Detoxification mechanisms in shrimp: comparative approach between hydrothermal vent fields and estuarine environments

Hydrothermal vents are extreme deep-sea habitats that, due to their singular features, still intrigue scientific communities. Swift growth rates and profuse biomass of biological communities can be observed, despite of their inherently unstable physical-chemical and toxic conditions, indicating that organisms inhabiting this environment must be well adapted to these inhospitable conditions. The caridean shrimp, Chorocaris chacei, Mirocaris fortunata and Rimicaris exoculata, together with bathymodiolid mussels, dominate the vent fauna along the Mid-Atlantic Ridge (MAR). Crustacean species are widely used as biological indicators of environmental alterations, since they play a key ecological role as planktivorous grazers, epibenthic scavengers or as prey species. The biological consequences of the hydrothermal metal-rich environment in shrimp species are still largely unknown. Therefore, the aim of this study was the determination of the metal levels (Ag, Cd, Cu, Fe, Mn and Zn), metallothioneins (MT) and lipid peroxidation (LPO) in shrimp species collected in Rainbow, Lucky Strike and Menez-Gwen vent sites, in order to evaluate their different adaptation strategies toward metals when compared with two common coastal shrimp species (Palaemon elegans and Palaemonetes varians) from a fairly unpolluted estuarine system in south Portugal (Ria Formosa). Results show significant differences in metal concentrations, MT levels and lipid peroxidation between vent and coastal shrimp and also between shrimp species from the same site. This indicates that biochemical responses in both vent and coastal shrimp are affected not only by the environmental characteristics but also by inter-specific differences. Nevertheless, these responses apparently grant a successful adaptation for the survival in a metal-extreme environment.     

Hydrothermal vent meiobenthos associated with mytilid mussel aggregations from the Mid-Atlantic Ridge and the East Pacific Rise

Deep-sea hydrothermal vents occur along the mid-ocean ridges and back-arc basins around the globe. There are very few community analyses of vent meiobenthos. The central objectives of this study were to identify and quantify for the first time the entire metazoan meiobenthic community associated with mussel aggregations of Bathymodiolus thermophilus Kenk and Wilson, 1985 from the EPR, 11°N and of Bathymodiolus puteoserpentis Cosel et al., 1994 from the Mid-Atlantic Ridge (MAR), 23°N. Using a quantitative sampling method, abundance, biomass, sex ratio, species richness, diversity, evenness, and trophic structure were studied based on three samples from each site. Meiobenthic abundance in each sample was unexpectedly low, but similar between sites. The community was composed of nematodes, copepods, ostracods, and mites, with a total of 24 species at EPR vents, and 15 species at MAR vents. While most copepod species were vent endemics within the family Dirivultidae, nematodes and harpacticoid copepods belonged to generalist genera, which occur at a variety of habitats and are not restricted to hydrothermal vents or the deep sea. The meiobenthos of hydrothermal-vent mussel beds constitutes a unique community unlike those of other sulfidic habitats, including the thiobios of shallow-water sediments and the meiobenthos of deep-sea, cold-seep sediments. The trophic structure was dominated by primary consumers, mainly deposit feeders, followed by parasites. Predatory meiofaunal species were absent.     

Spatial distribution, diversity and composition of bacterial communities in sub-seafloor fluids at a deep-sea hydrothermal field of the Suiyo Seamount

