Posts Tagged 'vents'

Elevated trace elements in sediments and seagrasses at CO2 seeps

Highlights
• Sandy CO2 seep sediments had higher concentration of trace elements.

• Metals can be more toxic in areas affected by CO2 acidification, with adverse effects on the sediment associated biota.

• Seagrasses element accumulation at CO2 seeps was highest in the roots.

Abstract
Seagrasses often occur around shallow marine CO2 seeps, allowing assessment of trace metal accumulation. Here, we measured Cd, Cu, Hg, Ni, Pb and Zn levels at six CO2 seeps and six reference sites in the Mediterranean. Some seep sediments had elevated metal concentrations; an extreme example was Cd which was 43x more concentrated at a seep than its reference. Three seeps had metal levels that were predicted to adversely affect marine biota, namely Vulcano (for Hg), Ischia (for Cu) and Paleochori (for Cd and Ni). There were higher-than-sediment levels of Zn and Ni in Posidonia oceanica and of Zn in Cymodocea nodosa, particularly in roots. High levels of Cu were found in Ischia seep sediments, yet seagrass was abundant, and the plants contained low levels of Cu. Differences in bioavailability and toxicity of trace elements helps explain why seagrasses can be abundant at some CO2 seeps but not others.

Continue reading ‘Elevated trace elements in sediments and seagrasses at CO2 seeps’

Marine microbial community dynamics and responses to ocean acidification

Marine microbes, including both eukaryotes and prokaryotes, are the basal components of marine food webs and play a fundamental role in global biogeochemical cycling. Marine phytoplankton are responsible for approximately 50% of Earth’s primary production, while heterotrophic bacteria and archaea modulate carbon and nutrient cycling in the marine environment. The structure and function of marine microbial communities are closely coupled. Consequently, understanding the factors which govern the distribution of marine microbes through space and time has key implications for food webs and biogeochemical cycling. The development of high-throughput sequencing technologies has revolutionised marine microbial ecology by facilitating the profiling of microbial communities in high taxonomic resolution. In this thesis high-throughput sequencing of the 16S and 18S rRNA genes was used to achieve two major aims. The first aim was to investigate the ecological processes which underpin microbial community assembly in the marine environment. The second aim was to investigate the responses of marine microbial communities to near- future ocean acidification.

Two studies were performed towards the first aim of this thesis. In the first study, the microbial biogeography of the South Pacific Gyre was characterised across three depths at 22 stations along a 2,000 km longitudinal transect of the region. Microbial community composition was homogenous across horizontal spatial scales in the surface waters of the South Pacific Gyre, but varied significantly between surface waters and the deep chlorophyll maximum. A null model approach was used to unveil the ecological processes driving microbial community assembly in the region. Microbial communities in the surface waters were assembled primarily through the deterministic process of homogeneous selection, indicating that selection pressures were sufficient to overwhelm the influence of dispersal effects and ecological drift across vast horizontal spatial distances in the region. Dispersal limitation was comparatively more influential in the assembly of microbial communities between the surface waters and the deep chlorophyll maximum, indicating that stochastic processes play a significant role in microbial community assembly between these contiguous water masses.

In the second study, the bacterioplankton and protist biogeography of the Southland Front system was characterised in surface waters at 24 stations spanning four water masses. Both bacterioplankton and protist communities displayed significant structuring according to water mass, although this effect was most pronounced in bacterioplankton communities. A null model approach revealed that bacterioplankton communities were primarily assembled through homogeneous selection, while protist communities were primarily assembled through dispersal limitation and ecological drift across the Southland Front system. These findings highlight that distinct ecological processes can underpin the assembly of co- occurring bacterioplankton and protist communities, and that hydrographic features such as oceanic fronts play an important role in structuring both bacterioplankton and protist communities.

Two studies were conducted towards the second aim of this thesis. In the first study, the effect of ocean acidification and warming on bacterioplankton communities was investigated at the fringe and ultra-oligotrophic centre of the South Pacific Gyre using trace-metal clean deckboard incubation experiments. Bacterioplankton community composition and function were resistant to ocean acidification alone, and combined with warming, at the fringe of the South Pacific Gyre. Subtle but significant responses of bacterioplankton community composition to ocean acidification were observed at the ultra- oligotrophic centre of the South Pacific Gyre. These results suggest that bacterioplankton community responses to ocean acidification may be modulated by nutrient regimes. Nonetheless, the findings of this study did not diverge substantially from the narrative that bacterioplankton communities are resistant to near-future acidification.

In the second study, the effect of ocean acidification on both prokaryotic and eukaryotic biofilm communities was investigated at the Shikine-Jima CO2 seep system in Japan. The composition of both prokaryotic and eukaryotic communities was profoundly affected by ocean acidification through early successional stages, though these responses were not associated with shifts in community diversity or evenness. Notably, the relative abundance of the nuisance algae Prymnesium sp. and Biddulphia biddulphiana were enhanced under high CO2 conditions. These findings suggest that benthic biofilm communities may be vulnerable to near-future ocean acidification, and that changes in biofilm community composition may contribute to the reorganisation of coastal ecosystem observed at CO2 seeps globally.

