Pathogenic marine microbes influence the effects of climate change on a commercially important tropical bivalve

Microbiota characterization of the green mussel Perna viridis at the tissue scale and its relationship with the environment

Research on the microbiota associated with marine invertebrates is important for understanding host physiology and the relationship between the host and the environment. In this study, the microbiota of the green mussel Perna viridis was characterized at the tissue scale using 16S rRNA gene high-throughput sequencing and compared with the microbiota of the surrounding environment. Different mussel tissues were sampled, along with two environmental samples (the mussel's attachment substratum and seawater). The results showed that the phyla Proteobacteria, Bacteroidetes, and Spirochaetae were dominant in mussel tissues. The bacterial community composition at the family level varied among the tissues of P. viridis. Although the microbiota of P. viridis clearly differed from that of the surrounding seawater, the composition and diversity of the microbial community of the foot and outer shell surface were similar to those of the substratum, indicating their close relationship with the substratum. KEGG prediction analysis indicated that the bacteria harbored by P. viridis were enriched in the degradation of aromatic compounds, osmoregulation, and carbohydrate oxidation and fermentation, processes that may be important in P. viridis physiology. Our study provides new insights into the tissue-scale characteristics of mussel microbiomes and the intricate connection between mussels and their environment.

Investigation of the highly endangered Pinna nobilis' mass mortalities: Seasonal and temperature patterns of health status, antioxidant and heat stress responses

Recently, P. nobilis populations have suffered a tremendous reduction, with pathogens potentially playing a crucial role. Considering its highly endangered status, mechanisms leading to mass mortalities were examined in one or multiple pathogens infected populations. Thus, seasonal antioxidant enzymatic activities, hsp70 and catalase mRNA levels, were investigated in two different Greek populations, during mass mortality events in summer of 2020. Samples were collected from Fthiotis and Lesvos during February (T^oC 14 ± 1.2 and 15 ± 1 respectively), April (T^oC 18 ± 1.2 and 17 ± 1.3 respectively), and June (T^oC 24.5 ± 1.5 and 21.5 ± 1.5 respectively) 2020. In July of the same year (T^oC 26.5 ± 1.7 in Fthiotis and 24.5 ± 1.7 in Lesvos), no live specimens were found. All biochemical parameters and phylogenetic analysis suggest that pathogen infection increases P. nobilis sensitivity to water temperature, subsequently leading to mass mortality. The latter was obvious in Fthiotis individuals, in which Haplosporidium pinnae was also observed with Mycobacterium spp., compared to Lesvos individuals.

Shellfish-algal systems as important components of fisheries carbon sinks: Their contribution and response to climate change

In the context of global climate change, ocean acidification and warming are becoming increasingly serious. Adding carbon sinks in the ocean is an important part of efforts to mitigate climate change. Many researchers have proposed the concept of a fisheries carbon sink. Shellfish-algal systems are among the most important components of fisheries carbon sinks, but there has been limited research on the impact of climate change on shellfish-algal carbon sequestration systems. This review assesses the impact of global climate change on shellfish-algal carbon sequestration systems and provides a rough estimate of the global shellfish-algal carbon sink capacity. This review evaluates the impact of global climate change on shellfish-algal carbon sequestration systems. We review relevant studies that have examined the effects of climate change on such systems from multiple levels, perspectives, and species. There is an urgent need for more realistic and comprehensive studies given expectations about the future climate. Such studies should provide a better understanding of the mechanisms by which the carbon cycle function of marine biological carbon pumps may be affected in realistic future environmental conditions and the patterns of interaction between climate change and ocean carbon sinks.

Future Climate Change Conditions May Compromise Metabolic Performance in Juveniles of the Mud Crab Scylla serrata

Research characterising the effects of future climate change on the marine environment remains heavily focussed on that of temperate regions and organisms. Furthermore, little is known of these effects on the early life stages of many marine species. Tropical regions are already experiencing an increase in sea surface temperature and decrease in sea surface salinity, conditions favoured by pathogenic bacteria such as Vibrio spp. The early life stages of crabs are known to be particularly vulnerable to both the direct physiological effects of climate change and exposure to harmful microorganisms, yet there are limited data on these effects on juveniles of many tropical crustacean species. This study assessed the metabolic responses of mud crab (Scylla serrata) juveniles to warming and/or freshening in the presence or absence of pathogenic bacteria in southwest India. Juvenile crabs were exposed to either ambient (28 °C/30 PSU) or one of three projected climate change regimes (28 °C/20 PSU (freshening), 32 °C/30 PSU (warming), 32 °C/20 PSU (warming + freshening)) for 10 days, in either the presence or absence of the pathogenic bacteria Vibrio parahaemolyticus. Results show that simulated climate change conditions, especially freshening, caused a significant increase in oxygen consumption rates (MO2), and that these were further increased when juveniles were exposed to V. parahaemolyticus. These results suggest that the effects of future climate change conditions could have significant implications for the conservation of wild stocks and commercial farming of this species in South Asia.

