Posts Tagged 'Mediterranean'

The carbonate system of the Eastern-most Mediterranean Sea, Levantine Sub-basin: variations and drivers

The carbonate system is a vital buffering system that controls the pH of seawater and maintains a healthy environment for marine organisms. As concerns regarding the fate of anthropogenic CO2 in the oceans are rising, it is becoming increasingly urgent to systematically quantify and understand this system’s parameters, particularly in heavily human-impacted areas, such as the Mediterranean Sea. To date, the paucity of time-series stations adopted to monitor the carbonate system in this sea has precluded characterizing the region at an adequate spatial resolution. Here, we present and study the seasonal and annual variability and drivers of the first carbonate system dataset collected for the Lebanese waters, monthly at the upper 80 m between 2012 and 2017 in two time-series stations offshore the North of Lebanon-Levantine Sub-basin, Eastern Mediterranean Sea. Annual trends were calculated for the non-adjusted and the adjusted carbonate system parameters (an adjustment that reduces the influence of simple-dilution-concentration [SDC] processes on the trends). Our results show high carbonate system inventory [total alkalinity (AT), total dissolved inorganic carbon (CT), and pH] compared to other Mediterranean areas. The obtained trends reflect increasing rates for both AT and CT, only significant at surface for CT(+5 ± 2 μmol kg−1.yr−1; p < 0.05). Whereas annual acidification rates were always significant (i.e. from −0.009 ± 0.004 to −0.0021 ± 0.001 pH units.yr−1at 0 m and in the upper 80 m respectively for pHT25adj). Concomitantly, decreasing trends of the saturation states for both CaCO3 minerals were calculated (−0.1 ± 0.04 and −0.07 ± 0.02 yr−1 for calcite and aragonite respectively at surface; p < 0.05). Moreover, our results showed that SDC processes, together with CO2 release/invasion and the active overturning circulation, are controlling this system in the Lebanese seawater, Eastern-most Mediterranean Sea. Contrariwise, the increasing trend of total alkalinity, mainly attributed to SDC processes (i.e. riverine inputs, weathering during extreme events, precipitations), may be buffering the observed acidification rate, which could have been worst in case AT in our area was lower.

Continue reading ‘The carbonate system of the Eastern-most Mediterranean Sea, Levantine Sub-basin: variations and drivers’

Living in future ocean acidification, physiological adaptive responses of the immune systems of sea urchins resident at a CO2 vent system

Highlights

• Paracentrotus lividus living at CO2 vents was compared to those at two control sites.
• Sea urchins are adapted to life at vent site by altering immune cells metabolism.
• Vent animals show a rearrangement of defensive abilities and antioxidant processes.

Abstract

The effects of ocean acidification, a major anthropogenic impact on marine life, have been mainly investigated in laboratory/mesocosm experiments. We used the CO2 vents at Ischia as a natural laboratory to study the long-term effects of ocean acidification on the sea urchin Paracentrotus lividus population resident in low-pH (7.8 ± 0.2) compared to that at two control sites (pH 8.02 ± 0.00; 8.02 ± 0.01). The novelty of the present study is the analysis of the sea urchin immune cells, the sentinels of environmental stress responses, by a wide-ranging approach, including cell morphology, biochemistry and proteomics. Immune cell proteomics showed that 311 proteins were differentially expressed in urchins across sites with a general shift towards antioxidant processes in the vent urchins. The vent urchin immune cells showed higher levels of total antioxidant capacity, up-regulation of phagosome and microsomal proteins, enzymes of ammonium metabolism, amino-acid degradation, and modulation of carbon metabolism proteins. Lipid-hydroperoxides and nitric oxide levels were not different in urchins from the different sites. No differences in the coelomic fluid pH, immune cell composition, animal respiration, nitrogen excretion and skeletal mineralogy were observed. Our results reveal the phenotypic plasticity of the immune system of sea urchins adapted to life at vent site, under conditions commensurate with near-future ocean acidification projections.