In its entirety, this thesis significantly contributes to our understanding of the spatial dynamics of marine microbial communities by revealing the highly deterministic nature of bacterioplankton community assembly in the coastal waters and central gyre of the South Pacific Ocean. Furthermore, the findings of this thesis highlight the dominance of stochastic processes in structuring marine protist communities across short spatial scales, which may contribute to challenges in correlating abiotic environmental variables with marine protist community composition through space. The resistance of bacterioplankton communities to ocean acidification at the fringe of the South Pacific Gyre, and subtle responses to ocean acidification at the ultra-oligotrophic centre of the South Pacific Gyre broadly support the notion that bacterioplankton communities are resilient to near-future ocean acidification. In contrast, the composition of both prokaryotic and eukaryotic biofilm communities was profoundly affected by ocean acidification, leading to the proliferation of harmful algae with potentially severe consequences for coastal marine environments.

Continue reading ‘Marine microbial community dynamics and responses to ocean acidification’

Changes in the metabolic potential of the sponge microbiome under ocean acidification

Anthropogenic CO2 emissions are causing ocean acidification, which can affect the physiology of marine organisms. Here we assess the possible effects of ocean acidification on the metabolic potential of sponge symbionts, inferred by metagenomic analyses of the microbiomes of two sponge species sampled at a shallow volcanic CO2 seep and a nearby control reef. When comparing microbial functions between the seep and control sites, the microbiome of the sponge Stylissa flabelliformis (which is more abundant at the control site) exhibits at the seep reduced potential for uptake of exogenous carbohydrates and amino acids, and for degradation of host-derived creatine, creatinine and taurine. The microbiome of Coelocarteria singaporensis (which is more abundant at the seep) exhibits reduced potential for carbohydrate import at the seep, but greater capacity for archaeal carbon fixation via the 3-hydroxypropionate/4-hydroxybutyrate pathway, as well as archaeal and bacterial urea production and ammonia assimilation from arginine and creatine catabolism. Together these metabolic features might contribute to enhanced tolerance of the sponge symbionts, and possibly their host, to ocean acidification.

Continue reading ‘Changes in the metabolic potential of the sponge microbiome under ocean acidification’

Effects of long-term exposure to reduced pH conditions on the shell and survival of an intertidal gastropod

Highlights

• Prolonged exposures to high pCO2 can severely affect Phorcus sauciatus shell.

• No effects of high pCO2 were found on size-frequency or population density of P. sauciatus.

• Shells from reduced pH sites exhibited a higher shell aspect ratio and greater percentages of shell dissolution and break.

• Shells from high pCO2 areas exhibited changes in mechanical strength.

• Similar desiccation tolerance was found among contrasting environment populations.

Abstract

Volcanic CO2 vents are useful environments for investigating the biological responses of marine organisms to changing ocean conditions (Ocean acidification, OA). Marine shelled molluscs are highly sensitive to changes in seawater carbonate chemistry. In this study, we investigated the effects of reduced pH on the intertidal gastropod, Phorcus sauciatus, in a volcanic CO2 vent off La Palma Island (Canary Islands, North East Atlantic Ocean), a location with a natural pH gradient ranging from 7.0 to 8.2 over the tidal cycles. Density and size-frequency distribution, shell morphology, shell integrity, fracture resistance, and desiccation tolerance were evaluated between populations from control and CO2 vent sites. We found no effects of reduced pH on population parameters or desiccation tolerance across the pH gradient, but significant differences in shell morphology, shell integrity, and fracture resistance were detected. Individuals from the CO2 vent site exhibited a higher shell aspect ratio, greater percentages of shell dissolution and break, and compromised shell strength than those from the control site. Our results highlight that long-term exposure to high pCO2 can negatively affect the shell features of P. sauciatus but may not have a significant effect on population performance. Moreover, we suggest that loss of shell properties could lead to changes in predator-prey interactions.

Continue reading ‘Effects of long-term exposure to reduced pH conditions on the shell and survival of an intertidal gastropod’

Geochemical characterization of highly diverse hydrothermal fluids from volcanic vent systems of the Kermadec intraoceanic arc

During the R/V Sonne cruise SO253 in 2016/2017, hydrothermal vent sites along the Kermadec intraoceanic arc were sampled for hydrothermal fluids at four active volcanoes: Macauley, Haungaroa, Brothers and Rumble III, respectively. Water depths ranged between 290 m and 1700 m. A new vent field was discovered at Haungaroa. The samples were taken from diffuse-flow sites as well as from white and black smokers – rich in metals and gases – with discharge temperatures as high as 311 °C. Their fluid composition is very variable but basically divides into two types: one that indicates distinct magmatic input and another that shows evidence for intense water-rock interaction under hot, acidic conditions.