Spatial distribution, diversity, and composition of bacterial communities within the shallow sub-seafloor at the deep-sea hydrothermal field of the Suiyo Seamount, Izu-Bonin Arc, Western Pacific Ocean, were investigated. Fluids were sampled from four boreholes in this area. Each borehole was located near or away from active vents, the distance ranging 2–40 m from active vents. In addition, fluids discharging from a natural vent and ambient seawater were sampled in this area. We extracted DNA from each sample, amplified bacterial 16S rRNA genes by PCR, cloned the PCR products and sequenced. The total number of clones analyzed was 348. Most of the detected phylotypes were affiliated with the phylum Proteobacteria, of which the detection frequency in each clone library ranged from 84.6% to 100%. The bacterial community diversity and composition were different between hydrothermal fluids and seawater, between fluids from the boreholes and the vent, and even among fluids from each borehole. The relative abundances of the phylotypes related to Thiomicrospira, Methylobacterium and Sphingomonas were significantly different among fluids from each borehole. The phylotypes related to Thiomicrospira and Alcanivorax were detected in all of the boreholes and vent samples. Our findings provide insights into bacterial communities in the shallow sub-seafloor environments at active deep-sea hydrothermal vent fields.     

Bioaccumulation des métaux chez le mytilidae hydrothermal Bathymodiolus sp. de la ride médio-atlantique

The hydrothermal environment is characterised, among other things, by a high metal concentration, related to the convective sea-water circulation inside the oceanic crust and its interaction with basaltic rocks. The biological communities associated with the hydrothermal system can survive in this toxic environment owing to their ability to regulate their intracellular metal levels by excretion or accumulation of metal ions in non-toxic forms. Various detoxification processes have been previously studied within an hydrothermal organism: immobilisation and precipitation of the metal in lysosomal systems, or binding to specific and soluble ligands such as metallothioneins. The later are heat stable and characterised by a high content of cysteine. The quantification of Fe, Zn, Cu, Mn, Cd, Ag, Ba and Sr in the tissues of the vent mussel Bathymodiolus sp. indicates a high accumulation of these metals in two target organs, the gill and the digestive gland. This accumulation is in relation with high concentrations of metallothioneins, but the subcellular distribution of metals indicates a higher contribution of the insoluble compartment for detoxification processes. These results are compared with the literature data about metal bioaccumlation in Bathymodiolus thermophilus collected at the Galapagos Rift.     

Spatial variation of metal bioaccumulation in the hydrothermal vent mussel Bathymodiolus azoricus

The variability of the bioaccumulation of metals (Ag, Cd, Cu, Fe, Mn and Zn) was extensively studied in the mussel Bathymodiolus azoricus from five hydrothermal vent sites inside three main vent fields of increasing depth along the Mid-Atlantic Ridge: Menez Gwen, Lucky Strike and Rainbow. Metal bioaccumulation varied greatly between vent fields and even between sites inside a vent field with B. azoricus showing a great capacity to accumulate metals. The bioaccumulation of these metals also varied significantly among tissues. The main target was the gills where metals were mainly associated with soluble compounds whereas in the digestive gland they were mainly associated with insoluble compounds. Storage of metals under insoluble forms in B. azoricus seems to be a major pathway for the detoxification of both essential and non-essential metals. Mussels from the studied fields can be discriminated following their metallic load but the segregation relies partially on the composition of the metal-enriched fluids.     

Patterns of Gene Expression Variation across Body Parts of the Hydrothermal Vent Shrimp Nautilocaris saintlaurentae

Ocean Science Journal - Since deep-sea hydrothermal vents have been targeted for mining mineral resources, concerns about the potential impacts of mining on vent ecosystems have gradually...     

Relationship between metal levels in the vent mussel Bathymodiolus azoricus and local microhabitat chemical characteristics of Eiffel Tower (Lucky Strike)

The turbulent mixing of hydrothermal hot fluid with cold seawater creates large chemical gradients at a small spatial scale that may induce variable physiological and biochemical adaptations within the vent fauna. The adaptation to such a variable environment by the vent mussel Bathymodiolus azoricus relies on a dual symbiosis hosted in the gills, and digestion of particulate organic matter. The surrounding environment not only provides the necessary energy sources and suspended organic particles for the vent mussel nutrition, but also potentially toxic compounds such as metals. Our main goal was to see if there is a relation between metal accumulation in mussel organs and the chemical characteristics of their close environment. Mussels were collected at six locations in a cold part of the Eiffel Tower fluid-seawater mixing zone, characterized by distinct chemical compositions. Metals (Cd, Cu, Fe and Zn) and metallothioneins were quantified in the gills and digestive gland. The physiological condition of the sampled mussels was also evaluated using tissues and gill indices. Our study indicates that the accumulation of metals in B. azoricus is related to their spatial distribution and linked to fine scale environmental conditions that influence the physiological status of the organism.     

