Posts Tagged 'vents'

Global change effects on seagrass ecosystem

Rising carbon dioxide (CO2) concentrations in the atmosphere will increase the average pCO2 level in the world oceans, which will have a knock-on effect on the marine ecosystem. Coastal seagrass communities one of the most productive marine ecosystems are predicted to benefit from the increase in CO2 levels, but long-term effects of elevated CO2 on seagrass communities are less understood. Population reconstruction techniques was used to investigate the population dynamics of Cymodocea nodosa meadows, exposed to long term elevated CO2 at volcanic seeps off Greece and Italy. Effect of elevated CO2 was noticed on the growth, morphometry, density, biomass and age structure at CO2 seeps. Above to below ground biomass ratio of C. nodosa were higher at CO2 seeps than at reference sites. The plastochrome interval were similar at all CO2 seeps. The shoot age and shoot longevity of plants were lower at seeps than reference sites. The present recruitment (sampled year) of the seagrass were higher than long-term average recruitment of the communities near the seeps. Carbon to nitrogen ratios (%DW) of C. nodosa were higher in leaves at seeps. Annual leaf production was higher near the seeps. This study suggests increased production of C. nodosa under elevated CO2 levels, but other co-factors such as nutrients, trace metal toxicity must also be taken into consideration while predicting effects of future CO2 concentrations. Volcanic CO2 seeps are now being used as natural analogues for ocean acidification studies although these areas can be affected by trace element input and may alter ecosystem responses to gradient in carbonate chemistry. Here Fe and a range of trace elements (Cd, Co, Cu, Hg, Mn, Pb, Ni and Zn) were analysed from sediments and from the roots, rhizomes and leaves of seagrass at six CO2 seeps and reference sites off Greece and Italy. There were higher metal levels in sediment and seagrasses at all CO2 seeps than reference sites. Sediment Quality Guideline Quotient, a commonly used pollution index, indicated that some of the metals (Cd, Cu, Hg, Ni) were in high enough concentrations to have adverse biological effects, such as Cu at Ischia site and Hg at Vulcano. Higher accumulation of elements from sediments in roots and leaves at CO2 seeps were found from Bio Sediment Accumulation Factor index. There were higher levels of Cu, Fe, Mn and Zn in leaves and rhizomes for P. oceanica and higher levels of Cd, Co, Cu, Fe and Zn in C. nodosa compartments at CO2 seeps. Fe and Mn were found with positive correlation within sediment-roots and sediment-rhizomes, whereas Cd, Co and Pb were found with positive correlation in compartments of C. nodosa. In P. oceanica positive correlation were only observed for Cd within sediment-roots and plant compartments. Low pH and ocean acidification increased the concentration of elements at CO2 seeps than reference sites. Thus, caution is needed, when using volcanic seep systems as analogue for the effects of rising CO2, as metals can reach levels that are toxic to seagrass, masking any potential benefits of increased levels of carbon dioxide for seagrass productivity. Net community production (NCP) and community respiration (CR) were measured under air exposed and CO2 enriched conditions for intertidal Z. noltei meadows and unvegetated sediment communities during emersion in summer and winter seasons. Community production and respiration were measured in-situ using benthic chambers. CO2 flux under air and CO2 enriched conditions were measured over a series of short term incubations (30min) using an infra-red gas analyser. Incident photosynthetic active radiation (PAR) was recorded during the incubations covering the daily and seasonal variation. Linear regression model was used to test the effects of irradiance on net community production. NCP of Z. noltei community were higher under CO2 enriched conditions than air exposed conditions in both summer and winter seasons. There was no effect of CO2 on the CR rate of Z. noltei community in summer season. NCP of sediment community were higher in summer season and winter season under CO2 enriched conditions. Sediment CR rates were higher in winter than summer season. The light compensation point of Z. noltei and sediment community were lower in both seasons under CO2 enriched conditions. Seasonal budget of community production was higher in Z. noltei than sediment communities. A clear effect of PAR was noticed on the net community production of both communities. Higher PAR intensities resulted in higher NCP under CO2 enriched conditions for both communities. CO2 enrichment will have a positive effect on the intertidal communities during emersion.

