological responses of polymorphic noble scallops, by assessing the HSP70 gene expression, total carotenoid content (TCC), total antioxidant capacity (TAC), malondialdehyde (MDA) content, catalase (CAT) activity and superoxide dismutase (SOD) enzymatic activity in different tissues of golden and brown scallops. The results of the present study revealed that MDA, TCC and CAT increased drastically in most tissues in the early stage of acute cold stress (0-3 h), but TCC, SOD and CAT generally showed a downward trend. Within 3-6 h of acute cold stress, MDA content decreased in most tissues and the SOD content increased significantly in most tissues, while TCC and CAT remained at peak. After 6 h of acute cold stress, MDA content continued to increase in most tissues, while TCC, CAT, SOD and TAC decreased or remained at a lower level. For HSP70 expression, up-regulation of the HSP70 gene was observed only in mantle of brown scallops and hemolymph of golden scallops at 3 h and 24 h, respectively. The findings of the present study can better understand the physiological response of noble scallops to acute cold stress.
Article
In the context of global climatic changes, marine organisms have been exposed to environmental stressors including heat and hypoxia. This calls for the design of multi-stressors to uncover the impact of oceanic factors on aquatic organisms. So far, little is known about the metabolic response of marine organisms, especially bivalves, to the combined effects of heat and hypoxia. In this study, we employed widely targeted metabolomic analysis to study the metabolic response of gills in hard clam, a heat- and hypoxia-tolerant bivalve. A total of 810 metabolites were identified. Results showed that the heat group (HT) and heat plus hypoxia group (HL) had a higher number of differential metabolites than the hypoxia group (LO). Glycolysis was affected by the heat and heat plus hypoxia stress. Moreover, anaerobic metabolic biomarkers were accumulated marking the onset of anaerobic metabolism. Environmental stresses may affect Tricarboxylic acid (TCA) cycle. Accumulation of carnitine and glycerophospholipid may promote fatty acid β oxidation and maintain cell membrane stability, respectively. The high content of oxidized lipids (i.e., Leukotriene) in HL and HT groups implies that the organisms were under ROS stress. The significantly differential metabolites of organic osmolytes and vitamins might relieve ROS stress. Moreover, accumulation of thermoprotective osmolytes (monosaccharide, Trimethylamine N-oxide (TMAO)) accumulation is helpful to maintain protein homeostasis. This investigation provides new insights into the adaptation mechanisms of hard clam to heat, hypoxia and combined stress at the metabolite level and highlights the roles of molecules and protectants.
Article
Mollusks are excellent dietary sources for LC-PUFA. However, the main challenge limiting mollusk production is the high mortality rate of molluskan larvae in early life cycle stages. This paper reviews scientific evidences on molecular and biochemical studies of LC-PUFA biosynthesis in commercially important molluskan species. It carefully summarizes the pertinent data published on specific research questions to improve the understanding of the diverse evidences. It is helpful to clarify the current state of research and determine topics for future studies on LC-PUFA biosynthesis in mollusks. From the analysis of published data, mollusks have the ability to biosynthesis LC-PUFA to a certain extent. LC-PUFA biosynthesis information of commercially important molluskan species can be useful to determine the fatty acids essential for their diet. Therefore, specific management strategies or feeds can be developed to strengthen the industry by improving the health and survival rate of molluskan larvae.
Article
Omega-3 Long-chain polyunsaturated fatty acids (n-3 LC-PUFA) are beneficial to human health. Since the industrial revolution, with the tremendous increase of human population, the supply of natural n-3 LC-PUFA is far lower than the nutritional need of n-3 LC-PUFA. Therefore, a new alternative source of natural n-3 LC-PUFA is urgently needed to reduce the supply and demand gap of n-3 LC-PUFA. Mollusks, mainly bivalves, are rich in n-3 LC-PUFA, but the information of bivalves' lipid profile is not well organized. Therefore, this study aims to analyze the published fatty acid profiles of bivalves and reveal the potential of bivalve aquaculture in meeting the nutritional needs of human for n-3 LC-PUFA. There are growing evidence show that the nutritional quality of bivalve lipid is not only species-specific, but also geographical specific. To date, bivalve aquaculture has not been evenly practiced across the globe. It can be seen that aquaculture is predominant in Asia, especially China. Unlike fish aquaculture, bivalve aquaculture does not rely on fishmeal and fish oil inputs, so it has better room for expansion. In order to unleash the full potential of bivalve aquaculture, there are some challenges need to be addressed, including recurrent mass mortalities of farmed bivalves, food safety and food security issues. The information of this article is very useful to provide an overview of lipid nutritional quality of bivalves, and reveal the potential of bivalve aquaculture in meeting the growing demand of human for n-3 LC-PUFA.
Article
Bivalves are carriers of toxins produced by harmful algal blooms (HAB) species and were initially thought to be relatively unaffected. However, in recent years, increasing evidence has shown that bivalves are not only carriers of toxins produced by HAB species, but that HAB species and their secreted toxins can also alter the behaviour, physiology and cellular responses of bivalves, and even lead to the mortality of bivalves in severe cases. In addition, exposure of bivalves to HAB species and their secreted toxins may also negatively affect bivalve immunity and resistance to environmental changes. Despite the available of many relevant reports, the information is poorly organized and the link between HABs and bivalve robustness to environmental stressors is unclear. Therefore, understanding the potential impact of HAB species and their secreted toxins on bivalve aquaculture is critical. Here, we conduced a comprehensive scientific review of the potential effects of HAB species and their secreted toxins on the physiology and immunity of bivalves and their robustness to environmental stress. In general, scientific evidence suggests that exposure of bivalves to HAB species and their secreted toxins can hamper the immune system of bivalves, depending on the HAB and bivalve species and the natural environment of bivalves. This information helps to elucidate the current state of research and to determine topics for future studies on the effects of harmful algae blooms on bivalves.
Article
In the recent years, marine heatwaves (MHWs) have caused devastating impacts on marine life. The understanding of the combined effects of these extreme events and anthropogenic pollution is a vital challenge. In particular, the combined effect of MHWs on the toxicity of pharmaceuticals to aquatic life remains unclear. To contribute to these issues, the main goal of the present investigation was to evaluate how MHWs may increase caffeine (CAF) toxicity on the clam Ruditapes philippinarum and the mussel Mytilus galloprovincialis. Bioaccumulation levels and changes on oxidative stress, metabolic capacity and neurotoxic status related biomarkers were investigated. The obtained results revealed the absence of CAF accumulation in both species. However, the used contaminant generated in both bivalves' species alteration on neurotransmission, detoxification mechanisms induction as well as cellular damage. The increase of antioxidant defence mechanisms was complemented by an increase of metabolic activity and decrease of energy reserves. The obtained results seemed magnified in presence of a simulated MHW, suggesting to a climate-induced toxicant sensitivities’ response. On this perspective, understanding of how toxicological mechanisms interact with climate-induced stressors will provide a solid platform to improve effect assessments for both humans and wildlife.