Microbial Diversity of Deep-sea Sediments from Three Newly Discovered Hydrothermal Vent Fields in the Central Indian Ridge

Since the discovery of hydrothermal vents in the late 1970s, deep-sea hydrothermal vent fields have attracted great attention as biological hotspots. However, compared with other ocean ridges, the structure and function of microbial communities inhabiting vent fields in the Central Indian ridge (CIR) remain understudied. Here, we provide for the first time 16S rRNA gene-based comparative metagenomic analysis of the sediment-associated microbial communities from three newly discovered vent fields in the CIR. Sediment samples collected in the Invent B, Invent E and Onnuri vent fields varied in geochemical properties, elemental concentrations and associated microbial communities. Proteobacteria (Gammaproteobacteria) was the dominant phylum in Invent B and Onnuri vent fields. In contrast, Invent E mainly consisted of Chloroflexi and Euryarchaeota. Predicted functional profiling revealed that the microbial communities in the three vents are dominated by chemoheterotrophic functions. In addition, microbial communities capable of respiration of sulfur compounds, nitrification, nitrite oxidation, methylotrophy, and methanotropy were found to be the main chemolithoautotrophs. Compared to other vent fields, Invent E showed a predominance of archaeal methanogens suggesting it exhibits slightly different geochemistry. Multivariate analysis indicated that the biogeochemical and trace metal differences are reflected in the sediment microbial compositions of the three vent fields. This study expands our current understanding of the microbial community structure and potential ecological functions of the newly discovered hydrothermal vent fields in the CIR.

     

Adaptation of the antioxidant defence system in hydrothermal-vent mussels (Bathymodiolus azoricus) transplanted between two Mid-Atlantic Ridge sites

The vent mussel Bathymodiolus azoricus is the dominant member of the Northern Mid‐Atlantic Ridge (MAR) hydrothermal megafauna, and lives in an environment characterized by temporal and spatial variations in the levels of heavy metals, methane and hydrogen sulphide, substances which are known to increase reactive oxygen species levels in the tissues of exposed organisms. To evaluate the effects of two contrasting hydrothermal environments on the antioxidant defence system of this vent mussel species, a 2‐week transplant experiment was carried out involving mussels collected from the relatively deep (2300 m), and chemical rich, Rainbow vent field. These were transplanted to the shallower (1700 m), and relatively less toxic, Lucky Strike vent field. To achieve this objective, levels of superoxide dismutase, catalase (CAT), total glutathione peroxidase (GPx), selenium‐dependent glutathione peroxidase and lipid peroxidation (LPO) were measured in the gills and mantle tissues of resident and transplant mussels before and after the transplant experiment. With the exception of CAT, the gills of the transplanted mussels had significantly higher antioxidant enzyme activity compared with the basal levels in the donor (Rainbow) and recipient (Lucky Strike) populations; whereas the antioxidant enzyme levels in the mantle tissues of the transplants reflected the baseline levels of activity in the native Lucky Strike mussels after 2 weeks. In contrast, LPO levels were significantly higher in both tissue types in the transplants than in either the source or the recipient populations, which suggested a response to hydrostatic pressure change (note, the transplant animals were brought to the surface for transportation between the two vent fields). The fact that the Rainbow mussels survived the transplant experience indicates that B. azoricus has a very robust constitution, which enables it to cope behaviourally, physiologically and genetically with the extreme conditions found in its naturally contaminated deep‐sea environment.     

