Vent Sites Research Articles

Isolation and Antibiotic Screening of Fungi from a Hydrothermal Vent Site and Characterization of Secondary Metabolites from a Penicillium Isolate.

Five new compounds were isolated from Penicillium sp. Y-5-2 including an austin derivative 4, four isocoumarins 9, 11, 12, and 13, together with two known isocoumarins 8 and 10, and six known austin derivatives 1, 2, 3, 5, 6, and 7 and one phenol 14. Their structures and relative configurations were established by spectroscopic means. The absolute configurations of 4, 11, and 13 were defined mainly by comparison of quantum chemical TDDFT calculated and experimental ECD spectra. The cyclization of the pentan-2-ol pendant at C-3 in compound 13 allowed the assignment of a new 2,3,4,4a,6,10b-hexahydro-1H-benzo[c]chromene isocoumarin skeleton. New compounds 9, 11, and 13 revealed inhibitory activities against E. coli at MIC values around 32μg/mL. The known compound 14 showed potent antibiotic activity against Staphylococcus aureus and Bacillus subtilis with MIC values 8 and 2μg/mL, respectively, with no cytotoxicity when tested in vitro. A rapid and efficient technique for selecting antibiotic fungal strain among eight marine-derived fungi was also described.

Larval Connectivity between Deep‐Sea Hydrothermal Vents via Surface Waters

All photographs in this section are provided by authors of papers in our scientific journals and are used by permission.All copyrights reserved. Larval dispersal significantly contributes to the population dynamics, biogeography, and evolutionary processes of invertebrate animals endemic to hydrothermal vents—patchily distributed, ephemeral habitats in the deep sea. Converging evidence from swimming behavior, temperature optimum, and population genetics strongly suggests that the planktotrophic larvae of the red-blooded limpet Shinkailepas myojinensis migrate vertically to the photic zone to take advantage of richer food supplies and stronger currents. Sea surface temperature may represent a critical factor in determining the geographic distribution of many vent-endemic species with a planktotrophic early development, and in turn the faunal composition of individual vent sites and regions. These photographs illustrate the article “Do larvae from deep-sea hydrothermal vents disperse in surface waters?” by Takuya Yahagi, Hiromi Kayama Watanabe, Shigeaki Kojima, and Yasunori Kano, published in Ecology. https://doi.org/10.1002/ecy.1800

In situ estimates of iron-oxidation and accretion rates for iron-oxidizing bacterial mats at Lō’ihi Seamount

It is increasingly recognized that diffuse, hydrothermal venting is an important source of iron to the deep-sea that can influence oceanic iron dynamics and abundance. Lithotrophic Fe-oxidizing bacteria (FeOB) are dominant at diffuse hydrothermal vent sites, producing microbial iron mats that are often centimeters or more thick. At present, little is known about in situ growth rates of FeOB, specific Fe-oxidation rates, or accretion rates for iron mats. An in situ productivity chamber was developed that took advantage of the unique mineral morphotypes produced by FeOB to estimate rates of Fe-oxidation and accretion. Chambers were placed at two diffuse vents (1179 and 1300mbsl) at Lō’ihi Seamount where they were colonized by FeOB for different amounts of time. From this analysis, it was estimated that Fe-oxidation rates could range from 8.2 to 51.9 × 10−6molh−1, and that iron mats could accrete at around 2.2cm. yr−1. Molecular analysis indicated that the relative abundance of Zetaproteobacteria, a group of known FeOB, accounted for 80–90% of the bacteria colonizing the chambers. There was a distinct difference between populations at the 1179m site (Pohaku), and the 1300m site (North Hiolo Ridge). Microscope slides placed within the productivity chambers were colonized by different morphotypes of FeOB. The cells responsible for one common morphotype that produces a Y-shaped filament were identified as Zetaproteobacteria by use of a small subunit rRNA probe. This work confirms the importance of FeOB in the formation of chemosynthetic iron mats, and provides the first estimates for in situ Fe-oxidation rates and mat accretion rates.

