Posts Tagged 'Mediterranean'

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’

Mapping of recent brachiopod microstructure: a tool for environmental studies

Shells of brachiopods are excellent archives for environmental reconstructions in the recent and distant past as their microstructure and geochemistry respond to climate and environmental forcings. We studied the morphology and size of the basic structural unit, the secondary layer fibre, of the shells of several extant brachiopod taxa to derive a model correlating microstructural patterns to environmental conditions. Twenty-one adult specimens of six recent brachiopod species adapted to different environmental conditions, from Antarctica, to New Zealand, to the Mediterranean Sea, were chosen for microstructural analysis using SEM, TEM and EBSD. We conclude that: 1) there is no significant difference in the shape and size of the fibres between ventral and dorsal valves, 2) there is an ontogenetic trend in the shape and size of the fibres, as they become larger, wider, and flatter with increasing age. This indicates that the fibrous layer produced in the later stages of growth, which is recommended by the literature to be the best material for geochemical analyses, has a different morphostructure and probably a lower organic content than that produced earlier in life. In two species of the same genus living in seawater with different temperature and carbonate saturation state, a relationship emerged between the microstructure and environmental conditions. Fibres of the polar Liothyrella uva tend to be smaller, rounder and less convex than those of the temperate Liothyrella neozelanica, suggesting a relationship between microstructural size, shell organic matter content, ambient seawater temperature and calcite saturation state.

Continue reading ‘Mapping of recent brachiopod microstructure: a tool for environmental studies’

Influence of ocean acidification on elemental mass balances and particulate organic matter stoichiometry in natural plankton communities  

The oceanic uptake of anthropogenic CO2 leads to a gradual acidification of the ocean. Ocean acidification (OA) is known to affect marine biota from the organism to the ecosystem level but with largely unknown consequences for the cycling of key elements such as carbon, nitrogen, and phosphorus. However, the ocean’s ability to absorb anthropogenic carbon or to provide sufficient food for humankind depends on these oceanic material cycles. This doctoral dissertation thus aimed to assess the influence of OA on biogeochemical cycles of elements in natural pelagic food webs of several trophic levels (up to fish larvae) over extended time scales of weeks to months. Large-scale pelagic mesocosms (up to 75 m3 per unit) were deployed in different marine ecosystems and new methods were developed to quantify the downward flux of particulate organic matter under simulated OA. This thesis reports on the potential influence of OA on element pool partitioning and particulate organic matter stoichiometry with consequences for biogeochemical cycling of elements in the ocean. Furthermore the potential and limitations of biogeochemical measurements inside pelagic mesocosms that host entire plankton communities are elucidated.

Continue reading ‘Influence of ocean acidification on elemental mass balances and particulate organic matter stoichiometry in natural plankton communities  ‘

Relationship between mineralogy and minor element partitioning in limpets from the Ischia CO2 vent site provides new insights into their biomineralization pathway

It has long since been noted that minor element (Me) partitioning into biogenic carbonates is sometimes different from Me partitioning into inorganically precipitated carbonates. The prime example is the partitioning coefficient, which might be lower or even higher than the one of inorganically precipitated carbonate. Such a difference is usually termed “vital effect” and is seen as indicative of a biologically modified minor element partitioning. Over the last three decades interest in conceptual biomineralization models compatible with minor element and isotope fractionation has been steadily increasing. However, inferring features of a biomineralization mechanism from Me partitioning is complicated, because not all partitioning coefficients show vital effects in every calcium carbonate producing organism. Moreover, the partitioning coefficient is not the only aspect of Me partitioning. Other aspects include polymorph specificity and rate dependence. Patellogastropod limpets are ideally suited for analysing Me partitioning in terms of biomineralization models, because they feature both aragonitic and calcitic shell parts, so that polymorph specificity can be tested. In this study, polymorph-specific partitioning of the minor elements Mg, Li, B, Sr, and U into shells of the patellogastropod limpet Patella caerulea from within and outside a CO2 vent site at Ischia (Italy) was investigated by means of LA-ICP-MS. The partitioning coefficients of U, B, Mg, and Sr (in aragonite) differed from the respective inorganic ones, while the partitioning coefficients of Li and Sr (in calcite) fell within the range of published values for inorganically precipitated carbonates. Polymorph specificity of Me partitioning was explicable in terms of inorganic precipitation in the case of Sr and Mg, but not Li and B. Seawater carbon chemistry did not have the effect on B partitioning that was expected on the basis of data on inorganic precipitates and foraminifera. Carbon chemistry did affect Mg (in aragonite) and Li, but only the effect on Mg was explicable in terms of calcification rate. On the one hand, these results show that Me partitioning in P. caerulea is incompatible with a direct precipitation of shell calcium carbonate from the extrapallial fluid. On the other hand, our results are compatible with precipitation from a microenvironment formed by the mantle. Such a microenvironment was proposed based on data other than Me partitioning. This is the first study which systematically employs a multi-element, multi-aspect approach to test the compatibility of Me partitioning with different conceptual biomineralization models.

Continue reading ‘Relationship between mineralogy and minor element partitioning in limpets from the Ischia CO2 vent site provides new insights into their biomineralization pathway’

Ocean acidification in the Middle East and North African region

After examining the current state of knowledge about ocean acidification in Middle East and North African (MENA) countries, we model the socio-economic impacts of disasters, ocean acidification and ecological risk. We use Extreme Value Theory and Peak Over Threshold concept to define the critical threshold point for ocean pH value as an Ornstein-Uhlenbeck process, initially with Gaussian noise. We define the benchmark pH based on time series observations which exhibit moderate to large variations and use Monte Carlo simulations and also model non-Gaussian cases to examine the probability of disasters.

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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)’

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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