Regulation of Tilapia metallothionein gene expression by heavy metal ions

Tilapia is a common fish species inhabiting inland waters and estuarine regions in Hong Kong and Southeast Asia, and useful for bio-monitoring of metal pollution. Metallothionein (MT) gene expression in fish tissues has been useful to sub-lethal risk assessment as biomarker of exposure to metal ions in fishes inhabiting metal contaminated area. To investigate metal inductions of Tilapia MT gene expression in vivo, Tilapias were injected with different concentrations of heavy metals and tissues were then removed for quantitative PCR assay using mimic PCR methods. All of the metal ions tested (Cu(2+), Cd(2+), Hg(2+), Ni(2+), Pb(2+) and Zn(2+)) were able to induce hepatic MT mRNA levels. Renal MT mRNA levels of Cd(2+) and Zn(2+) treated fish was not induced with significant fold induction, however MT mRNA levels in gills were sensitive to the administrations of these metal ions. These data indicated that Tilapia MT mRNA levels in gills and liver are sensitive biomarker of exposure to various metal ions.     

Adaptation to metal toxicity: a comparison of hydrothermal vent and coastal shrimps

Rainbow vent field is one of the most metal‐contaminated hydrothermal sites on the Mid‐Atlantic Ridge near the Azores region. Two hydrothermal shrimp species dominate the fauna at the Rainbow site along with the mussel Bathymodiolus azoricus. Although the levels of essential and non‐essential metals in these shrimps have been studied, the biological consequences of a metal‐rich environment are still largely unknown. Therefore, the aim of this study was to determine the levels of metal‐binding proteins – metallothioneins (MT) and the activities of antioxidant enzymes – superoxide dismutase, catalase, total glutathione peroxidase and selenium‐dependent glutathione peroxidase in two hydrothermal vent shrimps (Mirocaris fortunata and Rimicaris exoculata) collected from the Rainbow site and to compare them with two coastal shrimps (Palaemon elegans and Palaemonetes varians) from a south Portugal lagoon (Ria Formosa) to evaluate their different adaptation strategies towards metals in their environment. Results show significant differences in MT levels and antioxidant enzymatic activities between vent and coastal shrimps and also between shrimp species collected from the same site. This suggests that biochemical responses in both vent and coastal shrimps are affected not only by the environmental characteristics but also by inter‐specific differences. Nevertheless, these responses apparently confer successful adaptation for survival in a metal‐extreme environment.     

软体动物腹足纲分类学研究进展——从近海到深海

随着科学技术的不断进步和研究的不断深入,我国关于海洋的研究已由浅海逐步向深海发展,不断取得新的发现和认知。自2014年4月起,中国科学院海洋研究所依托先进的"科学"号海洋科学综合考察船,搭载"发现"号水下机器人（remotelyoperated vehicle,ROV）,先后对冲绳海槽热液区、南海冷泉区、雅浦海山区以及马努斯热液区等深海区域进行了综合性科学考查,采集到了大量深海腹足纲（Gastropoda）标本,其中有一些为未经发现和描述的新种,极大地推动了我国关于深海软体动物物种多样性研究,实现了深海环境和软体动物资源的新认知。本文对近年来从深海采集到的腹足类标本进行了整理分类,对其中的11属13种进行描述,并对深海特殊环境中腹足纲物种多样性进行了总结,对中国软体动物腹足纲从近海至深海的分类现状进行研究论述。     

Concentrations of heavy metals in marine wild fishes captured from the southern sea of Korea and associated health risk assessments

Concentrations of heavy metals (As, Cd, Cr, Cu, Hg, Pb, and Zn) were determined in edible parts (muscle) of 34 marine wild fish caught from the southern sea of Korea in 2007 and 2008 in order to understand the accumulation pattern of heavy metals in wild fish and to assess the potential health risk posed by fish consumption. The highest concentrations in the muscle of 17 pelagic and 17 demersal fishes were Zn and As, respectively, while the lowest concentration in both fishes was Cd. The mean concentrations of all metals except As in wild fish were much lower than the regulatory limits for fish and fishery products applied in a number of countries. Unlike other metals, As concentration in wild fish of this study region was relatively higher than that found in other country. Estimated daily intake (EDI) of the metals was in the range of 0.05% to 22.5% of the provisional maximum tolerable daily intakes (PMTDI). Similarly, the target hazard quotient (THQ) was below 1.0 for each metal. These results imply that the consumption of the investigated wild fish do not cause significant adverse health effects.     