A Novel ω3-Desaturase in the Deep Sea Giant Tubeworm Riftia pachyptila

One paradox of the trophic biochemistry of the deep sea giant tubeworm Riftia pachyptila, endemic to hydrothermal vent sites and nourished by polyunsaturated fatty acid (PUFA) deficiency chemolitoautotrophic sulfide-oxidizing bacteria, is the source of their PUFAs. Biosynthesis of PUFA starts with two precursors C18:2n-6 and C18:3n-3, which cannot be biosynthesized by most animals due to lack of ω6- and ω3-desaturase; thus, C18:2n-6 and C18:3n-3 are generally essential fatty acids for animals. Here, we characterized a gene derived from the R. pachyptila located by hydrothermal vent, which encoded a novel ω3-desaturase (Rp3Fad). The gene was identified by searching the R. pachyptila transcriptome database using known ω3-desaturases, and its predicted protein showed 37-45% identical to ω3-desaturases of fungus and microalgae, and only 31% identitical to nematode Caenorhabditis elegans ω3-desaturase. Expression in yeast Saccharomyces cerevisiae showed that the Rp3Fad could desaturate C18:2n-6 and C18:3n-6 into C18:3n-3 and C18:4n-3, respectively, displaying a Δ15 activity similar to plant ω3-desaturase, but it showed no activity towards C20 n-6 PUFA substrates, differing from the well-characterized C. elegans ω3-desaturases. Δ5, Δ6, Δ8, and Δ12 activity were also tested, resulting in no corresponding production. The function of ω3-desaturase identified in R. pachyptila could produce C18:3n-3 used in synthesis of n-3 series PUFAs, suggesting an adaption to PUFA deficiency environment in deep sea hydrothermal vent.

Rates and processes affecting As speciation and mobility in lake sediments during aging

Sediments from an arsenic (As) contaminated groundwater vent site were used to investigate As(III) binding, transformation and redistribution in native and iron oxide amended lake sediments using aging spiked batch reactions and a sequential extraction procedure that maintains As(V) and As(III) speciation. In the native sediments, fractionation analysis revealed that 10% of the spiked As(III) remained intact after a 32-day aging experiment and was predominantly adsorbed to the strongly sorbed (NH4H2PO4 extractable) and amorphous Fe oxide bound (H3PO4 extractable) fractions. Kinetic modelling of the experimental results allowed identifying the dominant reaction path for depletion of dissolved As(III) to As(III) absorbed on to the solid phase, followed by oxidation in the solid phase. Arsenite was initially adsorbed primarily to the easily exchangeable fraction ((NH4)2SO4 extractable), then rapidly transformed into As(V) and redistributed to the strongly sorbed and amorphous Fe oxide bound fractions. Oxidation of As(III) in recalcitrant fractions was less efficient. The iron oxide amendments illustrated the controls that iron oxides can have on As(III) binding and transformation rates. In goethite amended samples As(III) oxidation was faster and primarily occurred in the strongly sorbed and amorphous Fe oxide bound fractions. In these samples, 19.3μg Mn was redistributed (compared to the native sediment) from the easily exchangeable and crystalline Fe oxide bound fractions to the strongly sorbed and amorphous Fe oxide bound fractions, indicating that goethite may act as a catalyst for Mn(II) oxidation, thereby producing sorbed Mn(III/IV), which then appears to be involved in rapidly oxidizing As(III).

Is the trophosome of Ridgeia piscesae monoclonal?

The hydrothermal vent tubeworm Ridgeia piscesae relies on intracellular chemolithoautotrophic symbionts for its nutrition. Yet, little is known about symbiont diversity within and between individual worms. We report several lines of molecular evidence for multiple genotypes of very closely related symbionts within the trophosome of the R. piscesae. We examined the distribution of genotypic variants (insertions, deletions, and substitutions) in whole genome shotgun sequences of symbionts from the trophosome of a unique individual R. piscesae and the pooled sequences of five other tubeworms of the same species. Observed heterogeneity is unlikely to be the result of recent point or structural mutations of a monoclonal symbiont lineage. To assess inter-host diversity we examined single nucleotide polymorphisms (SNPs) in pyrosequences of the highly variable regions V1 to V3 of the symbiont 16S rRNA gene across 53 individual hosts from two vent sites. Most of the identified SNPs were found in more than one individual, and one seemed to be region specific. Two of the identified SNPs were also present in metagenomic data generated from high-throughput sequencing of trophosome material from an individual R. piscesae. Finally, we observed compositional and structural variations of CRISPR spacers within a CRISPR array.

