The long-lived deep-sea bivalve Acesta excavata is sensitive to the dual stressors of sediment and warming.

Human influence in the deep-sea is increasing as mining and drilling operations expand, and waters warm because of climate change. Here, we investigate how the long-lived deep-sea bivalve, Acesta excavata responds to sediment pollution and/or acute elevated temperatures. A. excavata were exposed to suspended sediment, acute warming, and a combination of the two treatments for 40 days. We measured O2 consumption, NH4+ release, Total Organic Carbon (TOC), and lysosomal membrane stability (LMS). We found suspended sediment and warming interacted to decrease O:N ratios, while sediment as a single stressor increased the release of TOC and warming increased NH4+ release in A. excavata. Warming also increased levels of LMS. We found A. excavata used protein catabolism to meet elevated energetic demands indicating a low tolerance to stress. A. excavata has limited capacity for physiological responses to the stressors of warming and sediment which may lead to decreased fitness of A. excavata.

Effects of elevated temperature and different crystal structures of TiO2 nanoparticles on the gut microbiota of mussel Mytilus coruscus.

Coastal habitats are exposed to increasing pressure of nanopollutants commonly combined with warming due to the seasonal temperature cycles and global climate change. To investigate the toxicological effects of TiO2 nanoparticles (TiO2 NPs) and elevated temperature on the intestinal health of the mussels (Mytilus coruscus), the mussels were exposed to 0.1 mg/L TiO2 NPs with different crystal structures for 14 days at 20 °C and 28 °C, respectively. Compared to 20 °C, the agglomeration of TiO2 NPs was more serious at 28 °C. Exposure to TiO2 NPs led to elevated mortality of M. coruscus and modified the intestinal microbial community as shown by 16S rRNA sequence analysis. Exposure to TiO2 NPs changed the relative abundance of Bacteroidetes, Proteobacteria and Firmicutes. The relative abundances of putative mutualistic symbionts Tenericutes and Fusobacteria increased in the gut of M. coruscus exposed to anatase, which have contributed to the lower mortality in this group. LEfSe showed the combined stress of warming and TiO2 NPs increased the risk of M. coruscus being infected with potential pathogenic bacteria. This study emphasizes the toxicity differences between crystal structures of TiO2 NPs, and will provides an important reference for analyzing the physiological and ecological effects of nanomaterial pollution on bivalves under the background of global climate change.

Combined effects of microfibers and polychlorinated biphenyls on the immune function of hemocytes in the mussel Mytilus coruscus.

Numerous studies have shown that microplastics can interact with other pollutants in the environment to produce synergistic effects, leading to more serious impacts. To date, there is little consensus on the combined effects of microfibers (MFs) and polychlorinated biphenyls (PCBs, Aroclor 1254), two legacy and alarming environmental pollutants. There is an urgent need to assess the impact of combined exposures on bivalve immune defences. In this study, we assessed the immune response of the mussels (Mytilus coruscus) hemocyte to MFs and PCBs alone and in combination by using flow cytometry. M. coruscus were exposed to MFs (1000 pieces/L) and PCBs (PCBs) (100 ng/L and 1000 ng/L) alone or in combination for 14 consecutive days and recovered for 7 days. The hemocyte of M. coruscus was collected on day 7, 14 and 21. MF exposure alone had no effect on the hemocyte. The total hemocyte count (THC), esterase (EA), lysosomal contents (LC), mitochondrial number (MN) and mitochondrial membrane potential (MMP) of mussels showed a decreasing trend with increasing PCB concentrations, both individually and in combination; The decreases in EA, MN and MMP were associated with the induction of reactive oxygen species (ROS). Hemocyte mortality (HM) was associated with a decrease in THC. Combined exposure to MFs and PCBs would exacerbate the effects on hemocyte immunity. These new findings improve our understanding of the toxic effects of MFs and organic chemical pollutants, and demonstrate the potential mechanism of PCBs to bivalves through changes in hemolymph immunity-related indicators.

Nano-TiO2 aggravates the adverse effect of pentachlorophenol on antioxidant and immune response in anti-predatory mussels.

