Posts Tagged 'vents'

Plant and sediment properties in seagrass meadows from two Mediterranean CO2 vents: Implications for carbon storage capacity of acidified oceans

Highlights
• Seagrass features differed between control and low pH stations inconsistently in the two vents.

• Carbon content and its surficial accumulation decreased at high pCO2–low pH conditions.

• Carbon storage capacity of the seagrass may not increase at high pCO2-low pH conditions.

Abstract
Assessing the status of important carbon sinks such as seagrass meadows is of primary importance when dealing with potential climate change mitigation strategies. This study examined plant and sediment properties in seagrass meadows (Cymodocea nodosa (Ucria) Asch.) from two high pCO2–low pH Mediterranean vent systems, located at Milos (Greece) and Vulcano (Italy) Islands, providing insights on carbon storage potential in future acidified oceans. Contrary to what has been suggested, carbon content (both inorganic and organic) and its surficial accumulation decreased at high pCO2–low pH in comparison with controls. The decrease in inorganic carbon may result from the higher solubility of carbonates due to the more acidic conditions. At Vulcano, the seagrass properties (e.g., leaf area, biomass) appeared negatively affected by environmental conditions at high pCO2–low pH conditions and this may have had a detrimental effect on the organic carbon content and accumulation. At Milos, organic carbon decreased at high pCO2–low pH conditions, despite the increase in seagrass aboveground biomass, leaf length and area, probably as a consequence of site-specific features, which need further investigation and may include both biotic and abiotic factors (e.g., oligotrophic conditions, decreased sedimentation rate and input of allochthonous material). Results suggest that, in contrast to previous predictions based exclusively on the expected positive response of seagrasses to ocean acidification, carbon storage capacity of the seagrass C. nodosa may not increase at high pCO2-low pH conditions. This study emphasizes the need to investigate further the potential alteration in the climate mitigation service delivered by seagrass meadows in acidified oceans.

Continue reading ‘Plant and sediment properties in seagrass meadows from two Mediterranean CO2 vents: Implications for carbon storage capacity of acidified oceans’

Greenhouse gases, nutrients and the carbonate system in the Reloncaví Fjord (Northern Chilean Patagonia): implications on aquaculture of the mussel, Mytilus chilensis, during an episodic volcanic eruption

Highlights
• A large bloom of phytoplankton was detected in the surface waters of the Reloncaví fjord following the Calbuco volcano eruption.

• Subsequent to the Calbuco volcano eruption, higher N2O, CH4 and SO42− concentrations were observed in Fjord surface waters close to areas of river discharge.

• Optimal juvenile mussel growth was observed in refugee subsurface depths coinciding with increased aragonite saturation.

• Thus, the observed trends in the carbonate system and nutrient outputs may be valuable for developing effective management strategies for mussel aquaculture in the Reloncaví Fjord.

Abstract
This study investigates the immediate and mid-term effects of the biogeochemical variables input into the Reloncaví fjord (41°40′S; 72°23′O) as a result of the eruption of Calbuco volcano. Reloncaví is an estuarine system supporting one of the largest mussels farming production within Northern Chilean-Patagonia. Field-surveys were conducted immediately after the volcanic eruption (23–30 April 2015), one month (May 2015), and five months posterior to the event (September 2015). Water samples were collected from three stations along the fjord to determine greenhouse gases [GHG: methane (CH4), nitrous oxide (N2O)], nutrients [NO3−, NO2−, PO43−, Si(OH)4, sulphate (SO42−)], and carbonate systems parameters [total pH (pHT), temperature, salinity, dissolved oxygen (O2), and total alkalinity (AT)]. Additionally, the impact of physicochemical changes in the water column on juveniles of the produced Chilean blue mussel, Mytilus chilensis, was also studied. Following the eruption, a large phytoplankton bloom led to an increase in pHT, due to the uptake of dissolved-inorganic carbon in photic waters, potentially associated with the runoff of continental soil covered in volcanic ash. Indeed, high surface SO42− and GHG were observed to be associated with river discharges. No direct evidence of the eruption was observed within the carbonate system. Notwithstanding, a vertical pattern was observed, with an undersaturation of aragonite (ΩAr < 1) both in brackish surface (10 m), and saturated values in subsurface waters (3 to 7 m). Simultaneously, juvenile mussel shells showed maximized length and weight at 4 m depth. Results suggest a localized impact of the volcanic eruption on surface GHG, nutrients and short-term effects on the carbonate system. Optimal conditions for mussel calcification were identified within a subsurface refuge in the fjord. These specific attributes can be integrated into adaptation strategies by the mussel aquaculture industry to confront ocean acidification and changing runoff conditions.