Do larvae from deep-sea hydrothermal vents disperse in surface waters?

Larval dispersal significantly contributes to the geographic distribution, population dynamics, and evolutionary processes of animals endemic to deep-sea hydrothermal vents. Little is known as to the extent that their larvae migrate vertically to shallower waters and experience stronger currents and richer food supplies. Here, we first provide evidence from early life-history traits and population genetics for the surface dispersal of a vent species. Planktotrophic larvae of a red blood limpet, Shinkailepas myojinensis (Gastropoda: Neritimorpha: Phenacolepadidae), were cultured to observe their swimming behavior and to evaluate the effects of temperature on survival and growth. In addition, the population structure was analyzed based on 1.2-kbp mitochondrial DNA sequences from 77 specimens that cover the geographic and bathymetric distributions of the species (northwest Pacific, 442-1,227m in depth). Hatched larvae constantly swam upward at 16.6-44.2mm/min depending on temperature. Vertical migration from hydrothermal vents to the surface, calculated to take ~4-43d, is attainable given their lengthy survival time without feeding. Fed larvae best survived and grew at 25°C (followed by 20°C), which approximates the sea surface temperature in the geographic range of the species. Little or no growth was observed at the temperature of the vent habitat where adult limpets occur (≤15°C). Population genetic analyses showed no differentiation among localities that are <1,350km apart. The larvae of S.myojinensis most likely migrate to the surface water, where high phytoplankton biomass and strong currents enable their growth and long distance dispersal over many months. Sea surface temperature may represent a critical factor in determining the geographic distribution of many vent endemic species with a planktotrophic early development, and in turn the faunal composition of individual vent sites and regions.

Altered epiphyte community and sea urchin diet in Posidonia oceanica meadows in the vicinity of volcanic CO2 vents

Ocean acidification (OA) predicted for 2100 is expected to shift seagrass epiphyte communities towards the dominance of more tolerant non-calcifying taxa. However, little is known about the indirect effects of such changes on food provision to key seagrass consumers. We found that epiphyte communities of the seagrass Posidonia oceanica in two naturally acidified sites (i.e. north and south sides of a volcanic CO2 vent) and in a control site away from the vent at the Ischia Island (NW Mediterranean Sea) significantly differed in composition and abundance. Such differences involved a higher abundance of non-calcareous crustose brown algae and a decline of calcifying polychaetes in both acidified sites. A lower epiphytic abundance of crustose coralline algae occurred only in the south side of the vents, thus suggesting that OA may alter epiphyte assemblages in different ways due to interaction with local factors such as differential fish herbivory or hydrodynamics. The OA effects on food items (seagrass, epiphytes, and algae) indirectly propagated into food provision to the sea urchin Paracentrotus lividus, as reflected by a reduced P. oceanica exploitation (i.e. less seagrass and calcareous epiphytes in the diet) in favour of non-calcareous green algae in both vent sites. In contrast, we detected no difference close and outside the vents neither in the composition of sea urchin diet nor in the total abundance of calcareous versus non-calcareous taxa. More research, under realistic scenarios of predicted pH reduction (i.e. ≤ 0.32 units of pH by 2100), is still necessary to better understand cascading effects of this altered urchin exploitation of food resources under acidified conditions on ecosystem diversity and function.

Niche partitioning of diverse sulfur-oxidizing bacteria at hydrothermal vents.