Nano-TiO2 can act as a vector to organic compounds, such as pentachlorophenol (PCP) posing a potential threat to the marine ecosystems. Studies showed that nano pollutant toxicity can be modulated by abiotic factors, but little is known about the potential influence of biotic stressors (such as predators) on the physiological responses to pollutants in marine organisms. We explored the effects of n-TiO2 and PCP on the mussel Mytilus coruscus in the presence of its natural predator, the swimming crab Portunus trituberculatus. Exposure to n-TiO2, PCP, and predation risk showed interactive effects on antioxidant and immune parameters of the mussels. Elevated activities of catalase (CAT), glutathione peroxidase (GPX), acid phosphatase (ACP) and alkaline phosphatase (AKP), suppressed activity of superoxide dismutase (SOD), lower levels of glutathione (GSH) and increased malondialdehyde (MDA) levels indicated dysregulation of the antioxidant system and immune stress induced by single PCP or n-TiO2 exposure. Integrated biomarker (IBR) response values showed the effect of PCP was concentration dependent. Of the two used n-TiO2 sizes (25 and 100 nm), larger particles induced higher antioxidant and immune disturbances indicating higher toxicity possibly due to higher bioavailability. Compared to single PCP exposure, the combination of n-TiO2 and PCP enhanced the imbalance of SOD/CAT and GSH/GPX and led to elevated oxidative lesions and activation of immune-related enzymes. Overall, the combined impacts of pollutants and biotic stress exhibited a greater magnitude of adverse effects on antioxidant defense and immune parameters in mussels. The toxicological effects of PCP were exacerbated in the presence of n-TiO2, and the deleterious impact of these stressors was further amplified under predator-induced risk after prolonged (28 days) exposure. However, the underlying physiological regulatory mechanisms governing the interplay of these stressors and predatory cues on mussels remain elusive, warranting further investigation.

Intestinal response of mussels to nano-TiO2 and pentachlorophenol in the presence of predator.

With the development of industry, agriculture and intensification of human activities, a large amount of nano-TiO2 dioxide and pentachlorophenol have entered aquatic environment, causing potential impacts on the health of aquatic animals and ecosystems. We investigated the effects of predators, pentachlorophenol (PCP) and nano titanium dioxide (nano-TiO2) on the gut health (microbiota and digestive enzymes) of the thick-shelled mussel Mytilus coruscus. Nano-TiO2, as the photocatalyst for PCP, enhanced to toxic effects of PCP on the intestinal health of mussels, and they made the mussels more vulnerable to the stress from predators. Nano-TiO2 particles with smaller size exerted a larger negative effect on digestive enzymes, whereas the size effect on gut bacteria was insignificant. The presence of every two of the three factors significantly affected the population richness and diversity of gut microbiota. Our findings revealed that the presence of predators, PCP, and nano-TiO2 promoted the proliferation of pathogenic bacteria and inhibited digestive enzyme activity. This research investigated the combined stress on marine mussels caused by nanoparticles and pesticides in the presence of predators and established a theoretical framework for explaining the adaptive mechanisms in gut microbes and the link between digestive enzymes and gut microbiota.

Microplastics and food shortage impair the byssal attachment of thick-shelled mussel Mytilus coruscus.

Microplastics (MPs) have become a ubiquitous emerging pollutant in the global marine environment. The potential toxic effects of MPs and interactions of MP pollution with other stressors such as food limitation on marine organisms' health are not yet well understood. This study investigated the effects of three-week exposure to different MPs and food shortage on the physical defense mechanisms (byssus production and properties) of Mytilus coruscus. Starvation significantly reduced the number of byssus threads, and combined exposure to MPs and food shortage suppressed the adhesion ability and condition index of mussels. The length of the byssus threads was not affected by all experimental exposures. Transcript levels of genes encoding key proteins involved in byssus formation (the mussel foot proteins mfp-1, -2, -3, -4, -5 and -6, and prepolymerized collagen proteins preCOL-D, -P and -NG) were altered by interactions between the MPs and food shortage. These findings show that insufficient food supply can exacerbate the adverse effects of MPs on mussel defense which might have implications for survival and fitness of mussels under food limited conditions (e.g. in winter) in polluted coastal habitats.

Enhanced immunity and hemocytes proliferation by three immunostimulants in tri-spine horseshoe crab Tachypleus tridentatus.