Article
Lysozymes are antimicrobial acid hydrolases widely distributed in nature. They are located inside the cells in lysosomes, or they are secreted to the extracellular space, where they can lyse the cell wall of certain species of bacteria via hydrolysis of the peptidoglycan. Thus, lysozymes are bacteriolytic enzymes and play a major biological role in biodefense, as these enzymes can act as antibacterial and immune-modulating agents. In this study, we characterized a g-type lysozyme from the scallop Argopecten purpuratus named ApGlys. The cDNA sequence comprises an open reading frame (ORF) of 600 nucleotides, codifying for a putative protein of 200 amino acids with a signal peptide of 18 amino acids. The deduced mature protein sequence displays a molecular weight of 20.07 kDa and an isoelectric point (pI) of 6.49. ApGlys deduced protein sequence exhibits conserved residues associated with catalytic activity and substrate fixation in other g-type lysozymes. The phylogenetic analysis revealed a high degree of identity of ApGlys with other mollusk g-type lysozymes, which form a restricted and separated clade from the vertebrate lysozymes. ApGlys transcripts were constitutively and highly expressed in the digestive gland, and it was induced in hemocytes and gills of scallops after an immune challenge. Furthermore, the ApGlys protein was located inside hemocytes of immunostimulated scallops, determined by immunofluorescence analysis. Finally, the transcript silencing of ApGlys by RNA interference led to an increase of total culturable bacteria from the scallop hemolymph. Furthermore, we detected a higher diversity of the bacterial community in ApGlys-silenced scallops and an imbalance of certain bacterial groups present in the hemolymph by 16S rDNA deep amplicon sequencing. Overall, our results showed that ApGlys is a new member of scallop lysozymes that is implicated in the immune response and in the microbial homeostasis of A. purpuratus hemolymph.
Article
The activity of enzymes involved in digestion, energy metabolism, oxidative stress regulation, and immune function in the pearl oyster (Pinctada fucata martensii) was determined at 0, 0.5, 1, 2, 5, 10, 15, and 25 d following exposure to HG and NG to characterize the effects of hypoxia on pearl oysters. The protease activity was significantly higher in HG than in NG at 0.5 and 1 d but significantly lower in HG than in NG at 2, 5, 10, 15, and 25 d. The activity of amylase, lipase, and PK was significantly lower in HG than in NG at 0.5, 1, 2, 5, 10, 15, and 25 d. T-AOC and activity of CAT and LDH were significantly higher in HG than in NG at 0.5, 1, 2, and 5 d but significantly lower in HG than in NG at 10, 15, and 25 d. SOD and GPx activity was significantly higher in HG than in NG at 0.5, 1, 2, and 5 d and significantly lower in HG than in NG at 15 and 25 d. LPO content was significantly higher in HG than in NG at 0.5, 1, 2, 5, 10, 15, and 25 d. AKP activity was significantly lower in HG than in NG at 0.5, 1, 10, 15, and 25 d, but no differences in AKP activity were observed between HG and NG at 2 and 5 d. ACP activity was significantly higher in HG than in NG at 0.5 d and significantly lower in HG than in NG at 1, 2, 5, 10, 15, and 25 d. These changes in digestion, energy metabolism, antioxidant capacity, and immune defense promoted adaptation to early hypoxia. Long-term hypoxia decreased the survival rate of pearl oysters by decreasing involved in digestion, energy metabolism, immune responses, and oxidative stress regulation.
Article
Full-text available
A breakdown in host-bacteria relationships has been associated with the progression of a number of marine diseases and subsequent mortality events. For the Pacific oyster, Crassostrea gigas, summer mortality syndrome (SMS) is one of the biggest constraints to the growth of the sector and is set to expand into temperate systems as ocean temperatures rise. Currently, a lack of understanding of natural spatiotemporal dynamics of the host-bacteria relationship limits our ability to develop microbially based monitoring approaches. Here, we characterised the associated bacterial community of C. gigas, at two Irish oyster farms, unaffected by SMS, over the course of a year. We found C. gigas harboured spatiotemporally variable bacterial communities that were distinct from bacterioplankton in surrounding seawater. Whilst the majority of bacteria-oyster associations were transient and highly variable, we observed clear patterns of stability in the form of a small core consisting of six persistent amplicon sequence variants (ASVs). This core made up a disproportionately large contribution to sample abundance (34 ± 0.14%), despite representing only 0.034% of species richness across the study, and has been associated with healthy oysters in other systems. Overall, our study demonstrates the consistent features of oyster bacterial communities across spatial and temporal scales and provides an ecologically meaningful baseline to track environmental change.
Article
Bivalves are an important source of animal protein for human consumption. Multiple lines of evidence have shown that the drivers of climate change have a deleterious impact on bivalve production. Some drivers of climate change, especially global warming and ocean acidification, have previously been comprehensively reviewed for their impact on farmed bivalves. However, the impact of severe winters, a less well-known climate change driver but nonetheless an important factor affecting bivalves, has received far little attention. Therefore, this article reviews the relevant data published on specific research questions to improve the understanding of diverse evidence. In general, the frequency of severe winters is increasing in mid-latitudes, especially in North America, Europe, and Asia. Multiple lines of evidence, ranging from time series field observations to climate change simulation experiments, showed that the increasingly severe winter events led to the mortality of various bivalves. Moreover, severe winters altered the gonadal development pattern, spawning time, and spawning period (species-specific) of bivalves to a certain extent. Interestingly, severe winter promotes the recruitment and lipid nutritional quality of bivalves. To the best of our knowledge, this is the first article to review the impact of severe winters on bivalves. This review is helpful to clarify the current state of research and determine the research direction for the impact of severe winters on bivalves in the future.
Article
The Pacific oyster, Crassostrea gigas is an aquaculture important species and contributed significantly to total seafood production. Unfortunately, the C. gigas aquaculture industry is limited by cold water in high latitudes. On the other hand, C. angulata is well adapted to warm water but its size is much smaller. The present paper describes a comparative study of aquaculture performance of C. gigas, C. angulata and their hybrids in warm water. The growth, survival and lipid nutritional quality of inbred and hybrid oysters were monitored for one year and used as indicators to identify candidates suitable for oyster aquaculture in warm water. The main novelty of this study is the higher growth and survival rates observed in C. angulata relative to C. gigas, and the occurrence of hybrid vigour for growth and survival. Among the oysters, ♀C. angulata x ♂ C. gigas hybrid has achieved the best aquaculture results in the Shantou water on the southern coast of China. The findings of the present study suggest that oyster hybridization can be an effective way to improve the beneficial traits of oyster for aquaculture, including fast growth, high survival rate and well tolerate to warm water temperature at lower latitudes.