At deep-sea hydrothermal vents, primary production is carried out by chemolithoautotrophic microorganisms, with the oxidation of reduced sulfur compounds being a major driver for microbial carbon fixation. Dense and highly diverse assemblies of sulfur-oxidizing bacteria (SOB) are observed, yet the principles of niche differentiation between the different SOB across geochemical gradients remain poorly understood. In this study niche differentiation of the key SOB was addressed by extensive sampling of active sulfidic vents at six different hydrothermal venting sites in the Manus Basin, off Papua New Guinea. We subjected 33 diffuse fluid and water column samples and 23 samples from surfaces of chimneys, rocks and fauna to a combined analysis of 16S rRNA gene sequences, metagenomes and real-time in situ measured geochemical parameters. We found Sulfurovum Epsilonproteobacteria mainly attached to surfaces exposed to diffuse venting, while the SUP05-clade dominated the bacterioplankton in highly diluted mixtures of vent fluids and seawater. We propose that the high diversity within Sulfurimonas- and Sulfurovum-related Epsilonproteobacteria observed in this study derives from the high variation of environmental parameters such as oxygen and sulfide concentrations across small spatial and temporal scales.

Highlighting of quorum sensing lux genes and their expression in the hydrothermal vent shrimp Rimicaris exoculata ectosymbiontic community. Possible use as biogeographic markers.

Rimicaris exoculata is a caridean shrimp that dominates the fauna at several hydrothermal vent sites of the Mid-Atlantic Ridge. It has two distinct and stable microbial communities. One of these epibiontic bacterial communities is located in the shrimp gut and has a distribution and role that are poorly understood. The second colonizes its enlarged gill chamber and is involved in host nutrition. It is eliminated after each molt, and has colonization processes reminiscent of those of a biofilm. The presence and expression of genes usually involved in quorum sensing (QS) were then studied. At four sites, Rainbow, TAG, Snake Pit and Logatchev, two lux genes were identified in the R. exoculata epibiontic community at different shrimp molt stages and life stages. RT-PCR experiments highlighted lux gene expression activity at TAG, Snake Pit and Rainbow vent sites. Their potential QS activity and their possible roles in epibiont colonization processes are discussed. Moreover, phylogenetic analysis has shown the presence of three clades for luxS (Epsilonproteobacteria) and four clades for luxR (Gammaproteobacteria) genes, each clade being restricted to a single site. These genes are more divergent than the 16S rRNA one. They could therefore be used as biogeographical genetic markers.

Boiling vapour-type fluids from the Nifonea vent field (New Hebrides Back-Arc, Vanuatu, SW Pacific): Geochemistry of an early-stage, post-eruptive hydrothermal system

In 2013, high-temperature vent fluids were sampled in the Nifonea vent field. This field is located within the caldera of a large shield-type volcano of the Vate Trough, a young extensional rift in the New Hebrides back-arc. Hydrothermal venting occurs as clear and black smoker fluids with temperatures up to 368°C, the hottest temperatures measured so far in the western Pacific.The physico-chemical conditions place the fluids within the two-phase field of NaCl–H2O, and venting is dominated by vapour phase fluids with Cl concentrations as low as 25mM. The fluid composition, which differs between the individual vent sites, is interpreted to reflect the specific geochemical fluid signature of a hydrothermal system in its initial, post-eruptive stage. The strong Cl depletion is accompanied by low alkali/Cl ratios compared to more evolved hydrothermal systems, and very high Fe/Cl ratios. The concentrations of REY (180nM) and As (21μM) in the most Cl-depleted fluid are among the highest reported so far for submarine hydrothermal fluids, whereas the inter-element REY fractionation is only minor.The fluid signature, which has been described here for the first time in a back-arc setting, is controlled by fast fluid passage through basaltic volcanic rocks, with extremely high water-rock ratios and only limited water-rock exchange, phase separation and segregation, and (at least) two-component fluid mixing. Metals and metalloids are unexpectedly mobile in the vapour phase fluids, and the strong enrichments of Fe, REY, and As highlight the metal transport capacity of low-salinity, low-density vapours at the specific physico-chemical conditions at Nifonea. One possible scenario is that the fluids boiled before the separated vapour phase continued to react with fresh glassy lavas. The mobilization of metals is likely to occur by leaching from fresh glass and grain boundaries and is supported by the high water/rock ratios. The enrichment of B and As is further controlled by their high volatility, whereas the strong enrichment of REY is also a consequence of the elevated concentrations in the host rocks. However, a direct contribution of metals such as As from magmatic degassing cannot be ruled out. The different fluid end-member composition of individual vent sites could be explained by mixing of vapour phase fluids with another fluid phase of different water/rock interaction history.