Tachypleus amebocyte lysate (TAL) is crucial in medical testing, but its industry in China has been restricted due to the decline of horseshoe crab population in recent years. Exploring methods of enhancing immunity and rapid hemocytes proliferation is urgent for the industrial horseshoe crab culture. In this study, ß-glucan (G), peptidoglycan (P), and squalene (S) were injected to horseshoe crabs at two concentrations (5 and 10 mg/kg), in order to compare their effects on total hemocyte count (THC), reactive oxygen species (ROS), and non-specific immune enzyme activities. Results showed that the THC, superoxide dismutase (SOD), catalase (CAT), and total antioxidant capacity (T-AOC) were significantly increased by three immunostimulants at different points of time; ROS was significantly increased except at two squalene groups; lysozyme (LZM) and alkaline phosphatase (AKP) activity were increased except at low dose (5 mg/kg) squalene group; malondialdehyde (MDA) activity was decreased in all treatments; and hemocyanin concentration (HC) changed little during the experiment. At the 48th hour, THC, ROS, SOD, CAT, T-AOC, LZM, and AKP activities were significantly higher in the two peptidoglycan groups than those in the control group; the low dose ß-glucan and squalene groups showed significantly higher SOD and CAT, but their THC and AKP were not significantly different from those of the control group. In general, all three immunostimulants stimulated the hemolymph parameters of horseshoe crabs, notably, peptidoglycan could significantly increase the THC and enzyme activities, suggesting that peptidoglycan can be developed as an efficient immunostimulant for horseshoe crabs.

Understanding plastic degradation and microplastic formation in the environment: A review.

Plastic waste are introduced into the environment inevitably and their exposure in the environment causes deterioration in mechanical and physicochemical properties and leads to the formation of plastic fragments, which are considered as microplastics when their size is < 5 mm. In recent years, microplastic pollution has been reported in all kinds of environments worldwide and is considered a potential threat to the health of ecosystems and humans. However, knowledge on the environmental degradation of plastics and the formation of microplastics is still limited. In this review, potential hotspots for the accumulation of plastic waste were identified, major mechanisms and characterization methods of plastic degradation were summarized, and studies on the environmental degradation of plastics were evaluated. Future research works should further identify the key environmental parameters and properties of plastics affecting the degradation in order to predict the fate of plastics in different environments and facilitate the development of technologies for reducing plastic pollution. Formation and degradation of microplastics, including nanoplastics, should receive more research attention to assess their fate and ecological risks in the environment more comprehensively.

Impact of particulate sediment, bentonite and barite (oil-drilling waste) on net fluxes of oxygen and nitrogen in Arctic-boreal sponges.

To meet the increasing global energy demand, expanding exploration for oil and gas reserves as well as associated drilling activities are expected in the Arctic-boreal region where sponge aggregations contribute to up to 90% of benthic biomass. These deep-water sponges along with their microbial endobionts play key roles in the nitrogen cycling in Arctic-boreal ecosystems. This study aimed to investigate the effects of drilling discharges and associated sediment resuspension events on net fluxes of oxygen, ammonium, nitrate and nitrite in three common deep-water sponge species in the form of explants. Sponges were exposed to suspended bentonite and barite, the primary particulate compounds in drilling waste, as well as suspended natural sediment particles for a period of 33 days (on average 10 mg L-1 for 12 h day-1). The exposure period was followed by a pollution abatement period for a further 33 days. No sponge mortality was observed during the experiment. However, exposure to these particles, especially to barite, led to reduced oxygen consumption by up to 33% that was linearly correlated with reduced nitrite/nitrate release by the sponges. The changes in net fluxes were accompanied by decreased tissue oxygenation by up to 54% within the sponges. These findings reveal the effects of fine particles on sponge metabolic processes by reducing aerobic respiration and microbial nitrification, and possibly by favouring anaerobic processes such as microbial denitrification. Most of the sponge responses recovered to their control levels upon the pollution abatement period, but the effects caused by barite may not be reversible. Our findings provide the first insight into the ecological consequences of oil and gas drilling activities on sponge-mediated nitrogen cycling in the Arctic-boreal region.

Bleaching and mortality of a photosymbiotic bioeroding sponge under future carbon dioxide emission scenarios.