Fluid samples from Macauley, the shallowest sampling site (~300 m), had Fe concentrations as high as 1.7 mM, Al concentrations up to 122 μM and H2S up to 10 mM at a pH of only 1.2. At Brothers, the deepest sampling site (down to 1600 m), we identified two different fluid types: 1) A magmatically-influenced type at the Upper and Lower Cone with highest temperatures of 115 °C, up to 95.6 mM Mg (the highest Mg concentration measured in fluids from intraoceanic arc systems so far), elevated SO42− (76.9 mM), high H2S (5.0 mM), but Fe concentrations of only 15 μM and 2) A fluid with low Mg (5.4 mM), low H2S (1.1 mM), temperatures reaching 311 °C and high Fe contents (12.4 mM) at the Upper Caldera and NW Caldera Wall, typical of a black smoker fluid. Chloride concentrations in all fluids were similar, or highly enriched when compared to seawater (e.g. up to 787 mM, brine fluids), with also one low-chlorinity vapor-phase fluid sample recovered, indicating that phase separation is occurring at Brothers. Unusual highly elevated Mg concentrations in fluids from the Brothers Lower Cone (95.6 mM, compared to 53.2 mM in ambient seawater) combined with highly elevated concentrations of SO42− (76.9 mM, compared to 29.0 mM in ambient seawater) indicate dissolution of Mg- and SO42−-bearing minerals in the subsurface, such as caminite.

Our data show how highly diverse and variable island arc systems can be with respect to their fluid chemistry, both spatially and temporally. It adds to the still limited data set of arc systems compared to mid-ocean ridges and supplies an important contribution towards a better understanding of geochemical processes along arc volcanoes.

The higher range in fluid chemistry together with shallower water depth implies that the fluids from intraoceanic arcs may contribute a significant fraction of dissolved metals not only to the global oceanic biogeochemical cycle but also into the photic zone, the area of highest bioproductivity.

Continue reading ‘Geochemical characterization of highly diverse hydrothermal fluids from volcanic vent systems of the Kermadec intraoceanic arc’

Ocean acidification impact on ascidian Ciona robusta spermatozoa: new evidence for stress resilience

Highlights

• Impact of ocean acidification on sperm quality of the ascidian Ciona robusta was investigated.

• Two experimental approaches were set up to simulate the ocean conditions predicted for the end of this century.

• Alteration of sperm motility, morphology and physiology was detected in short-term exposure.

• A rapid recovery of physiological conditions was observed within one week.

• New evidence of resilience in ascidian C. robusta spermatozoa in response to ocean acidification.

Abstract

Rising atmospheric CO2 is causing a progressive decrease of seawater pH, termed ocean acidification. Predicting its impact on marine invertebrate reproduction is essential to anticipate the consequences of future climate change on species fitness and survival. Ocean acidification may affect reproductive success either in terms of gamete or progeny quality threating species survival. Despite an increasing number of studies focusing on the effects of ocean acidification on the early life history of marine organisms, very few have investigated the effects on invertebrate gamete quality. In this study, we set up two experimental approaches simulating the ocean conditions predicted for the end of this century, in situ transplant experiments at a naturally acidified volcanic vent area along the Ischia island coast and microcosm experiments, to evaluate the short-term effects of the predicted near-future levels of ocean acidification on sperm quality of the ascidian Ciona robusta after parental exposure. In the first days of exposure to acidified conditions, we detected alteration of sperm motility, morphology and physiology, followed by a rapid recovery of physiological conditions that provide a new evidence of resilience of ascidian spermatozoa in response to ocean acidification. Overall, the short-term tolerance to adverse conditions opens a new scenario on the marine species capacity to continue to reproduce and persist in changing oceans.

Continue reading ‘Ocean acidification impact on ascidian Ciona robusta spermatozoa: new evidence for stress resilience’

Simulating and quantifying multiple natural subsea CO2 seeps at Panarea Island (Aeolian Islands, Italy) as a proxy for potential leakage from subseabed carbon storage sites

Carbon dioxide (CO2) capture and storage (CCS) has been discussed as a potentially significant mitigation option for the ongoing climate warming. Natural CO2 release sites serve as natural laboratories to study subsea CO2 leakage in order to identify suitable analytical methods and numerical models to develop best-practice procedures for the monitoring of subseabed storage sites. We present a new model of bubble (plume) dynamics, advection-dispersion of dissolved CO2, and carbonate chemistry. The focus is on a medium-sized CO2 release from 294 identified small point sources around Panarea Island (South-East Tyrrhenian Sea, Aeolian Islands, Italy) in water depths of about 40–50 m. This study evaluates how multiple CO2 seep sites generate a temporally variable plume of dissolved CO2. The model also allows the overall flow rate of CO2 to be estimated based on field measurements of pH. Simulations indicate a release of ∼6900 t y–1 of CO2 for the investigated area and highlight an important role of seeps located at >20 m water depth in the carbon budget of the Panarea offshore gas release system. This new transport-reaction model provides a framework for understanding potential future leaks from CO2 storage sites.

Continue reading ‘Simulating and quantifying multiple natural subsea CO2 seeps at Panarea Island (Aeolian Islands, Italy) as a proxy for potential leakage from subseabed carbon storage sites’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book