Fungi associated with chimney and sulfide samples from a South Mid-Atlantic Ridge hydrothermal site: Distribution, diversity and abundance

Deep-sea hydrothermal vent ecosystems are known to support remarkably diverse microbial communities, ranging from chemoautotrophic prokaryotes to heterotrophic prokaryotes and microeukaryotes. While fungi have generally been identified as an important component of various microbial communities in the environment, little is known about the species richness and abundance of such microorganisms in deep-sea hydrothermal vent ecosystems. In this study, a combined culture-dependent and culture-independent sequence-based approach was used to investigate fungal distribution and diversity at a deep-sea hydrothermal vent site located at the Mid-Atlantic Ridge of the South Atlantic Ocean. Sequence analyses showed that the fungal community was dominated by members of the Ascomycota and the Basidiomycota. Several new phylotypes (28 of 65 total fungal OTUs and 2 of 19 culturable fungal phylotypes) were identified, contributing to the literally unknown diversity of fungi in this understudied habitat. The fungal community structures in the chimney samples were distinct from those in three sulfide samples. The qPCR results revealed that fungal LSU rRNA gene copy numbers ranged from 5.88×105 to 6.77×106 copies/gram rock (wet weight), and the Ascomycota was significantly more abundant 2–3 orders) than the Basidiomycota. Our findings provide new insights into the diversity and abundance of fungi in deep-sea hydrothermal vent ecosystems, which increases our knowledge and understanding of the fungal diversity in deep-sea environments.

Mineralogy, geochemistry, and Sr-Pb isotopic geochemistry of hydrothermal massive sulfides from the 15.2°S hydrothermal field, Mid-Atlantic Ridge

Abstract The 15.2°S hydrothermal field is located at 15.2°S, 13.4°W within the Mid-Atlantic Ridge (MAR) and was initially discovered during Cruise DY125-22 by the Chinese expedition during R/V Dayangyihao in 2011. Here, we provide detailed mineralogical, bulk geochemical, and Sr–Pb isotopic data for massive sulfides and basalts from the 15.2°S hydrothermal field to improve our understanding of the mineral compositions, geochemical characteristics, type of hydrothermal field, and the source of metals present at this vent site. The samples include 14 massive sulfides and a single basalt. The massive sulfides are dominated by pyrite with minor amounts of sphalerite and chalcopyrite, although a few samples also contain minor amounts of gordaite, a sulfate mineral. The sulfides have bulk compositions that contain low concentrations of Cu + Zn (mean 7.84 wt%), Co (mean 183 ppm), Ni (mean 3 ppm), and Ba (mean 16 ppm), similar to the Normal Mid-Ocean Ridge Basalt (N-MORB) type deposits along the MAR but different to the compositions of the Enriched-MORB (E-MORB) and ultramafic type deposits along this spreading ridge. Sulfides from the study area have Pb isotopic compositions (206Pb/204Pb = 18.4502–18.4538, 207Pb/204Pb = 15.4903–15.4936, 208Pb/204Pb = 37.8936–37.9176) that are similar to those of the basalt sample (206Pb/204Pb = 18.3381, 207Pb/204Pb = 15.5041, 208Pb/204Pb = 37.9411), indicating that the metals within the sulfides were derived from leaching of the surrounding basaltic rocks. The sulfides also have 87Sr/86Sr ratios (0.708200–0.709049) that are much higher than typical MAR hydrothermal fluids (0.7028–0.7046), suggesting that the hydrothermal fluids mixed with a significant amount of seawater during massive sulfide precipitation.