Article
Full-text available
Bivalve aquaculture is an important source of affordable animal protein for coastal community. The success and sustainability of this industry is highly influenced by the suitability of the environment in which it is carried out. Present study was carried out to evaluate the feasibility of green mussel (Perna viridis) farming in Marudu Bay. The site suitability for green mussel farming was evaluated based on biophysical parameters and food availability. The in situ environmental parameters, phytoplankton abundance and composition were collected from 10 sampling stations on monthly interval from May 2014 to April 2015. The results showed that the environmental parameters and food availability in most of the sampling stations were suitable for green mussel. However, the presence of phytoplankton taxa (Chaetoceraceae) which are unfavorable by green mussel in most of the stations located at the bay pocket make those areas less recommended for green mussel farming. In contrast, stations located on the mouth of the bay exhibited high site suitability rating points and hence are highly recommended for cultivation of green mussel.
Article
Full-text available
Significance Phytoplankton play essential roles in marine food webs and global biogeochemical cycles, yet the responses of individual species and entire phytoplankton communities to anthropogenic climate change in the coming century remain uncertain. Here we map the biogeographies of commonly observed North Atlantic phytoplankton and compare their historical (1951–2000) and projected future ranges (2051–2100). We find that individual species and entire communities move in space, or shift, and that communities internally reassemble, or shuffle. Over the coming century, most but not all studied species shift northeastward in the basin, moving at a rate faster than previously estimated. These pronounced ecological changes are driven by dynamic changes in ocean circulation and surface conditions, rather than just warming temperatures alone.
Article
Full-text available
Sandy beaches are being threatened by a changing climate. However, the effects of this changing environment, including warming, on these ecosystems, have hitherto been tentative and qualitative. Using concurrent long-term (1984?2007) observations on abundance and individual size, together with laboratory examinations of body abnormalities (morphological anomalies and epibionts), we provide evidence that the sandy beach yellow clam Mesodesma mactroides of the Uruguayan coast has responded to climate change. Regional sea surface temperature anomalies (SSTA) showed an increasing trend through time, with positive values after 1997. The position of the warm water front (20C isotherm), a proxy of tropical waters, showed a long-term poleward shift rate of ca. 9 kmyr?1.Clam abundance (total and discriminated by population component) decreased through time and was inversely related to variations in SSTA, with higher abundance during cold periods. Length frequency distributions (LFDs) showed polymodal size structures with fully represented clam population components in cool years. By contrast, LFDs showed fewer size classes and larger clams were virtually absent during warm years. Prevalence of body abnormalities in M. mactroides increased through time and was positively correlated with increasing SSTA, suggesting a link with climate stress. The population dynamics of M. mactroides seems to be driven by climatic forcing, mostly related with warming. Our results demonstrate the implications of climate change in the structure of sandy beach fauna, which could be particularly relevant in ectotherms with cold water affinities. Thus, climate change should be given a high priority in sandy beach conservation planning and management.
Article
Full-text available
To date, the effects of ocean acidification on toxic metals accumulation and the underlying molecular mechanism remains unknown in marine bivalve species. In the present study, the effects of the realistic future ocean pCO2 levels on the cadmium (Cd) accumulation in the gills, mantle and adductor muscles of three bivalve species, Mytilus edulis, Tegillarca granosa, and Meretrix meretrix, were investigated. The results obtained suggested that all species tested accumulated significantly higher Cd (p < 0.05) in the CO2 acidified seawater during the 30 days experiment and the health risk of Cd (based on the estimated target hazard quotients, THQ) via consumption of M. meretrix at pH 7.8 and 7.4 significantly increased 1.21 and 1.32 times respectively, suggesting a potential threat to seafood safety. The ocean acidification-induced increase in Cd accumulation may have occurred due to (i) the ocean acidification increased the concentration of Cd and the Cd2+/Ca2+ in the seawater, which in turn increased the Cd influx through Ca channel; (ii) the acidified seawater may have brought about epithelia damage, resulting in easier Cd penetration; and (iii) ocean acidification hampered Cd exclusion.
Article
Full-text available
Red tide blooms formed by Karenia brevis are frequent along the Gulf coast of Florida and it is unclear what tolerance the green mussel Perna viridis, a recently introduced species to coastal waters, has toward these events. Established populations of P. viridis were monitored along the coastal waters of Estero Bay, Florida before, during and following two consecutive red tide blooms to assess the potential effects on growth, survival and juvenile recruitment. Upon onset of the bloom, growth rates fell from 6 – 10 mm month-1 (March 2011 – November 2011) to less than 3 mm month-1. In the succeeding years, K. brevis blooms were present, and average growth of individually tagged mussels remained below 3 mm month-1. During growth monitoring the use of calcein as an internal marker was tested with positive staining results and no observed effect on growth or survival. In March 2012, following the first red tide bloom, a population-wide mortality event was observed. Following this event, increased mortality rates were observed with peaks during onset of the bloom in the fall of 2012 and 2013. Juvenile recruitment was also limited during years in which blooms persisted into the spring spawning period suggesting gamete and / or larval sensitivity to K. brevis. Although it cannot be conclusively determined that the cause of reduced growth and survival is due to red tide events, the parallels observed suggest that K. brevis is a factor in the observed changes in population structure.
Article
Full-text available
Seawater acidification and warming resulting from anthropogenic production of carbon dioxide are increasing threats to marine ecosystems. Previous studies have documented the effects of either seawater acidification or warming on marine calcifiers; however, the combined effects of these stressors are poorly understood. In our study, we examined the interactive effects of elevated carbon dioxide partial pressure (pCO2) and temperature on biomineralization and amino acid contents in an ecologically and economically important mussel, Mytilus edulis. The adult M. edulis were reared at different combinations of pCO2 (pH 8.1 and pH 7.8) and temperature (19°C, 22°C, and 25°C) for 2 months. The results indicated that elevated pCO2 significantly decreased the net calcification rate, the calcium content and the Ca/Mg ratio of the shells, induced the differential expression of biomineralization-related genes, modified shell ultrastructure and altered amino acid contents, implying significant effects of seawater acidification on biomineralization and amino acid metabolism. Notably, elevated temperature enhanced the effects of seawater acidification on these parameters. The shell breaking force significantly decreased under elevated pCO2, but the effect was not exacerbated by elevated temperature. The results suggest that the interactive effects of seawater acidification and elevated temperature on mussels are likely to have ecological and functional implications. This study is therefore helpful to better understand the underlying effects of changing marine environments on mussels and other marine calcifiers.