The bioeroding sponge Cliona orientalis is photosymbiotic with dinoflagellates of the genus Symbiodinium and is pervasive on the Great Barrier Reef. We investigated how C. orientalis responded to past and future ocean conditions in a simulated community setting. The experiment lasted over an Austral summer under four carbon dioxide emission scenarios: a pre-industrial scenario (PI), a present-day scenario (PD; control), and two future scenarios of combined ocean acidification and ocean warming, i.e., B1 (intermediate) and A1FI (extreme). The four scenarios also simulated natural variability of carbon dioxide partial pressure and temperature in seawater. Responses of C. orientalis generally remained similar between the PI and PD treatments. C. orientalis under B1 displayed a dramatic increase in lateral tissue extension, but bleached and displayed reduced rates of respiration and photosynthesis. Some B1 sponge replicates died by the end of the experiment. Under A1FI, strong bleaching and subsequent mortality of all C. orientalis replicates occurred at an early stage of the experiment. Mortality arrested bioerosion by C. orientalis under B1 and A1FI. Overall, the absolute amount of calcium carbonate eroded by C. orientalis under B1 or A1FI was similar to that under PI or PD at the end of the experiment. Although bioerosion rates were raised by short-term experimental acidification in previous studies, our findings from the photosymbiotic C. orientalis imply that the effects of bioerosion on reef carbonate budgets may only be temporary if the bioeroders cannot survive long-term in the future oceans.

Sponge bioerosion on changing reefs: ocean warming poses physiological constraints to the success of a photosymbiotic excavating sponge.

Excavating sponges are prominent bioeroders on coral reefs that in comparison to other benthic organisms may suffer less or may even benefit from warmer, more acidic and more eutrophic waters. Here, the photosymbiotic excavating sponge Cliona orientalis from the Great Barrier Reef was subjected to a prolonged simulation of both global and local environmental change: future seawater temperature, partial pressure of carbon dioxide (as for 2100 summer conditions under "business-as-usual" emissions), and diet supplementation with particulate organics. The individual and combined effects of the three factors on the bioerosion rates, metabolic oxygen and carbon flux, biomass change and survival of the sponge were monitored over the height of summer. Diet supplementation accelerated bioerosion rates. Acidification alone did not have a strong effect on total bioerosion or survival rates, yet it co-occurred with reduced heterotrophy. Warming above 30 °C (+2.7 °C above the local maximum monthly mean) caused extensive bleaching, lower bioerosion, and prevailing mortality, overriding the other factors and suggesting a strong metabolic dependence of the sponge on its resident symbionts. The growth, bioerosion capacity and likelihood of survival of C. orientalis and similar photosymbiotic excavating sponges could be substantially reduced rather than increased on end-of-the-century reefs under "business-as-usual" emission profiles.

Effects of ocean warming and acidification on the energy budget of an excavating sponge.

Recent research efforts have demonstrated increased bioerosion rates under experimentally elevated partial pressures of seawater carbon dioxide (pCO2 ) with or without increased temperatures, which may lead to net erosion on coral reefs in the future. However, this conclusion clearly depends on the ability of the investigated bioeroding organisms to survive and grow in the warmer and more acidic future environments, which remains unexplored. The excavating sponge Cliona orientalis Thiele, is a widely distributed bioeroding organism and symbiotic with dinoflagellates of the genus Symbiodinium. Using C. orientalis, an energy budget model was developed to calculate amounts of carbon directed into metabolic maintenance and growth. This model was tested under a range of CO2 emission scenarios (temperature + pCO2 ) appropriate to an Austral early summer. Under a pre-industrial scenario, present day (control) scenario, or B1 future scenario (associated with reducing the rate of CO2 emissions over the next few decades), C. orientalis maintained a positive energy budget, where metabolic demand was likely satisfied by autotrophic carbon provided by Symbiodinium and heterotrophic carbon via filter-feeding, suggesting sustainability. Under B1, C. orientalis likely benefited by a greater supply of photosynthetic products from its symbionts, which increased by up to 56% per unit area, and displayed an improved condition with up to 52% increased surplus carbon available for growth. Under an A1FI future scenario (associated with 'business-as-usual' CO2 emissions) bleached C. orientalis experienced the highest metabolic demand, but carbon acquired was insufficient to maintain the sponge, as indicated by a negative energy budget. These metabolic considerations suggest that previous observations of increased bioerosion under A1FI by C. orientalis may not last through the height of future A1FI summers, and survival of individual sponges may be dependent on the energy reserves (biomass) they have accumulated through the rest of the year.