Variations in pockmark composition at the Vestnesa Ridge: Insights from marine controlled source electromagnetic and seismic data

AbstractThe Vestnesa Ridge marks the northern boundary of a known submarine gas hydrate province in the west Svalbard margin. Several seafloor pockmarks at the eastern segment of the ridge are sites of active methane venting. Until recently, seismic reflection data were the main tool for imaging beneath the ridge. Coincident controlled source electromagnetic (CSEM), high‐resolution two‐dimensional (2‐D) airgun, sweep frequency SYSIF, and three‐dimensional (3‐D) p‐cable seismic reflection data were acquired at the south‐eastern part of the ridge between 2011 and 2013. The CSEM and seismic data contain profiles across and along the ridge, passing several active and inactive pockmarks. Joint interpretation of resistivity models obtained from CSEM and seismic reflection data provides new information regarding the fluid composition beneath the pockmarks. There is considerable variation in transverse resistance and seismic reflection characteristics of the gas hydrate stability zone (GHSZ) between the ridge flanks and chimneys beneath pockmarks. Layered seismic reflectors on the flanks are associated with around 300 Ωm2 transverse resistance, whereas the seismic reflectors within the chimneys exhibit amplitude blanking and chaotic patterns. The transverse resistance of the GHSZ within the chimneys vary between 400 and 1200 Ωm2. Variance attributes obtained from the 3‐D p‐cable data also highlight faults and chimneys, which coincide with the resistivity anomalies. Based on the joint data interpretation, widespread gas hydrate presence is likely at the ridge, with both hydrates and free gas contained within the faults and chimneys. However, at the active chimneys the effect of gas likely dominates the resistive anomalies.

Bacterial activity in hydrogenetic ferromanganese crust from the Indian Ocean: a combined geochemical, experimental and pyrosequencing study

The Afanasiy-Nikitin Seamount (ANS) in the Equatorial Indian Ocean harbors hydrogenetic ferromanganese (Fe–Mn) crusts. It was hypothesized that the bacteria associated with the crust catalyze the precipitation of metal hydroxides in seawater more than abiotic dissolution, contributing to hydrogenetic accretion on the seamount. To test this hypothesis, Fe–Mn crust samples were collected from the flanks of the ANS. Geochemical properties of water samples collected were analyzed, and simulatory laboratory experiments were conducted to quantify bacterial accretion rates. Pyrosequencing was used to delineate the community associated with the crust. The environmental parameters of the water column indicated significant differences (p Mn (0.63) > Ni (0.003) > Co (0.002 mg g−1) with added glucose (0.01%) and Fe (9.09) > Mn (0.87) > Ni (0.0043) > Co (0.0008 mg g−1) without added glucose. Unlike the hydrothermal vent sites of the Pacific where e- and ζ-Proteobacteria were reported to be dominant, the hydrogenetic Fe–Mn crusts of the ANS revealed sequences related to known Fe-, Mn- and S-oxidizing bacteria of the γ- and α-Proteobacterial groups. Thus, the different selective pressures in the two environments could be one of the factors that have brought about a difference in their bacterial diversity. Besides, the ambient nutrient levels could have triggered the participation of the Proteobacterial community of the ANS in the precipitation of Fe–Mn rich minerals.

Metabolic Profiling as a Screening Tool for Cytotoxic Compounds: Identification of 3-Alkyl Pyridine Alkaloids from Sponges Collected at a Shallow Water Hydrothermal Vent Site North of Iceland.

Twenty-eight sponge specimens were collected at a shallow water hydrothermal vent site north of Iceland. Extracts were prepared and tested in vitro for cytotoxic activity, and eight of them were shown to be cytotoxic. A mass spectrometry (MS)-based metabolomics approach was used to determine the chemical composition of the extracts. This analysis highlighted clear differences in the metabolomes of three sponge specimens, and all of them were identified as Haliclona (Rhizoniera) rosea (Bowerbank, 1866). Therefore, these specimens were selected for further investigation. Haliclona rosea metabolomes contained a class of potential key compounds, the 3-alkyl pyridine alkaloids (3-APA) responsible for the cytotoxic activity of the fractions. Several 3-APA compounds were tentatively identified including haliclamines, cyclostellettamines, viscosalines and viscosamines. Among these compounds, cyclostellettamine P was tentatively identified for the first time by using ion mobility MS in time-aligned parallel (TAP) fragmentation mode. In this work, we show the potential of applying metabolomics strategies and in particular the utility of coupling ion mobility with MS for the molecular characterization of sponge specimens.