Article
Full-text available
During the summer of 2013, 70 people received Diarrhetic Shellfish Poisoning following consumption of mussels harvested in the Shetland Islands, Scotland. At this time, large numbers of the biotoxin-producing phytoplankton genus Dinophysis was observed around the Shetland Islands. Analysis indicated this increase was not due to in situ growth but coincided with a change in the prevalent wind direction. A previous large bloom of Dinophysis during 2006 also coincided with a similar change in the prevalent wind patterns. Wind direction and speed in the North East Atlantic and the North Sea is strongly influenced by the North Atlantic oscillation (NAO) with a positive relationship between it and wind direction. It has been noted that a positive trend in the NAO is linked to climate change and predictions suggest there will be an increasingly westward component to prevalent wind directions in the North Sea which could lead to an increase in the occurrence of these harmful algal blooms. Analysis of wind patterns therefore offers a potential method of early warning of future bio-toxicity events.
Article
Full-text available
Changes in the physical environment of aquatic systems consistent with climate change have been reported across Australia, with impacts on many marine and freshwater species. The future state of aquatic environments can be estimated by extrapolation of historical trends. However, because the climate is a complex non-linear system, a more process-based approach is probably required, in particular the use of dynamical projections using climate models. Because global climate models operate on spatial scales that typically are too coarse for aquatic biologists, statistical or dynamical downscaling of model output is proposed. Challenges in using climate projections exist; however, projections for some marine and freshwater systems are possible. Higher oceanic temperatures are projected around Australia, particularly for south-eastern Australia. The East Australia Current is projected to transport greater volumes of water southward, whereas the Leeuwin Current on the western coast may weaken. On land, projections suggest that air temperatures will rise and rainfall will decline across much of Australia in coming decades. Together, these changes will result in reduced runoff and hence reduced stream flow and lake storage. Present climate models are particularly limited with regard to coastal and freshwater systems, making the models challenging to use for biological-impact and adaptation studies.
Article
Full-text available
SUMMARY The oyster Crassostrea gasar is a species widely used as food and a source of income for the local population of the estuaries of Northeast Brazil. Perkinsus marinus and Perkinsus olseni are deleterious parasites for oyster farming and were recently detected in Brazil. In this study, a histopathologic survey of the oyster C. gasar cultured in the estuary of the River Mamanguape (Paraíba State) was performed. Adult oysters were collected in December 2011 and March, May, August and October 2012 and processed for histology and Perkinsus sp. identification by molecular analyses. Histopathological analysis revealed the presence of parasitic organisms including viral gametocytic hypertrophy, prokaryote-like colonies, protozoans (Perkinsus sp. and Nematopsis sp.) and metazoans (Tylocephalum sp. and cestodes). Other commensal organisms were also detected (the protozoan Ancistrocoma sp. and the turbellarian Urastoma sp.). The protozoan parasite Perkinsus sp. had the highest overall prevalence among the symbiotic organisms studied (48·9%), followed by Nematopsis sp. (36·3%). The other organisms were only sporadically observed. Only the protozoan Perkinsus sp. caused alterations in the oysters' infected organs. Molecular analyses confirmed the presence of P. marinus, P. olseni and Perkinsus beihaiensis infecting the oyster C. gasar. This is the first report of P. beihaiensis in this oyster species.
Article
Full-text available
In order to assess the effects of ocean acidification and warming on the Mediterranean mussel (Mytilus galloprovincialis), specimens were reared in aquarium tanks and exposed to elevated conditions of temperature (+3°C) and acidity (−0.3 pH units) for a period of 10 months. The whole system comprised a factorial experimental design with 4 treatments (3 aquaria per treatment): control, lowered pH, elevated temperature, and lowered pH/elevated temperature. Mortality was estimated on a weekly basis and every 2 months, various biometrical parameters and physiological processes were measured: somatic and shell growth, metabolic rates and body fluid acid-base parameters. Mussels were highly sensitive to warming, with 100% mortality observed under elevated temperature at the end of our experiment in October. Mortality rates increased drastically in summer, when water temperature exceeded 25°C. In contrast, our results suggest that survival of this species will not be affected by a pH decrease of ~0.3 in the Mediterranean Sea. Somatic and shell growth did not appear very sensitive to ocean acidification and warming during most of the experiment, but were reduced, after summer, in the lowered pH treatment. This was consistent with measured shell net dissolution and observed loss of periostracum, as well as uncompensated extracellular acidosis in the lowered pH treatment indicating a progressive insufficiency in acid-base regulation capacity. However, based on the present dataset, we cannot elucidate if these decreases in growth and regulation capacities after summer are a consequence of lower pH levels during that period or a consequence of a combined effect of acidification and warming. To summarize, while ocean acidification will potentially contribute to lower growth rates, especially in summer when mussels are exposed to sub-optimal conditions, ocean warming will likely pose more serious threats to Mediterranean mussels in this region in the coming decades.
Article
Full-text available
A mass mortality event of blood cockles, Anadara granosa, occurred in aquaculture ground in Selangor in mid-February 2012. To identify factors contributing to this event, we estimated the changes in survival rate and population density of the blood cockles using data from field surveys carried out in late-January and mid-March, 2012. In addition, blood cockle samples were used for histological observation of various tissues with a light microscope. Furthermore, we examined the environmental factors that seemed to be involved in this mass mortality event using environmental data obtained in two surveys and weather data for the Selangor region from late-January to mid-March 2012. As a result of the field surveys and the histological observation, the mortality was estimated to be 30 % over, and the blood cockles were shown to be in the spawning season at this time of year. In addition, numerous individuals collected in mid-March had no food in the digestive duct, which suggested low food availability. Precipitation data for the Selangor region showed rainfall of 30 mm/day over four days in mid-February, which suggested an impact of freshwater flooding from rivers on the aquaculture ground. Normally, the blood cockles are tolerant to low-salinity environments. However, the fact that the flooding and associated environmental changes occurred, when the population was debilitated by reproductive activity, may have led to the mass mortality event in association with low food availability.
Article
Full-text available
Parasitic, disease-causing pathogens can exert strong control over marine populations yet few long-term studies exist that describe these relationships. Understanding the connections to long-term large-scale processes relative to local short-term processes should facilitate better planning for disease impacts in the management of marine resources. We describe a 21-yr dataset of dermo disease (Perkinsus marinus) in eastern oysters (Crassostrea virginica) in Delaware Bay, USA. Analyses indicated (1) a strong positive association between disease and mortality that was non-linear and defined by thresholds, (2) a clear spatial gradient of increasing disease and mortality with increasing salinity, (3) an apparent 7-year cycle in which peaks were associated with strong positive anomalies of the North Atlantic Oscillation (NAO), (4) an inverse relationship with freshwater inflow, and (5) no obvious response to natural selection from persistent disease pressure. These data quantify the impact of environmental variables on the disease in a wild population and provide new insight into how disease interacts with host populations by linking disease patterns with larger climate controlling processes. Understanding these connections will facilitate prediction of and response to disease outbreaks.