Continue reading ‘Greenhouse gases, nutrients and the carbonate system in the Reloncaví Fjord (Northern Chilean Patagonia): implications on aquaculture of the mussel, Mytilus chilensis, during an episodic volcanic eruption’

A triple trophic boost: how carbon emissions indirectly change a marine food chain

The pervasive enrichment of CO2 in our oceans is a well‐documented stressor to marine life. Yet, there is little understanding about how CO2 affects species indirectly in naturally complex communities. Using natural CO2 vents, we investigated the indirect effects of CO2 enrichment through a marine food chain. We show how CO2 boosted the biomass of three trophic levels: from the primary producers (algae), through to their grazers (gastropods), and finally through to their predators (fish). We also found that consumption by both grazers and predators intensified under CO2 enrichment, but, ultimately, this top‐down control failed to compensate for the boosted biomass of both primary producers and herbivores (bottom‐up control). Our study suggests that indirect effects can buffer the ubiquitous and direct, negative effects of CO2 enrichment by allowing the upward propagation of resources through the food chain. Maintaining the natural complexity of food webs in our ocean communities could, therefore, help minimize the future impacts of CO2 enrichment.

Continue reading ‘A triple trophic boost: how carbon emissions indirectly change a marine food chain’

Biogenic habitat shifts under long-term ocean acidification show nonlinear community responses and unbalanced functions of associated invertebrates

Experiments have shown that increasing dissolved CO2 concentrations (i.e. Ocean Acidification, OA) in marine ecosystems may act as nutrient for primary producers (e.g. fleshy algae) or a stressor for calcifying species (e.g., coralline algae, corals, molluscs). For the first time, rapid habitat dominance shifts and altered competitive replacement from a reef-forming to a non-reef-forming biogenic habitat were documented over one-year exposure to low pH/high CO2 through a transplant experiment off Vulcano Island CO2 seeps (NE Sicily, Italy). Ocean acidification decreased vermetid reefs complexity via a reduction in the reef-building species density, boosted canopy macroalgae and led to changes in composition, structure and functional diversity of the associated benthic assemblages. OA effects on invertebrate richness and abundance were nonlinear, being maximal at intermediate complexity levels of vermetid reefs and canopy forming algae. Abundance of higher order consumers (e.g. carnivores, suspension feeders) decreased under elevated CO2 levels. Herbivores were non-linearly related to OA conditions, with increasing competitive release only of minor intertidal grazers (e.g. amphipods) under elevated CO2 levels.
Our results support the dual role of CO2 (as a stressor and as a resource) in disrupting the state of rocky shore communities, and raise specific concerns about the future of intertidal reef ecosystem under increasing CO2 emissions. We contribute to inform predictions of the complex and nonlinear community effects of OA on biogenic habitats, but at the same time encourage the use of multiple natural CO2 gradients in providing quantitative data on changing community responses to long-term CO2 exposure.

Continue reading ‘Biogenic habitat shifts under long-term ocean acidification show nonlinear community responses and unbalanced functions of associated invertebrates’

The influence of CO2 seeps to coastal environments of Shikine Island in Japan as indicated by geochemistry analyses of seafloor sediments

Recently, two shallow CO2 seeps were described in Ashitsuki and Mikama Bay (Shikine Island, Japan). These sites were deemed to have potentials for studying the impacts of ocean acidification. Here, we report geochemistry analyses of seawater and seafloor sediments collected from the shallow coasts on and around the two CO2 seeps. Seawater analyses indicated that shallow waters in the area share similar acidic characteristics (e.g. Avg. pH = ca. 7.1), supporting the result of a previous study. Next, the sediments from all sampling loci also share similar properties (Avg. Fe: Si = 0.043; Avg. organic content = 1.26%; Avg. relative Si content = 75.25%). However, sediments from Matsugashitamiyabi hot spring, which is located near the Ashitsuki seep, showed high Fe: Si ratio (1.250) when compared to other loci. This is most likely a local phenomenon, where iron accumulates in the sediment by the precipitation of rust produced through the mixing of FeS from the hot spring and carbonated seawater of the nearby CO2 seeps. We also compared seawater (e.g. Avg. pH = 8.3) and sediments (Avg. Fe: Si = 0.126; Avg. organic content = 2.06%; Avg. Si = 69.06%) of Hidaka Port in central Wakayama (as a standard sample of coastal surface water environment), to the Shikine Island samples excluding the Matsugashitamiyabi hot spring samples. The differences in characteristics (i.e. lower seawater pH and lower Avg. Fe: Si ratio of the latter) were probably caused by CO2 seep influence, and indicate that the influence of the hot spring water to the sediment of both CO2 seeps was minimal, or probably none. Accordingly, these seep sites are useful for future studies on the effects of ocean acidification on sea floor sediment composition, and its implication to biodiversity and the ecosystem.