Algicidal Bacteria: A Review of Current Knowledge and Applications to Control Harmful Algal Blooms

Interactions between bacteria and phytoplankton in aqueous ecosystems are both complex and dynamic, with associations that range from mutualism to parasitism. This review focuses on algicidal interactions, in which bacteria are capable of controlling algal growth through physical association or the production of algicidal compounds. While there is some evidence for bacterial control of algal growth in the field, our understanding of these interactions is largely based on laboratory culture experiments. Here, the range of these algicidal interactions is discussed, including specificity of bacterial control, mechanisms for activity, and insights into the chemical and biochemical analysis of these interactions. The development of algicidal bacteria or compounds derived from bacteria for control of harmful algal blooms is reviewed with a focus on environmentally friendly or sustainable methods of application. Potential avenues for future research and further development and application of bacterial algicides for the control of algal blooms are presented.

The current situation and potential effects of climate change on the microbial load of marine bivalves of the Greek coastlines: an integrative review

Global warming affects the aquatic ecosystems, accelerating pathogenic microorganisms' and toxic microalgae's growth and spread in marine habitats, and in bivalve molluscs. New parasite invasions are directly linked to oceanic warming. Consumption of pathogen-infected molluscs impacts human health at different rates, depending, inter alia, on the bacteria taxa. It is therefore necessary to monitor microbiological and chemical contamination of food. Many global cases of poisoning from bivalve consumption can be traced back to Mediterranean regions. This article aims to examine the marine bivalve's infestation rate within the scope of climate change, as well as to evaluate the risk posed by climate change to bivalve welfare and public health. Biological and climatic data literature review was performed from international scientific sources, Greek authorities and State organizations. Focusing on Greek aquaculture and bivalve fisheries, high-risk index pathogenic parasites and microalgae were observed during summer months, particularly in Thermaikos Gulf. Considering the climate models that predict further temperature increases, it seems that marine organisms will be subjected in the long term to higher temperatures. Due to the positive linkage between temperature and microbial load, the marine areas most affected by this phenomenon are characterized as 'high risk' for consumer health.

Impact of heavy precipitation events on pathogen occurrence in estuarine areas of the Puzi River in Taiwan

Pathogen populations in estuarine areas are dynamic, as they are subject to multiple natural and anthropogenic challenges. Heavy rainfall events bring instability to the aquatic environment in estuaries, causing changes in pathogen populations and increased environmental sanitation and public health concerns. In this study, we investigated the effects of heavy precipitation on the occurrence of pathogens in the Puzi River estuary, which is adjacent to the largest inshore oyster farming area in Taiwan. Our results indicated that Vibrio parahaemolyticus and adenovirus were the most frequently detected pathogens in the area. There was a significant difference (Mann-Whitney U test, p < 0.01) in water quality parameters, including total coliform, Escherichia coli, water temperature, turbidity, salinity, and dissolved oxygen, between groups with and without V. parahaemolyticus. In addition, the detection rate was negatively correlated with the average daily rainfall (r2 > 0.8). There was no significant difference between water quality parameters and the presence/absence of adenovirus, but a positive correlation was observed between the average daily rainfall and the detection rate of adenovirus (r2 ≥ 0.75). We conclude that heavy precipitation changes estuarine water quality, causing variations in microbial composition, including pathogens. As extreme weather events become more frequent due to climate change, the potential impacts of severe weather events on estuarine environments require further investigation.

Future foods for risk-resilient diets

Future foods, such as microalgae, mycoprotein and mealworm, have been suggested as nutritious and sustainable dietary options. Here we consider one of the most profound, yet neglected, benefits of future foods farming systems-their potential to provide essential nutrition in the face of systemic disturbances-and discuss major barriers to realizing this prospect.