Article
Full-text available
Small-scale fisheries (SSFs) are social-ecological systems that play a critical role in terms of food security and poverty alleviation in Latin America. These fisheries are increasingly threatened by anthropogenic and climatic drivers acting at multiple scales. We review the effects of climate variability on Latin American SSFs, and discuss the combined effects of two additional human drivers: globalization of markets and governance. We show drastic long-term and large-scale effects of climate variability, e.g., sea surface temperature anomalies, wind intensity, sea level, and climatic indices, on SSFs. These variables, acting in concert with economic drivers, have exacerbated stock depletion rates in Latin American SSFs. The impact of these drivers varied according to the life cycle and latitudinal distribution of the target species, the characteristics of the oceanographic systems, and the inherent features of the social systems. Our review highlights the urgent need to improve management and governance systems to promote resilience as a way to cope with the increasing uncertainty about the impacts of climate and globalization of markets on Latin American SSFs.
Article
It has been suggested that climate change may promote the outbreaks of diseases in the sea through altering the host susceptibility, the pathogen virulence, and the host-pathogen interaction. However, the impacts of ocean acidification (OA) on the pathogen components of bacterial community and the host-pathogen interaction of marine bivalves are still poorly understood. Therefore, 16S rRNA high-throughput sequencing and host-pathogen interaction analysis between blood clam (Tegillarca granosa) and Vibrio harveyi were conducted in the present study to gain a better understanding of the ecological impacts of ocean acidification. The results obtained revealed a significant impact of ocean acidification on the composition of microbial community at laboratory scale. Notably, the abundance of Vibrio, a major group of pathogens to many marine organisms, was significantly increased under ocean acidification condition. In addition, the survival rate and haemolytic activity of V. harveyi were significantly higher in the presence of haemolymph of OA treated T. granosa, indicating a compromised immunity of the clam and enhanced virulence of V. harveyi under future ocean acidification scenarios. Conclusively, the results obtained in this study suggest that future ocean acidification may increase the risk of Vibrio pathogen infection for marine bivalve species, such as blood clams.
Article
Current study was carried out to provide a better understanding on spatial and temporal variations in the phytoplankton community structure in Marudu Bay, an important nursery ground for fishery resources within the Tun Mustapha Marine Park and Coral Triangle Initiative, and their relationship with environmental variables. Samplings were conducted monthly from April 2014 to April 2015 in Marudu Bay, Malaysia. Water samples were collected for nutrients analysis, zooplankton and phytoplankton counting. Moreover, the in situ environmental parameters were also examined. The field study showed a total of forty seven phytoplankton genera, representative of 33 families were identified. The nutrient concentrations in Marudu Bay was low (mesotrophic) throughout the year, where the phytoplankton community was often dominated by Chaetoceros spp. and Bacteriastrum spp. In general, increase in nitrate concentration triggered the bloom of centric diatom, Chaetoceros spp. and Bacteriastrum spp. in Marudu Bay. However, the bloom of these phytoplankton taxa did not occur in the presence of high ammonia concentration. In addition, high abundance of zooplankton also a limiting factor of the phytoplankton blooms particularly at end of southwest monsoon. High silica concentration promoted the growth of pennate diatoms, Proboscia spp. and Thallassionema spp., but the depletion of silica quickly terminated the bloom. Interestingly, our study showed that Chaetoceros spp., tolerated silica depletion condition, but the average cell size of this taxon reduced significantly. In summary, the phytoplankton community structure in mesotrophic environment is more sensitive to the changes in zooplankton abundance, nutrient concentration and its ratio than that in nutrient rich environments. This study also recommends that bivalve farming at industrial scale is not recommended in Marudu Bay because it potentially depletes the primary productivity hence jeopardizing the availability of live food for larvae of many natural fishery resources in the bay.
Article
Significance This study used high-resolution (daily, quarter-degree resolution) sea-surface temperature records to model trends in growth rates and bloom-season duration for two of the most toxic and widespread harmful algal bloom species indigenous to the North Atlantic and North Pacific oceans. Alexandrium fundyense synthesizes saxitoxin and Dinophysis acuminata synthesizes okadaic acid, which cause the human health syndromes paralytic and diarrhetic shellfish poisoning, respectively. The model provided hindcasts of harmful algal bloom (HAB) events that were consistent with in situ observations from long-term monitoring programs during the same time period. This study provides evidence that increasing ocean temperatures have already facilitated the intensification of these, and likely other, HABs and thus contribute to an expanding human health threat.
Article
The response of microbial assemblages to instantaneous temperature change was measured in a seasonal study of the coastal waters of the western English Channel. On 18 occasions between November 1999 and December 2000, bacterial abundance was assessed and temperature responses determined from the incorporation of (3)H leucine, measured in a temperature gradient from 5-38°C. Q10 values varied, being close to 2 in spring and summer but were >3 in autumn. There was a seasonal pattern in the assemblage optimum temperature (Topt), which was out of phase with sea surface temperature. In July, highest (3)H-leucine incorporation rates were measured at temperatures that were only 2.8°C greater than ambient sea surface temperature but in winter, Topt was ∼20°C higher than the ambient sea surface temperature. Sea surface temperatures for the adjacent English Channel and Celtic Sea for 1982-2014 have periodically been >3°C higher than climatological mean temperatures. This suggests that discrete periods of anomalously high temperatures might be close to, or exceed, temperatures at which maximum microbial assemblage activity occurs. The frequency and magnitude of marine heatwaves are likely to increase as a consequence of anthropogenic climate change and extreme temperatures may influence the role of bacterial assemblages in biogeochemical processes.
Article
Marudu Bay, north coast of Sabah is characterized with mesotrophic water body and typical environmental parameters throughout the year. The current study was undertaken to evaluate the effect of environmental parameters and nutrients in mesotrophic water on the occurrence and distribution of potentially harmful phytoplankton species. The samplings were conducted over a period of thirteen months, covering southwest monsoon (SWM), inter-monsoon (IM), and northeast monsoon (NEM), at ten stations throughout the bay. Physical parameters (temperature, salinity, pH, dissolved oxygen, current speed and secchi depth), biological parameters (cell densities of phytoplankton) and chemical parameters (phosphate, nitrate, silicate and ammonia) were examined. The results indicated at least eight potentially harmful phytoplankton species (Dinophysis caudata, D. miles, Ceratium furca, C. fursus, Prorocentrum micans, P. sigmoides, P. triestinum and Pseudo-nitzschia sp.) were detected in north coast of Sabah. However, the potentially harmful phytoplankton species contributed only about 1.3% of the total phytoplankton community. Under nutrient deprivation conditions, the potentially harmful phytoplankton species distribution was mainly influenced by the ability to utilize other nitrogen sources, cell mobility and toleration to low nutrients environments.