Continue reading ‘The influence of CO2 seeps to coastal environments of Shikine Island in Japan as indicated by geochemistry analyses of seafloor sediments’

Fates of vent CO2 and its impact on carbonate chemistry in the shallow-water hydrothermal field offshore Kueishantao Islet, NE Taiwan

Highlights

• CO2 dissolution and fluid entrainment shape carbonate chemistry in vertical plumes.
• Fluids in the near-vent area have a short flushing time (tens of minutes).
• Mixing of vent fluids with seawater acts to retain vent carbon in ocean.

Abstract

Increasing public awareness of anthropogenic CO2 emissions and consequent global change has stimulated the development of pragmatic approaches for the study of shallow-water CO2 vents and seeps as natural laboratories of CO2 perturbations. How CO2 propagates from the emission sites into surrounding environments (ocean and atmosphere), and its effects on seawater carbonate chemistry, have never been studied from a mechanistic perspective. Here, we combine experimental and modeling approaches to investigate the carbonate chemistry of a shallow-water hydrothermal field offshore Kueishantao Islet, NE Taiwan. A simple Si-based mixing model is used to trace hydrothermal fluid mixing with seawater along convection pathways. The estimated vent fluid component in the near-vent region is generally <1%. We further employed a modified bubble-plume model to examine gas bubble-aqueous phase interaction. We explain the dissolved inorganic carbon characteristics of the vertical plume as a synergistic interaction between CO2 gas dissolution and fluid entrainment. The bubble-plume model provides a conservative estimate of the flushing time (tens of minutes) for water in the near-vent region. The acidic, dissolved inorganic carbon-rich water in the lateral buoyant plume readily releases CO2, but mixing with seawater rapidly quenches its degassing potential, so that hydrothermal carbon is retained in the ocean. Ebullition, governed by initial bubble size distribution, is the key mechanism for vent CO2 to exit the seawater carbonate system.

Continue reading ‘Fates of vent CO2 and its impact on carbonate chemistry in the shallow-water hydrothermal field offshore Kueishantao Islet, NE Taiwan’

Effects of short-term and long-term exposure to ocean acidification on carbonic anhydrase activity and morphometric characteristics in the invasive polychaete Branchiomma boholense (Annelida: Sabellidae): a case-study from a CO2 vent system

Highlights
• Carbonic anhydrase activity remained unchanged after 30-days exposure to high pCO2.

• A significant decrease in weight was observed under short-term acclimatization to low pH.

• Enzyme activity and protein content showed a 50% increase under chronic exposure to OA.

• A significant variation in wet weight was detected under long-term exposure to low pH.

Abstract
The aim of this study was to test the effects of short- and long-term exposure to high pCO2 on the invasive polychaete Branchiomma boholense (Grube, 1878), (Sabellidae), through the implementation of a transplant experiment at the CO2 vents of the Castello Aragonese at the island of Ischia (Italy). Analysis of carbonic anhydrase (CA) activity, protein tissue content and morphometric characteristics were performed on transplanted individuals (short-term exposure) as well as on specimens resident to both normal and low pH/high pCO2 environments (long-term exposure). Results obtained on transplanted worms showed no significant differences in CA activity between individuals exposed to control and acidified conditions, while a decrease in weight was observed under short-term acclimatization to both control and low pH, although at low pH the decrease was more pronounced (∼20%). As regard individuals living under chronic exposure to high pCO2, the morphometric results revealed a significantly lower (70%) wet weight of specimens from the vents with respect to animals living in high pH/low pCO2 areas. Moreover, individuals living in the Castello vents showed doubled values of enzymatic activity and a significantly higher (50%) protein tissue content compared to specimens native from normal pH/low pCO2. The results of this study demonstrated that B. boholense is inclined to maintain a great homeostatic capacity when exposed to low pH, although likely at the energetic expense of other physiological processes such as growth, especially under chronic exposure to high pCO2.

Continue reading ‘Effects of short-term and long-term exposure to ocean acidification on carbonic anhydrase activity and morphometric characteristics in the invasive polychaete Branchiomma boholense (Annelida: Sabellidae): a case-study from a CO2 vent system’


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Ocean acidification in the IPCC AR5 WG II

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