Linking gene expression to productivity to unravel long- and short-term responses of seagrasses exposed to CO2 in volcanic vents

Ocean acidification is a major threat for marine life but seagrasses are expected to benefit from high CO2. In situ (long-term) and transplanted (short-term) plant incubations of the seagrass Cymodocea nodosa were performed near and away the influence of volcanic CO2 vents at Vulcano Island to test the hypothesis of beneficial effects of CO2 on plant productivity. We relate, for the first time, the expression of photosynthetic, antioxidant and metal detoxification-related genes to net plant productivity (NPP). Results revealed a consistent pattern between gene expression and productivity indicating water origin as the main source of variability. However, the hypothesised beneficial effect of high CO2 around vents was not supported. We observed a consistent long- and short-term pattern of gene down-regulation and 2.5-fold NPP decrease in plants incubated in water from the vents and a generalized up-regulation and NPP increase in plants from the vent site incubated with water from the Reference site. Contrastingly, NPP of specimens experimentally exposed to a CO2 range significantly correlated with CO2 availability. The down-regulation of metal-related genes in C. nodosa leaves exposed to water from the venting site suggests that other factors than heavy metals, may be at play at Vulcano confounding the CO2 effects.

Phytoplankton primary productivity around submarine groundwater discharge in nearshore coasts

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 563:25-33 (2017) - DOI: https://doi.org/10.3354/meps11980 Phytoplankton primary productivity around submarine groundwater discharge in nearshore coasts Ryo Sugimoto1,*, Katsuhiro Kitagawa1, Saori Nishi1, Hisami Honda1,2, Makoto Yamada2, Shiho Kobayashi3, Jun Shoji4, Shinji Ohsawa5, Makoto Taniguchi2, Osamu Tominaga1 1Faculty of Marine Biosciences, Fukui Prefectural University, Obama, Fukui 917-0003, Japan 2Research Institute for Humanity and Nature, Kyoto 603-8047, Japan 3Field Science Education and Research Center, Kyoto University, Kyoto 606-0068, Japan 4Graduate School of Biosphere Science, Hiroshima University, Hiroshima 739-8528, Japan 5Institute for Geothermal Sciences, Kyoto University, Oita 874-0903, Japan *Corresponding author: sugiryo@fpu.ac.jp ABSTRACT: Nutrients supplied from submarine groundwater discharge (SGD) are generally thought to enhance primary production in coastal seas. However, there is little evidence for a direct association between SGD and phytoplankton primary productivity. To elucidate the response of in situ primary productivity to SGD, we conducted comparative experiments at 3 coastal sites in Japan with different SGD types (Site A: Obama Bay; Site B: coast along the western foot of Mt. Chokai; Site C: Beppu Bay) during the summers of 2013-2015. At Site A, which is characterized by seepage-type SGD, we found a significant positive relationship between in situ primary productivity and 222Rn concentration. This was likely driven by nutrient-limited water column conditions. On the other hand, at the volcanic coastal Sites B and C, which are dominated by spring-type SGD, no clear relationships between in situ primary productivity and 222Rn concentration were found. Although significant relationships between nutrient concentrations and 222Rn concentration suggest that SGD acts as a primary nutrient source in these regions, the non-trivial influence of light availability complicates those relationships. Furthermore, lower biomass-specific primary productivity around submarine springs at both sites suggests that submarine springs have negative impacts on phytoplankton growth rates around vent sites, possibly due to changes in local environmental conditions. Our study clarified that the mechanism by which SGD affects phytoplankton production differs from one ecosystem to another because of variable hydrogeographical properties, such as the type of groundwater discharge (i.e. spring or seepage). KEY WORDS: In situ primary productivity · Submarine groundwater discharge · 222Rn Full text in pdf format PreviousNextCite this article as: Sugimoto R, Kitagawa K, Nishi S, Honda H and others (2017) Phytoplankton primary productivity around submarine groundwater discharge in nearshore coasts. Mar Ecol Prog Ser 563:25-33. https://doi.org/10.3354/meps11980 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 563. Online publication date: January 20, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Opposing authigenic controls on the isotopic signature of dissolved iron in hydrothermal plumes