Shellfish Toxin Uptake and Depuration in Multiple Atlantic Canadian Molluscan Species: Application to Selection of Sentinel Species in Monitoring Programs

Shellfish toxin monitoring programs often use mussels as the sentinel species to represent risk in other bivalve shellfish species. Studies have examined accumulation and depuration rates in various species, but little information is available to compare multiple species from the same harvest area. A 2-year research project was performed to validate the use of mussels as the sentinel species to represent other relevant eastern Canadian shellfish species (clams, scallops, and oysters). Samples were collected simultaneously from Deadmans Harbour, NB, and were tested for paralytic shellfish toxins (PSTs) and amnesic shellfish toxin (AST). Phytoplankton was also monitored at this site. Scallops accumulated PSTs and AST sooner, at higher concentrations, and retained toxins longer than mussels. Data from monitoring program samples in Mahone Bay, NS, are presented as a real-world validation of findings. Simultaneous sampling of mussels and scallops showed significant differences between shellfish toxin results in these species. These data suggest more consideration should be given to situations where multiple species are present, especially scallops.

Influence of climatic factors on the temporal occurrence and distribution of total and pathogenic Vibrio parahaemolyticus in oyster culture environments in Taiwan

This study evaluated the occurrence and distribution of total and pathogenic V. parahaemolyticus in oyster culture environments in Taiwan. V. parahaemolyticus levels in oysters, seawater, and sediment were quantified using the most probable number (MPN) method combined with a qualitative polymerase chain reaction (PCR). Total V. parahaemolyticus was determined based on the presence or absence of tlh gene, whereas pathogenic V. parahaemolyticus was determined based on the detection of tdh and/or trh gene. The results showed that: 1) V. parahaemolyticus was detected in 93% of the collected samples, 2) the mean concentrations of total V. parahaemolyticus in oysters, seawater, and sediment were 4.1 log MPN/g, 2.1 log MPN/mL, and 4.2 log MPN/g, respectively, and 3) variations in the abundance of V. parahaemolyticus was significantly associated with sea surface temperature (SST). Findings in this study could be used to improve the accuracy of the risk assessment model for V. parahaemolyticus in oysters in Taiwan.

Bioremediation with freshwater bivalves: A sustainable approach to reducing the environmental impact of inland trout farms

Integrated multi trophic aquaculture (IMTA) is well developed in seawater, while the only suitable organisms for bioremediation in freshwater are bivalves. The aim of this research has been to investigate a novel system, based on freshwater bivalves integrated with rainbow trout, for the bioremediation of inland aquaculture systems. The Unionid species selected for the experiments was Sinanodonta woodiana. Five mesocosm experiments were conducted to evaluate the efficiency of mussels in filtering the total bacteria and Aeromonas hydrophila, as well as their clearance efficiency on trout farm wastewater. The temperatures, dissolved oxygen, nitrates, and phosphates were monitored and were all within the physiological tolerance range of the species in all the experiments. The feasibility of bioremediation with S. woodiana in trout farming has thus been demonstrated, and among the tested rearing densities (3.75; 7.5; 15; 30 and 60 kg m^-3) that of 7.5 kg m^-3 was found to be optimal. The net reduction of the total bacterial concentration was as much as 72%, while that of A. hydrophila reached a level of 95-98%. No relevant effects of the mussels on particulate suspended material or sedimented material was observed, regardless of the temperature. The efficiency of freshwater bivalves in reducing the bacterial load, in particular toward A. hydrophila, indicates a bioremediation system with the possibility of interesting applications on inland fish farms, and as a biotechnological tool against the diffusion of antibiotic resistance in aquaculture.

Effects of marine harmful algal blooms on bivalve cellular immunity and infectious diseases: A review