Sponge biomass and bioerosion rates increase under ocean warming and acidification.

The combination of ocean warming and acidification as a result of increasing atmospheric carbon dioxide (CO2 ) is considered to be a significant threat to calcifying organisms and their activities on coral reefs. How these global changes impact the important roles of decalcifying organisms (bioeroders) in the regulation of carbonate budgets, however, is less understood. To address this important question, the effects of a range of past, present and future CO2 emission scenarios (temperature + acidification) on the excavating sponge Cliona orientalis Thiele, 1900 were explored over 12 weeks in early summer on the southern Great Barrier Reef. C. orientalis is a widely distributed bioeroder on many reefs, and hosts symbiotic dinoflagellates of the genus Symbiodinium. Our results showed that biomass production and bioerosion rates of C. orientalis were similar under a pre-industrial scenario and a present day (control) scenario. Symbiodinium population density in the sponge tissue was the highest under the pre-industrial scenario, and decreased towards the two future scenarios with sponge replicates under the 'business-as-usual' CO2 emission scenario exhibiting strong bleaching. Despite these changes, biomass production and the ability of the sponge to erode coral carbonate materials both increased under the future scenarios. Our study suggests that C. orientalis will likely grow faster and have higher bioerosion rates in a high CO2 future than at present, even with significant bleaching. Assuming that our findings hold for excavating sponges in general, increased sponge biomass coupled with accelerated bioerosion may push coral reefs towards net erosion and negative carbonate budgets in the future.

Ethoxyresorufin-O-deethylase enzyme activities and accumulation of secondary/tertiary lysosomes in rabbitfish Siganus oramin as biomarkers for xenobiotic exposures.

The sensitivities of using hepatic and intestinal ethoxyresorufin-O-deethylase (EROD) activities and hepatic accumulation of secondary/tertiary (2 degrees/3 degrees) lysosomes to detect xenobiotic exposures were assessed in the rabbitfish Siganus oramin in a metropolitan harbour, subtropical Hong Kong, over a complete seasonal cycle of one year. Additional information on the body-burden pollutants and physiological indices in S. oramin, and seasonal variables in seawater quality, were extracted from published data and re-analyzed. Under the influences of pollutant cocktail and seasonal factors, neither the hepatic nor intestinal EROD activity was indicative of total polycyclic aromatic hydrocarbons (Sigma PAH), total polychlorinated biphenyls, condition factor and hepatosomatic index (HSI) in S. oramin. However, the relative ratio of hepatic to intestinal EROD activities provided an indication to differentiate the xenobiotic intake route in the fish through diffusion via gills/skin or consumption of contaminated food. In addition, the elevated hepatic accumulation of 2 degrees/3 degrees lysosomes was closely associated with the dominant temporal trends of zinc and Sigma PAH, as well as reduced HSI, in S. oramin. Being minimally influenced by any investigated seasonal factors, the hepatic 2 degrees/3 degrees lysosomes in S. oramin was recommended as an effective biomarker of xenobiotic exposures and toxic effects for use in coastal pollution monitoring programmes.

Seasonality of bioaccumulation of trace organics and lysosomal integrity in green-lipped mussel Perna viridis.

Lysosomal integrity in mussels is widely used as a biomarker in coastal environments to demonstrate exposure to trace organic pollutants. However, few studies have determined the long-term influences of seasonal variations on the bioaccumulation of trace organics and subsequently altered response of lysosomal integrity in mussels. This study aimed to test three null hypotheses that (1) bioaccumulations of total polycyclic aromatic hydrocarbon (SigmaPAH) and (2) total polychlorinated biphenyl (SigmaPCB), and (3) lysosomal integrity as indicated by Neutral Red retention time (NRRT) in haemocytes, in the green-lipped mussel Perna viridis were not seasonally dependent. The tissue concentrations of SigmaPAH and SigmaPCB and haemocytic NRRT were determined in P. viridis in a metropolitan harbour, subtropical Hong Kong during the wet and dry seasons from 2004 to 2007. Additional information on temperature, salinity, dissolved oxygen and total ammonia nitrogen in seawater, and sediment levels of SigmaPAH and SigmaPCB, were extracted from published data and re-analyzed. Our results accepted all null hypotheses, based on the minimal seasonal influences of seawater temperature and salinity on all studied parameters, in which no significant differences between the wet and dry seasons were detected. The seasonal effect was likely outweighed by the greatly improved water quality and pollution abatement noted inside the harbour, with a gradual shift in mussel PAHs from a pyrolytic origin to a petrogenic origin. Spatially, the site east of the harbour was relatively unpolluted. The single use of NRRT in P. viridis explained 25% of the total variation of the integrated pollution patterns in seawater, sediments and mussels. The present study suggested that the dynamic change of trace organics could be reflected by the response on lysosomal integrity in P. viridis, which was recommended as a routine screening biomarker in monitoring of harbour water quality across seasons.