Iron is a scarce but essential micronutrient in the oceans that limits primary productivity in many regions of the surface ocean. The mechanisms and rates of Fe supply to the ocean interior are still poorly understood and quantified. Iron isotope ratios of different Fe pools can potentially be used to trace sources and sinks of the global Fe biogeochemical cycle if these boundary fluxes have distinct signatures. Seafloor hydrothermal vents emit metal rich fluids from mid-ocean ridges into the deep ocean. Iron isotope ratios have the potential to be used to trace the input of hydrothermal dissolved iron to the oceans if the local controls on the fractionation of Fe isotopes during plume dispersal in the deep ocean are understood. In this study we assess the behaviour of Fe isotopes in a Southern Ocean hydrothermal plume using a sampling program of Total Dissolvable Fe (TDFe), and dissolved Fe (dFe). We demonstrate that δ56Fe values of dFe (δ56dFe) within the hydrothermal plume change dramatically during early plume dispersal, ranging from −2.39±0.05‰ to −0.13±0.06‰ (2 SD). The isotopic composition of TDFe (δ56TDFe) was consistently heavier than dFe values, ranging from −0.31±0.03‰ to 0.78±0.05‰, consistent with Fe oxyhydroxide precipitation as the plume samples age. The dFe present in the hydrothermal plume includes stabilised dFe species with potential to be transported to the deep ocean. We estimate that stable dFe exported from the plume will have a δ56Fe of −0.28±0.17‰. Further, we show that the proportion of authigenic iron-sulfide and iron-oxyhydroxide minerals precipitating in the buoyant plume exert opposing controls on the resultant isotope composition of dissolved Fe passed into the neutrally buoyant plume. We show that such controls yield variable dissolved Fe isotope signatures under the authigenic conditions reported from modern vent sites elsewhere, and so ought to be considered during iron isotope reconstructions of past hydrothermalism from ocean sediment records.

In situ developmental responses of tropical sea urchin larvae to ocean acidification conditions at naturally elevated pCO2 vent sites.

Laboratory experiments suggest that calcifying developmental stages of marine invertebrates may be the most ocean acidification (OA)-sensitive life-history stage and represent a life-history bottleneck. To better extrapolate laboratory findings to future OA conditions, developmental responses in sea urchin embryos/larvae were compared under ecologically relevant in situ exposures on vent-elevated pCO2 and ambient pCO2 coral reefs in Papua New Guinea. Echinometra embryos/larvae were reared in meshed chambers moored in arrays on either venting reefs or adjacent non-vent reefs. After 24 and 48 h, larval development and morphology were quantified. Compared with controls (mean pH(T) = 7.89-7.92), larvae developing in elevated pCO2 vent conditions (pH(T) = 7.50-7.72) displayed a significant reduction in size and increased abnormality, with a significant correlation of seawater pH with both larval size and larval asymmetry across all experiments. Reciprocal transplants (embryos from vent adults transplanted to control conditions, and vice versa) were also undertaken to identify if adult acclimatization can translate resilience to offspring (i.e. transgenerational processes). Embryos originating from vent adults were, however, no more tolerant to reduced pH. Sea temperature and chlorophyll-a concentrations (i.e. larval nutrition) did not contribute to difference in larval size, but abnormality was correlated with chlorophyll levels. This study is the first to examine the response of marine larvae to OA scenarios in the natural environment where, importantly, we found that stunted and abnormal development observed in situ are consistent with laboratory observations reported in sea urchins, in both the direction and magnitude of the response.