Continue reading ‘Global change effects on seagrass ecosystem’

Functional genomic analysis of corals from natural CO2‐seeps reveals core molecular responses involved in acclimatization to ocean acidification

Little is known about the potential for acclimatization or adaptation of corals to ocean acidification and even less about the molecular mechanisms underpinning these processes. Here, we examine global gene expression patterns in corals and their intracellular algal symbionts from two replicate population pairs in Papua New Guinea that have undergone long‐term acclimatization to natural variation in pCO2. In the coral host, only 61 genes were differentially expressed in response to pCO2environment, but the pattern of change was highly consistent between replicate populations, likely reflecting the core expression homeostasis response to ocean acidification. Functional annotations highlight lipid metabolism and a change in the stress response capacity of corals as key parts of this process. Specifically, constitutive downregulation of molecular chaperones was observed, which may impact response to combined climate change‐related stressors. Elevated CO2 has been hypothesized to benefit photosynthetic organisms but expression changes of in hospite Symbiodiniumin response to acidification were greater and less consistent among reef populations. This population‐specific response suggests hosts may need to adapt not only to an acidified environment, but also to changes in their Symbiodinium populations that may not be consistent among environments, adding another challenging dimension to the physiological process of coping with climate change.

Continue reading ‘Functional genomic analysis of corals from natural CO2‐seeps reveals core molecular responses involved in acclimatization to ocean acidification’

A comparison of life-history traits in calcifying Spirorbinae polychaetes living along natural pH gradients

Low-pH vent systems are ideal natural laboratories to study the consequences of long-term low-pH exposure on marine species and thus identify life-history traits associated with low-pH tolerance. This knowledge can help to inform predictions on which types of species may be less vulnerable in future ocean acidification (OA) scenarios. Accordingly, we investigated how traits of calcifying polychaete species (Serpulidae, Spirorbinae) varied with pH using a functional trait analysis at 2 natural pH gradients around the Castello Aragonese islet off Ischia, Italy. We first observed the distribution and abundance patterns of all calcifying polychaete epiphytes in the canopy of Posidonia oceanica seagrass across these gradients. We then used laboratory trials to compare fecundity, settlement success, and juvenile survival in the dominant species from a control (Pileolaria militaris Claparède, 1870) and a low-pH site (Simplaria sp.). We found significantly higher reproductive output, juvenile settlement rates, and juvenile survival in Simplaria sp. individuals from the low-pH site, compared to P. militaris individuals from control pH sites, when observed in their respective in situ pH conditions. Our results suggest that tolerance to low pH may result, in part, from traits associated with successful reproduction and rapid settlement under low-pH conditions. This finding implies that other species with similar life-history traits may respond similarly, and should be targeted for future OA tolerance research.

Continue reading ‘A comparison of life-history traits in calcifying Spirorbinae polychaetes living along natural pH gradients’

Effect of ocean acidification on primary producer in coastal environment: change of ecosystems in CO2 seeps (in Japanese)

Surface oceans absorb a part of anthropogenic CO2, and it induces changes in carbonate equilibrium of seawater. The seawater is gradually acidified, and saturation status of calcium carbonate is being lowered. These changes in carbonate chemistry would be serious threats for marine organisms (e.g., calcifying organisms). Ecosystems around submarine CO2 vents; CO2 seep, would be natural analogues of ocean acidification (OA) in coastal area, and ecosystem-level studies have been carried out so far. Drastic changes in species composition of primary producers have been reported in several CO2 seep. Common features are decrease in calcifying organisms such as coral and calcifying algae, and increase in mat-forming turf algae and seagrass. Considering such shift of benthic flora, change in primary production in coastal ecosystem is expected. However, there are limited number of direct measurements for photosynthesis, and their reports had focused on only some species living both in/out of CO2 seep. Therefore, the knowledges are limited to the physiological response of the primary producers to OA. In order to quantify the impact on the primary production at ecosystem level, consideration on the shift of flora and estimation per unit community area will be required.

Continue reading ‘Effect of ocean acidification on primary producer in coastal environment: change of ecosystems in CO2 seeps (in Japanese)’

Spiculosiphon oceana (Foraminifera) a new bio-indicator of acidic environments related to fluid emissions of the Zannone Hydrothermal Field (central Tyrrhenian Sea)

Highlights

• Benthic foraminifers calcification process sensitive to ocean acidification.
Spiculosiphon oceana a proxy of acidic environments.
• New record of a shallow-water hydrothermal field in the western Mediterranean Sea.