The use of muscle burden in rabbitfish Siganus oramin for monitoring polycyclic aromatic hydrocarbons and polychlorinated biphenyls in Victoria Harbour, Hong Kong and potential human health risk.

Muscle concentrations of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were determined in rabbitfish Siganus oramin collected from Victoria Harbour and its vicinity, Hong Kong from 2004 to 2007. Spatially, relatively higher levels of [summation operator]PAH (1.05-4.26 microg g(-1)) and [summation operator]PCB (45.1-76.9 ng g(-1)) were determined in the central and western sites inside the harbour. Temporally, upward trend of [summation operator]PAH, accompanied with a proportion shift from high molecular weight to low molecular weight PAHs, was detected during the three-year study period, suggesting a heavier marine traffic in Victoria Harbour and its western region. However, human health risk assessment based on five individual PAHs indicated that PAHs in fish muscles posed minimal health risk through consumption. In contrast, a downward trend of [summation operator]PCB was registered as the open use of PCBs has been banned. Despite this, the level of [summation operator]PCB in fish muscles still posed a health risk on the local people who have a high fish consumption rate. While seasonal influences on [summation operator]PAH/[summation operator]PCB accumulation in S. oramin seemed to be negligible, our findings in S. oramin were in line with the established PAH and PCB levels in sediments and/or mussels from the harbour, suggesting S. oramin can be used as a model fish species for monitoring PAHs and PCBs in the region.

Measuring and monitoring persistent organic pollutants in the context of risk assessment.

Due to growing concerns regarding persistent organic pollutants (POPs) in the environment, extensive studies and monitoring programs have been carried out in the last two decades to determine their concentrations in water, sediment, and more recently, in biota. An extensive review and analysis of the existing literature shows that whilst the vast majority of these efforts either attempt to compare (a) spatial changes (to identify "hot spots"), or (b) temporal changes to detect deterioration/improvement occurring in the environment, most studies could not provide sufficient statistical power to estimate concentrations of POPs in the environment and detect spatial and temporal changes. Despite various national POPs standards having been established, there has been a surprising paucity of emphasis in establishing accurate threshold concentrations that indicate potential significant threats to ecosystems and public health. Although most monitoring programs attempt to check compliance through reference to certain "environmental quality objectives", it should be pointed out that many of these established standards are typically associated with a large degree of uncertainty and rely on a large number of assumptions, some of which may be arbitrary. Non-compliance should trigger concern, so that the problem can be tracked down and rectified, but non-compliance must not be interpreted in a simplistic and mechanical way. Contaminants occurring in the physical environment may not necessarily be biologically available, and even when they are bioavailable, they may not necessarily elicit adverse biological effects at the individual or population levels. As such, we here argue that routine monitoring and reporting of abiotic and biotic POPs concentrations could be of limited use, unless such data can be related directly to the assessment of public health and ecological risks. Risk can be inferred from the ratio of predicted environmental concentration (PEC) and the predicted no effect concentration (PNEC). Currently, the paucity of data does not allow accurate estimation of PNEC, and future endeavors should therefore, be devoted to determine the threshold concentrations of POPs that can cause undesirable biological effects on sensitive receivers and important biological components in the receiving environment (e.g. keystone species, populations with high energy flow values, etc.), to enable derivation of PNECs based on solid scientific evidence and reduce uncertainty. Using the threshold body burden of POPs required to elicit damages of lysosomal integrity in the green mussel (Perna virvidis) as an example, we illustrate how measurement of POPs in body tissue could be used in predicting environmental risk in a meaningful way.