Temporal variation in the antioxidant defence system and lipid peroxidation in the gills and mantle of hydrothermal vent mussel Bathymodiolus azoricus

Hydrothermal vent mussels are exposed continually to toxic compounds, including high metal concentrations and other substances like dissolved sulphide, methane and natural radioactivity. Fluctuations in these parameters appear to be common because of the characteristic instability of the hydrothermal environment. Temporal variation in the antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), total glutathione peroxidases (Total GPx), selenium dependent glutathione peroxidases (Se-GPx)), metallothioneins and lipid peroxidation (LPO) in the gills and mantle of the mussel Bathymodiolus azoricus from Menez–Gwen hydrothermal vent site was evaluated and related to the accumulated metal concentrations (Ag, Cu, Cd, Fe, Mn and Zn) in the tissues. Maximum antioxidant enzyme activities in the gills were detected in the beginning of summer, followed by a gradual decrease throughout the following months. One year after, the levels of antioxidant enzyme activities were similar to those reported one year before. LPO in this tissue exhibited a similar temporal variation trend. A different pattern of temporal variation in antioxidant enzyme activities was observed in the mantle, with a gradual increase from summer to the end of autumn (November). LPO in the mantle exhibited an almost reverse trend of temporal variation to that of antioxidant enzyme activities in this tissue. Antioxidant defences in the gills of B. azoricus were significantly enhanced with increasing concentrations of Ag, Cu and Mn, while negative relationships between antioxidant enzymes and Cd, Cu, Mn and Zn concentrations in the mantle were observed, suggesting different pathways of reactive oxygen species (ROS) production and that these tissues responded differently to the metal accumulation. However, temporal variation in biomarkers of defence and damage were in general similar to coastal bivalve species and can be associated with temporal variations of the physiological status due to reproduction. These variations might also be linked to the highly unstable nature of the hydrothermal environment.     

A data processing method for MAPR hydrothermal plume turbidity data and its application in the Precious Stone Mountain hydrothermal field

Hydrothermal plume is an important constituent of seabed hydrothermal circulation and is also one of the characteristics of active hydrothermal vents. Portable Miniature Autonomous Plume Recorders （MAPR） attached to a towed deep-sea instrument was used to search for hydrothermal plumes and hydrothermal vents. We introduced the basic principle of MAPR based on deep towing technology to detect plumes, then analyzed the factors affecting the quality of the MAPR data and presented a data correction method for MAPR, including instrument location correction, noise reduction processing, system error elimination and seawater background reduction. Finally we applied the method to analyze MAPR data obtained during the Chinese DY115-21 cruise on R/VDayang Iin the “Precious Stone Mountain” hydrothermal field on the Gala-pagos Microplate. The results provided a better understanding of the distribution of the hydrothermal activ-ity in this field, indicating the presence of a new hydrothermal vent.     

深海化能生态系统双壳纲共生体系互作机制研究进展

双壳纲贝类在深海特殊生境——热液、冷泉及有机沉落生态系统中分布广泛,并且在其体内常含有化能共生细菌为贝类提供营养物质.双壳纲贝类与化能共生菌形成的共生体系对于其适应深海还原性生境至关重要.近40a来随着海洋科考力度加大,深海化能生境的神秘面纱被逐渐揭开,越来越多的深海物种被发现,双壳纲贝类无疑是这些化能生态系统中的优势...     