Abstract

The new record of a shallow-water submarine hydrothermal field (<150 m w.d.) in the western Mediterranean Sea (Tyrrhenian Sea, Italy) allows us to study CO2 fluid impact on benthic foraminifers. Benthic foraminifers calcification process is sensitive to ocean acidification and to local chemical and physical parameters of seawater and pore water. Thus, foraminifers can record specific environmental conditions related to hydrothermal fluids, but at present their response to such activity is poorly defined. The major outcome of this study is the finding of a very uncommon taxon for the Mediterranean Sea, i.e., the Spiculosiphon oceana, a giant foraminifer agglutinating spicules of sponges. This evidence, along with the strong decrease of calcareous tests in the foraminiferal assemblages associated to hydrothermal activity, provides new insights on the meiofauna living in natural stressed environment. In particular, observations obtained from this study allow us to consider S. oceana a potential tolerant species of high CO2 concentrations (about 2–4 times higher than the normal marine values) and a proxy of acidic environments as well as of recent ocean acidification processes.

Continue reading ‘Spiculosiphon oceana (Foraminifera) a new bio-indicator of acidic environments related to fluid emissions of the Zannone Hydrothermal Field (central Tyrrhenian Sea)’

Ocean acidification studies in coral reefs of Japan

Increasing anthropogenic CO2 emissions cause progressive ocean acidification, reducing the calcium carbonate saturation state and coral reef calcification rate. The future uptake of CO2 by the world ocean is predicted to reduce seawater pH by 0.3–0.5 units over the next few decades, which corresponds to a rate 100 times faster than that observed at any time during the last 20 million years. In this chapter, we discuss the effects of ocean acidification on coral reefs, which have been initially probed by culture experiments at several decreased pH conditions, being subsequently investigated by multiple stress factor experiments and field observations of acidified sites. By considering previous studies, we propose that the evaluation and prediction of future ecosystem dynamics require the development of convenient and inexpensive carbonate chemistry-related field measurement techniques such as pH logging, additionally highlighting the importance of studying two naturally acidified sites in Japan, namely, the Iwotorishima and Shikine Islands.

Continue reading ‘Ocean acidification studies in coral reefs of Japan’

Photosynthesis and mineralogy of Jania rubens at low pH/high pCO2: a future perspective

Highlights

• Calcifying red algae may show species-specific response to ocean acidification (OA).
• Photosynthesis and mineralogy (biosphere) were assessed after a three-week transplant.
• Field carbon chemistry (hydrosphere) and irradiance (atmosphere) were also considered.
• Photosynthesis decreased while calcification was maintained under future pH conditions.
• The calcifying Jania rubens may survive but reducing the fitness under OA.

Abstract

Corallinales (Rhodophyta) are high Mg-calcite macroalgae and are considered among the most vulnerable organisms to ocean acidification (OA). These sensitive species play fundamental roles in coastal systems as food source and settlement promoters as well as being involved in reef stabilization, and water carbonate balance. At present only a few studies are focused on erect calcifying macroalgae under low pH/high pCO2 and the contrasting results make difficult to predict the ecological consequences of the OA on the coralline algae. In this paper the physiological reasons behind the resistance of Jania rubens, one of the most common calcareous species, to changing ocean pH are analysed. In particular, we studied the photosynthetic and mineralogical response of J. rubens after a three-week transplant in a natural CO2 vent system. The overall results showed that J. rubens could be able to survive under predicted pH conditions even though with a reduced fitness; nevertheless physiological limits prevent the growth and survival of the species at pH 6.7. At low pH (i.e. pH 7.5), the maximum and effective PSII efficiency decreased even if the increase of Rubisco expression suggests a compensation effort of the species to cope with the decreased light-driven products. In these circumstances, a pH-driven bleaching phenomenon was also observed. Even though the photosynthesis decreased at low pH, J. rubens maintained unchanged the mineralogical composition and the carbonate content in the cell wall, suggesting that the calcification process may also have a physiological relevance in addition to a structural and/or a protective role. Further studies will confirm the hypotheses on the functional and evolutionary role of the calcification process in coralline algae and on the ecological consequences of the community composition changes under high pCO2 oceans.

Continue reading ‘Photosynthesis and mineralogy of Jania rubens at low pH/high pCO2: a future perspective’


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Ocean acidification in the IPCC AR5 WG II

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