Article
The protozoan parasite Perkinsus marinus is the etiological agent of "dermo disease". This pathogen is considered by the World Organization for Animal Health (OIE) as reportable due to the high mortalities that it produces in the eastern oyster Crassostrea virginica in the US. In 2006, this parasite was detected in the pleasure oyster Crassostrea corteziensis in Nayarit on the Pacific coast of Mexico, indicating a new host and an extension of its known distribution. Epizootiological data of P. marinus in the pleasure oyster are unknown. With the objective of determining the prevalence and intensity in relation with temperature and salinity throughout time, as well as for studying interactions of host size and sex with the parasite, a monthly sampling was carried out in two aquaculture sites of Nayarit from 2007 to 2014. A total of 7,700 oysters were analyzed. In both localities, prevalence was low in winter (< 6%) when temperature and salinity fluctuated around 24°C and 33, respectively; and the highest prevalence values occurred during summer (37%) when temperature and salinity were around 30°C and 20, respectively. Infection intensity increased in summer, but severe cases remained on average < 10%. Larger oysters showed the highest prevalence and intensity, and higher prevalence were generally observed in females. No unusual mortalities directly related with P. marinus were observed.
Article
Coastal embayments are at risk of impacts by climate change drivers such as ocean warming, sea level rise and alteration in precipitation regimes. The response of the ecosystem to these drivers is highly dependent on their magnitude of change, but also on physical characteristics such as bay morphology and river discharge, which play key roles in water residence time and hence estuarine functioning. These considerations are especially relevant for bivalve aquaculture sites, where the cultured biomass can alter ecosystem dynamics. The combination of climate change, physical and aquaculture drivers can result in synergistic/antagonistic and nonlinear processes. A spatially explicit model was constructed to explore effects of the physical environment (bay geomorphic type, freshwater inputs), climate change drivers (sea level, temperature, precipitation) and aquaculture (bivalve species, stock) on ecosystem functioning. A factorial design led to 336 scenarios (48 hydrodynamic × 7 management). Model outcomes suggest that the physical environment controls estuarine functioning given its influence on primary productivity (bottom-up control dominated by riverine nutrients) and horizontal advection with the open ocean (dominated by bay geomorphic type). The intensity of bivalve aquaculture ultimately determines the bivalve-phytoplankton trophic interaction, which can range from a bottom-up control triggered by ammonia excretion to a top-down control via feeding. Results also suggest that temperature is the strongest climate change driver due to its influence on the metabolism of poikilothermic organisms (e.g. zooplankton and bivalves), which ultimately causes a concomitant increase of top-down pressure on phytoplankton. Given the different thermal tolerance of cultured species, temperature is also critical to sort winners from losers, benefiting Crassostrea virginica over Mytilus edulis under the specific conditions tested in this numerical exercise. In general, it is predicted that bays with large rivers and high exchange with the open ocean will be more resilient under climate change when bivalve aquaculture is present.
Article
The current study was carried out from May 2014 to April 2015 to estimate the stock status of P. viridis in Marudu Bay. The gonad development was monitored by histological examination, while the population parameters including asymptotic length (L ∞), growth coefficient (K), mortality rate (Z, F and M), exploitation level (E) and recruitment of P. viridis were estimated using the lengthfrequency data. Results of the current study demonstrated that P. viridis in Marudu Bay spawned throughout the year with two major peaks, one in April to May and another one in October to December. The recruitment pattern was continuous with the peak in May to June 2014, which corresponded to the first spawning peak in April. However, no significant recruitment was observed from the second spawning peak due to the difference in spawning timing between male and female populations. The estimated asymptotic length (L ∞), growth coefficient (K), total mortality (Z), natural mortality (M), fishing mortality (F) and growth performance (ф) of P. viridis in Marudu Bay were estimate to be 117 mm, 0.97 yr-1, 4.39 yr-1, 1.23 yr-1, 3.16 yr-1 and 4.123, respectively. The exponent b of the lengthweight relationship was 2.4 and exploitation level (E) was 0.72. The high mortality, low condition indices and negative allometric of P. viridis in Marudu Bay is caused by a lack of suitable food in the surrounding water.
Article
The green mussel, Perna viridis is known to have the ability to selectively ingest certain suspended particles from water. However, the preferential ingestion of specific phytoplankton taxa by P. viridis under different environmental conditions is not well understood. A study was undertaken to identify the phytoplankton taxa that are preferentially ingested and rejected by P. viridis in different environmental conditions at Marudu Bay, Malaysia. Phytoplankton abundance and composition in stomach and surrounding waters were determined microscopically. The gonad development stages of P. viridis and various environmental parameters of the bay including temperature, salinity, dissolved oxygen, current speed, pH, visibility, chlorophyll a, nutrients concentration and suspended particles were also determined. Results of current study demonstrated that selective ingestion in P. viridis was mainly influenced by seston concentration, phytoplankton abundance and composition. At high seston concentration with low phytoplankton abundance, P. viridis selectively ingested Coscinodiscus spp. In contrast, P. viridis was found to ingest wider range of phytoplankton at low seston concentration and high phytoplankton abundance. Interestingly, Chaetoceros spp. and Bacteriastrum spp. were selectively rejected by P. viridis in both high and low seston conditions. Nevertheless, no selective ingestion behaviour was evidenced in low seston with low phytoplankton conditions. Besides phytoplankton, zooplankton has also contributed significantly in the diet of P. viridis, where high numbers of copepod and bivalve larvae were found in the stomach. The findings of current study can be useful in determining potential farming sites for green mussel in future.
Article
Present study was intended to compare the acute static renewal toxicity tests on marine snail, Cerithidae cingulata and bivalve, Modiolus philippinarum that were performed with Cu, Cd, Pb, Zn and Hg. The 96 h LC 50 values for C.cingulata were 0.521, 9.193, 15.507, 8.990 and 0.053 mg.l-1 and the 96 h LC 50 values for M.philippinarum were 0.023, 0.221, 2.876, 2.337 and 0.007 mg.l -1 in respective metals. This study indicated that mercury was highly toxic to both C.cingulata and M.philippinarum. While lead was resistant metal to both marine molluscs tested. Order of increasing toxicity of metals to C.cingulata was Hg > Cu > Zn> Cd > Pd and to M.philippinarum was Hg > Cu > Cd > Zn > Pb. Safe level concentrations for all 5 metals were also calculated. The LC 50 values of the present study may be useful in deriving marine water quality standards in the coastal waters of Gulf of Mannar.