Extensive deep-sea dispersal of postlarval shrimp from a hydrothermal vent

Hydrothermal vent fields on the Mid-Atlantic Ridge (MAR) are small (no more than 0.1-1.0 km²) and widely spaced (a reported average of one field per 175 km between 11°N and 40°N). Their faunas are similar and usually dominated by shrimp of the family Bresiliidae. Little is known about the way these animals (and other members of the vent fauna) disperse and colonize new vents. Vent shrimp juveniles have been taken close to certain vent sites, and in midwater, but their larvae and postlarvae have not been captured. We report here that bresiliid shrimp postlarvae are very widely dispersed around the Broken Spur vent field and extend into the next MAR segment and the Atlantis Fracture Zone beyond. The populations show density gradients declining both vertically and horizontally from the vent site, in contrast to the overall pelagic biomass. This is the furthest recorded dispersal (> 100 km) of identified larvae from a hydrothermal vent and is sufficient to give them access to adjacent vent fields and thus the scope for colonising new sites.     

The correlation between bioaccumulation and pattern of stress-related genes expression of black sea bream (<Emphasis Type="Italic">Acanthopagrus schlegeli</Emphasis>) by cadmium exposure

In order to correlate the expression of detoxifying enzyme genes and Cd accumulation in black sea bream, we analyzed four tissues (brain, gills, liver, and muscle) from black sea breams that were exposed to four different concentrations of Cd (0, 2, 13, and 25 mg/L) for various durations (0, 24, 48, 72, and 96 h). The highest level of Cd was accumulated in the liver, followed by the gills, brain, and muscle. The accumulation of Cd was significantly correlated with the duration of exposure and the concentration in brain, gill, and liver tissue, but not in muscle tissue, and the rate of accumulation increased with Cd concentration. The expression of metallothionein II (MT II) mRNA exhibited a similar pattern as Cd accumulation, especially in that the expression of MT II mRNA decreased in muscle tissue with increases in exposure duration. In contrast, the expression of cytochrome P450 1A (CYP1A) mRNA was highest in the liver, followed by brain, muscle, and gill tissues, and in gills and muscle tissue of Cd-exposed fish, the expression of CYP1A mRNA fell below that of the control fish. Overall, the liver of black sea bream was the most sensitive to Cd exposure, and the expression of MT II mRNA was 200-fold greater than the control fish. These findings indicate that the detoxification mechanisms of black sea bream are influenced by both MT II and CYP1A and that the genes participate in the detoxification of different tissues.     

Peripheral communities of the Eastern Lau Spreading Center and Valu Fa Ridge: community composition,temporal change and comparison to near‐vent communities

Western Pacific hydrothermal vents will soon be subjected to deep‐sea mining and peripheral sites are considered the most practical targets. The limited information on community dynamics and temporal change in these communities makes it difficult to anticipate the impact of mining activities and recovery trajectories. We studied community composition of peripheral communities along a cline in hydrothermal chemistry on the Eastern Lau Spreading Center and Valu Fa Ridge (ELSC‐VFR) and also studied patterns of temporal change. Peripheral communities located in the northern vent fields of the ELSC‐VFR are significantly different from those in the southern vent fields. Higher abundances of zoanthids and anemones were found in northern peripheral sites and the symbiont‐containing mussel Bathymodiolus brevior, brisingid seastars and polynoids were only present in the northern peripheral sites. By contrast, certain faunal groups were seen only in the southern peripheral sites, such as lollipop sponges, pycnogonids and ophiuroids. Taxonomic richness of the peripheral communities was similar to that of active vent communities, due to the presence of non‐vent endemic species that balanced the absence of species found in areas of active venting. The communities present at waning active sites resemble those of peripheral sites, indicating that peripheral species can colonize previously active vent sites in addition to settling in the periphery of areas of venting. Growth and mortality were observed in a number of the normally slow‐growing cladorhizid stick sponges, indicating that these animals may exhibit life history strategies in the vicinity of vents that differ from those previously recorded. A novel facultative association between polynoids and anemones is proposed based on their correlated distributions.