Bivalves were long thought to be "symptomless carriers" of marine microalgal toxins to human seafood consumers. In the past three decades, science has come to recognize that harmful algae and their toxins can be harmful to grazers, including bivalves. Indeed, studies have shown conclusively that some microalgal toxins function as active grazing deterrents. When responding to marine Harmful Algal Bloom (HAB) events, bivalves can reject toxic cells to minimize toxin and bioactive extracellular compound (BEC) exposure, or ingest and digest cells, incorporating nutritional components and toxins. Several studies have reported modulation of bivalve hemocyte variables in response to HAB exposure. Hemocytes are specialized cells involved in many functions in bivalves, particularly in immunological defense mechanisms. Hemocytes protect tissues by engulfing or encapsulating living pathogens and repair tissue damage caused by injury, poisoning, and infections through inflammatory processes. The effects of HAB exposure observed on bivalve cellular immune variables have raised the question of possible effects on susceptibility to infectious disease. As science has described a previously unrecognized diversity in microalgal bioactive substances, and also found a growing list of infectious diseases in bivalves, episodic reports of interactions between harmful algae and disease in bivalves have been published. Only recently, studies directed to understand the physiological and metabolic bases of these interactions have been undertaken. This review compiles evidence from studies of harmful algal effects upon bivalve shellfish that establishes a framework for recent efforts to understand how harmful algae can alter infectious disease, and particularly the fundamental role of cellular immunity, in modulating these interactions. Experimental studies reviewed here indicate that HABs can modulate bivalve-pathogen interactions in various ways, either by increasing bivalve susceptibility to disease or conversely by lessening infection proliferation or transmission. Alteration of immune defense and global physiological distress caused by HAB exposure have been the most frequent reasons identified for these effects on disease. Only few studies, however, have addressed these effects so far and a general pattern cannot be established. Other mechanisms are likely involved but are under-studied thus far and will need more attention in the future. In particular, the inhibition of bivalve filtration by HABs and direct interaction between HABs and infectious agents in the seawater likely interfere with pathogen transmission. The study of these interactions in the field and at the population level also are needed to establish the ecological and economical significance of the effects of HABs upon bivalve diseases. A more thorough understanding of these interactions will assist in development of more effective management of bivalve shellfisheries and aquaculture in oceans subjected to increasing HAB and disease pressures.

Toxic Algae Silence Physiological Responses to Multiple Climate Drivers in a Tropical Marine Food Chain

Research on the effects of climate change in the marine environment continues to accelerate, yet we know little about the effects of multiple climate drivers in more complex, ecologically relevant settings - especially in sub-tropical and tropical systems. In marine ecosystems, climate change (warming and freshening from land run-off) will increase water column stratification which is favorable for toxin producing dinoflagellates. This can increase the prevalence of toxic microalgal species, leading to bioaccumulation of toxins by filter feeders, such as bivalves, with resultant negative impacts on physiological performance. In this study we manipulated multiple climate drivers (warming, freshening, and acidification), and the availability of toxic microalgae, to determine their impact on the physiological health, and toxin load of the tropical filter-feeding clam, Meretrix meretrix. Using a structural equation modeling (SEM) approach, we found that exposure to projected marine climates resulted in direct negative effects on metabolic and immunological function and, that these effects were often more pronounced in clams exposed to multiple, rather than single climate drivers. Furthermore, our study showed that these physiological responses were modified by indirect effects mediated through the food chain. Specifically, we found that when bivalves were fed with a toxin-producing dinoflagellate (Alexandrium minutum) the physiological responses, and toxin load changed differently and in a non-predictable way compared to clams exposed to projected marine climates only. Specifically, oxygen consumption data revealed that these clams did not respond physiologically to climate warming or the combined effects of warming, freshening and acidification. Our results highlight the importance of quantifying both direct and, indirect food chain effects of climate drivers on a key tropical food species, and have important implications for shellfish production and food safety in tropical regions.

Microdevice-based solid-phase polymerase chain reaction for rapid detection of pathogenic microorganisms

We demonstrate the integration of DNA amplification and detection functionalities developed on a lab-on-a-chip microdevice utilizing solid-phase polymerase chain reaction (SP-PCR) for point-of-need (PON) DNA analyses. First, the polycarbonate microdevice was fabricated by thermal bonding  to contain microchambers as reservoirs for performing SP-PCR. Next, the microchambers were subsequently modified with polyethyleneimine and glutaraldehyde for immobilizing amine-modified forward primers. During SP-PCR, the immobilized forward primers and freely diffusing fluorescence-labeled reverse primers cooperated to generate target amplicons, which remained covalently attached to the microchambers for the fluorescence detection. The SP-PCR microdevice was used for the direct identifications of two widely detected foodborne pathogens, namely Salmonella spp. and Staphylococcus aureus, and an alga causing harmful algal blooms annually in South Korea, Cochlodinium polykrikoides. The SP-PCR microdevice would be versatilely applied in PON testing as a universal platform for the fast identification of foodborne pathogens and environmentally threatening biogenic targets.