Article
A study was begun in late 1997 in Puget Sound, Washington, and Tornalas Bay, California, to characterize more precisely the summer mortality of the Pacific oyster (Crassostrea gigas) in a variety of culture conditions and locations and to describe definitively the relationship of summer mortality to infectious diseases. Water quality and seasonal factors also were identified. A field component investigated the oysters' thermal stress response and assessed induced thermal tolerance as a means to reduce mortalities. In addition, management practices for commercial cultivation were evaluated as measures to reduce the frequency and extent of oyster losses. Our evaluation of the 1998 data from the summer mortality project supports earlier reports on the rate and timing of mortality events. There were differences in the mortality rates among the varieties of oysters tested, with triploid oysters having consistently higher mortality rates than diploid oysters planted in comparable plots. Trends in mortalities were toward higher rates at or immediately after neap tides when dissolved oxygen was lowest and during periods of elevated air and water temperatures. Relative densities of the phytoplankton Gymnodinium splendens, Ceratium spp., and Psuedo-nitzschia spp. were higher during the late summer; Dissolved oxygen concentrations were correspondingly low, and oyster mortalities were high during this same period. It is likely that Pacific oysters at the study sites experienced varying degrees of chronic stress attributable to multiple environmental factors. Evaluations of effects of those stressors and development of oyster health management strategies are continuing.
Article
Suspension feeding bivalves, which rely primarily on phytoplankton as their food source, experienced the most dramatic and immediate impact during massive blooms of the newly described chrysophycean Aureococcus anophagefferens (Sieburth et al., 1988). Tracey (1988) reported reproductive failure and mortalities ranging from 30 to 100% of natural and transplanted mussels, Mytilus edulis, in Narragansett Bay, R.I. during the 1985 “brown tide” event. In New York State, the bay scallop fishery was virtually eliminated by two successive “brown tide” episodes occurring during the summers of 1985 and 1986. Bay scallops, Argopecten irradians, are particularly vulnerable to recruitment failure because few individuals survive to spawn more than once during their short (< 2.5 year) lifespan. Peak concentrations of Aureococcus anophagefferens (109 cells 1−1) coincided with the scallops’ spawning season in eastern Long Island waters (June–July), thus leading to recruitment failure and starvation of the post-spawning parental stock (Bricelj et al., 1987b). Although survivors of the 1985 bloom could potentially have contributed to spawning in 1986, occurrence of the bloom on two consecutive years prevented the establishment of new recruits.
Article
From its discovery in 1949 until 1990, the oyster parasite Perkinsus marinus, cause of Dermo disease in the eastern oyster Crassostrea virginica, was found primarily from Chesapeake Bay south along the Atlantic Coast of the United States and into the Gulf of Mexico. In 1990 and 1991, the parasite suddenly appeared in locations from Delaware Bay, NJ, to Cape Cod, MA, a range extending more than 500 km north of Chesapeake Bay. An earlier incursion of the parasite into Delaware Bay in the 1950s, associated with importation of large numbers of infected oysters from Chesapeake Bay, did not cause detectable mortalities or result in the establishment of a significant parasite population. The parasite was no longer detected after imports of infected oysters ceased. In contrast, the epizootic that began in Delaware Bay in 1990 resulted in high disease prevalence and intensity, and caused heavy mortalities, but was not linked to similar imports. Several hypotheses for the sudden appearance of the parasite in the northeastern United States are considered: 1) the parasite was transmitted via infected oysters introduced from enzootic southern areas into northern waters; 2) a change in the genetic structure of either host or parasite increased the parasite's ability to invade and proliferate in the northeast; 3) the environment in the northeastern United States became more favorable for parasite activity; or 4) some combination of these three. The simplest explanation consistent with available data is that the pathogen was repeatedly introduced, by many means over many years, into various northeast locations where it remained undetected and was stimulated to proliferate into an epizootic by a recent extreme warming trend. Above average winter, rather than summer, temperatures were associated with the 1990s epizootic. Also, cold winters, not cool summers, were correlated with the disappearance of P. marinus from Delaware Bay in the 1950s. Stopping or materially slowing the epizootic will probably require a series of consecutive cold (i.e., average or below average temperatures) winters and cool springs that will delay and restrict the proliferation of parasites during the following summer. Eliminating the parasite from its new range may be difficult even with cooler temperatures, however, as the development of low temperature-adapted parasites could occur now that large populations are established in a region where selection pressure exists for this trait.
Article
Perkinsus marinus (Mackin, Owen and Collier) is a major cause of mortality of eastern oysters, Crassostrea virginica (Gmelin), along the Gulf of Mexico. The parasite is discontinuously distributed in estuaries from Tabasco, Mexico, to the Everglades of Florida. Its distribution is essentially coincident with its oyster host, although oysters survive well at salinities slightly lower than those tolerated by the parasite. Besides a low-salinity refuge, Gulf oysters apparently adapt to parasitic challenge with high recruitment and fast growth, which allows them to respond to natural estuarine variability more quickly than the parasite can. Temperature and salinity, but particularly their interaction, are important environmental influences on levels of Perkinsus in oysters. Most of the variation in levels of infection, however, are not explained by these factors. Other environmental and biological factors must affect the levels of parasitism observed in the field. These likely include, but are not limited to, pollution and other human influences, host nutrition and growth, spawning and reproduction, age and resistance, oyster density and distribution, and disease vectors.
Article
Large-scale red tides of Heterocapsa sp. (Dinophyceae) occurred in Ago Bay during the summer and autumn of 1992. The seawater was discolored to yellow brown, and the maximum cell density was 87, 420 cells/ml. The summer red tide occurred from mid to late August, and the autumn red tide from late October to late November. Water temperatures and the salinities were 23.8 to 26.9 °C and 33.2 to 33.4 during the summer red tide, and 16.9 to 22.2 °C and 30.5 to 32.2 during the autumn red tide. Thus, Heterocapsa sp. can form red tides over a wide range of water temperature. The autumn red tide developed slowly as compared to the summer one. This may be due in part to the lower water temperature in autumn. Both red tides were preceded by heavy rainfall and/or vertical mixing of the seawater associated with a typhoon. It is suggested that these physical events promoted and supported the growth of this species. The red tides caused mass mortality of pearl oysters (Pinctada fucata); however, mortalities of cultured and feral fish were not observed. During the red tides, pearl oysters closed their shells tightly and died despite the high concentration of dissolved oxygen. This is the first report of Heterocapsa sp. red tides causing mass mortaliy of pearl oysters in Japan.
Article
Mass mortalities of Pacific oysters Crassostrea gigas occur regularly when temperatures are high. Elevated temperatures facilitate the proliferation and spread of pathogens and simultaneously impose physiological stress on the host. Additionally, periods of high temperatures coincide with the oyster spawning season. Spawning is energetically costly and can further compromise oyster immunity. Most studies monitoring the underlying factors of oyster summer mortality in the field, point to the involvement of abiotic and biotic factors including low salinities, high temperatures, pollutants, toxic algae blooms, pathogen exposure and physical stress in conjunction with maturation. However, studies addressing more than two factors experimentally are missing thus far. Therefore, we investigated the combination of three main factors including abiotic as well as internal and external biotic stressors by conducting controlled infection experiments on pre-and post-spawning as well as on gravid oysters with opportunistic Vibrio sp. at two different temperatures. Based on mortality rates, infection intensity and cellular immune parameters, we provide experimental evidence that all three factors (i.e. reproductive investment, elevated temperatures and infection with opportunistic Vibrio sp.) act additively to the phenomenon of oyster summer mortality, leaving post-spawning oyster more susceptible to SMS than pre-spawning and gravid oysters. While previous studies found that post-spawning oysters have a lower thermal tolerance and a reduced ability to withstand pathogen infections, our study now allows to separate the relative contribution of different causative agents to oyster summer mortality and pinpoint to infection with pathogenic Vibrio sp. being of highest importance. In addition we can add a mechanistic understanding for the higher losses after spawning during which the phagocytic ability of hemocytes was strongly impeded resulting in insufficient clearance of pathogens.
Article
1. Twelve strains of bacteria were isolated from a moribund Venus mercenaria larva in a laboratory culture. These, ten other clones, and mixed bacteria from sea water were assayed by adding broth culture yielding 106-107 cells/ml. to beaker cultures of healthy clam larvae. Only the mixed bacterial culture from the moribund larva and two of the 12 strains isolated from it caused extensive mortality. One of the virulent clones (6-) is a species of Vibrio,the other (13-1) is a Pseudomonas species.2. Larvae exposed to virulent bacteria and simultaneously treated with antibiotics were as healthy as controls, showing that active bacteria were necessary to destroy larvae and that metabolites in the bacterial inoculum were not harmful to larvae.3. Larvae were grown free of contaminating micro-organisms by allowing washed eggs to develop in antibiotic solutions and then isolating straight-hinge larvae by pipette. Either virulent clone (106-107/ml.) destroyed 10-100% of such larvae. However, exposing the animals to...
Article
The marine dinoflagellate Heterocapsa circularisquama Horiguchi is the causal agent of red tide on the Japanese coast. In the last decade, H. circularisquama red tides have destroyed the shellfish aquaculture industries around the western part of Japan because this dinoflagel-late shows a detrimental effect on shellfishes particularly on bivalve molluscs. The current proliferation of H. circularisquama throughout western Japan is a cause for concern due to economic loss. The outbreaks of H. circularisquama are closely related to the environmental conditions: water exchange rate, water temperature, local and global climate changes. Administrative measures such as algal monitoring systems can be successfully utilized for the distribution and short-term prediction of red tide due to H. circularisquama in several locations. However, secondary damage, i.e. decline of demand due to misinformation and cost of measures to prevent the damage, adversely affects the development of shellfish aquaculture even if direct killing of the products can be avoided.
Article
The incidence of red tide events globally has escalated in marine coastal environments over the last several decades (Cordier et al. 2000). The term red tide is used to describe a phenomenon in which a water body exhibits red coloration from the presence of high algal cell density. Red tide events are often harmful to both human and aquatic organisms. However, the term may be confusing, because red tide refers not only to the high density of microscopic algal cells that colorize water, but also includes blooms of highly toxic cells that can cause problems even at low cell densities, i.e., a few hundred cells L−1. Therefore, the term Harmful Algal Blooms (HABs) has been introduced to describe blooms of both toxic and non-toxic algae that potentially have negative effects on humans and the environment (Anderson 2009). The reported global incidence of paralytic shellfish poisoning (PSP) that has been associated with HABs has been increasing annually (Anderson 1989). However, it is still unclear whether the increase results from elevated public awareness and reporting of HABs, or from an increase in anthropogenic factors, like increasing marine pollution incidents.
Article
The dinoflagellate, Heterocapsa circularisquama Horiguchi is known to cause massive marine shellfish deaths in coastal waters of Japan. During the last two decades, proliferation of H. circularisquama across western portions of Japan hampered the production of shellfish cultivation, resulting in economic consequences. In this chapter, the ecophysiology and toxicology of H. circularisquama and subsequent damage to aquaculture are discussed, with special emphasis on the effects of H. circularisquama on the physiology of shellfish.
Article
There has been no consensus on whether Prorocentrum minimum is “toxic,” despite sporadic reports suggesting possible shellfish toxicity and laboratory studies showing harmful effects of this dinoflagellate on molluscan shellfish. Shellfish toxicity outbreaks associated with natural blooms of P. minimum have been confounded by co-occurrence of other toxic phytoplankton. Laboratory studies have demonstrated unequivocally that some P. minimum isolates can produce toxins that kill mice on injection, but the bioactive compound or compounds remain unidentified, and accumulation of toxin in grazing mollusks has not been demonstrated. Laboratory experiments testing the responses of grazing mollusks to P. minimum cultures have yielded variable results, ranging from mortality in scallops and oysters to normal growth of oysters. Effects observed in the laboratory include rejection as pseudofeces by clams, poor larval development in oysters, tissue pathologies (sometimes transient) in oysters and scallops, and systemic immune responses in oysters and scallops. Several recent studies have provided evidence that variation in toxicity of P. minimum is dependent on environmental conditions and their effects on the physiology of this dinoflagellate. Accordingly, seemingly conflicting observations from field and laboratory studies may be explained by transient toxin expression in P. minimum.
Article
From its initial discovery in the Gulf of Mexico in the late 1940s until 1990,Perkinsus marinus, the parasite responsible for Dermo disease in the eastern oyster,Crassostrea virginica, was rarely found north of Chesapeake Bay. In 1990–92, an apparent range extension of the parasite led to epizootic outbreaks of the disease over a 500 km range north of Chesapeake Bay. One of the hypotheses for the range extension argues that small, undetected numbers of parasites were already present in northern oysters as the result of repeated historical introductions, and that a sharp warming trend in 1990–92 stimulated the disease outbreak. This argument was based on trends in air temperature. The present study examined this hypothesis by analysing water temperatures, rather than air temperatures, for five stations located in areas affected by the recent epizootics. At all five stations, there was a strong increasing trend in winter sea-surface temperature (SST) between 1986 and 1991. At four of the five stations, there was a smaller increasing trend in winter temperatures after 1960. There were no consistent or obvious trends in summer (August) temperatures. In Delaware Bay, which has a 40 year history of monitoring for oyster diseases, occasional findings ofP. marinusin oysters were correlated with warming episodes that were especially notable in the winter (February) record. Empirical orthogonal function (EOF) analysis showed that winter temperatures varied consistently at the stations examined and were associated with variations inP. marinusprevalence. Associations using EOF analysis with August temperatures were much weaker. The SST record is consistent with the hypothesis that increasing winter water temperatures have been important in the recent outbreak ofP. marinusepizootics in the north-eastern U.S.A.