Continue reading ‘Living in future ocean acidification, physiological adaptive responses of the immune systems of sea urchins resident at a CO2 vent system’

Spatio-temporal distribution of physicochemical and bacteriological parameters in the north area of Monastir bay, eastern coast of Tunisia

Temporal characterization of physicochemical and bacteriological parameters of the Monastir bay was conducted out on 12 stations, during six sampling periods in 2014. Results showed a seasonal variation on the physicochemical parameters of the water masses (temperature, salinity, oxygen, pH, and turbidity) and well-oxygenated waters. Results indicated the absence of mineral phosphorus and the presence of low concentration of organic phosphorus in the stations close the coastline. Mineral nitrogen represented completely by nitrate, and organic nitrogen was detected everywhere during all sampling periods without any particular distribution. Chlorophyll-a concentrations present at low ratio characterizing an oligotrophic ecosystem showed two peaks, one during spring (April, May) and second in fall (September), and were significantly correlated with temperature (R2 = 0.82). Statistical analysis of different physicochemical parameters showed a correlation between temperature pH and oxygen. ANOVA tests showed a significant difference inter-sampling periods and between stations. Bacterial flora is dominated by halotolerant germs, which showed higher concentrations in the southern part of the studied area and are inversely correlated with salinity, turbidity, oxygen, and organic nitrogen (respectively R2 = − 0.62; − 0.79; − 0.84; − 0.72). The same evolution pattern was observed in mesophilic non-halo-obligate microflora. The Vibrionaceae concentration was correlated with water temperature and was within the standards for marine waters. Fecal coliform bacteria are absent in the studied area during all sampling periods. No particularity in water quality was noticed in this ecosystem, which characterized a good state. However, one can say that the collected data on physicochemical and bacteriological evolution can provide baseline information for assisting management of the Monastir bay, which represented a typical and important model of south Mediterranean Sea.

Continue reading ‘Spatio-temporal distribution of physicochemical and bacteriological parameters in the north area of Monastir bay, eastern coast of Tunisia’

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’

Intertidal Mediterranean coralline algae habitat is expecting a shift toward a reduced growth and a simplified associated fauna under climate change

Coralline algae represent the most important bioconstructors in the Mediterranean Sea and are currently impaired by the effects of climate change (CC), particularly by global warming and ocean acidification (OA). We studied the effects of these two drivers on Ellisolandia elongata, an intertidal coralline algae that is known to host a rich biodiversity of associated fauna. We cultured turfs of E. elongata in experimental conditions of increased temperature and OA (using the values of the IPCC scenario RCP- 8.5 expected for 2100: actual mean temperature +3°C and pH = 7.78), and estimated alteration of algal linear growth and community structure, focusing especially on peracarid crustaceans and annelids. Our findings revealed a decrease in linear growth, yet with no significant changes on structural integrity, and a simplification of associated community, in particular for peracarids. Our study contributes to understand community-level response to CC drivers, highlighting the vulnerability of the fauna associated to an important Mediterranean marine habitat.

Continue reading ‘Intertidal Mediterranean coralline algae habitat is expecting a shift toward a reduced growth and a simplified associated fauna under climate change’

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’

Ocean acidification affects somatic and otolith growth relationship in fish: evidence from an in situ study

Ocean acidification (OA) may have varied effects on fish eco-physiological responses. Most OA studies have been carried out in laboratory conditions without considering the in situ pCO2/pH variability documented for many marine coastal ecosystems. Using a standard otolith ageing technique, we assessed how in situ ocean acidification (ambient, versus end-of-century CO2 levels) can affect somatic and otolith growth, and their relationship in a coastal fish. Somatic and otolith growth rates of juveniles of the ocellated wrasse Symphodus ocellatus living off a Mediterranean CO2 seep increased at the high-pCO2 site. Also, we detected that slower-growing individuals living at ambient pCO2 levels tend to have larger otoliths at the same somatic length (i.e. higher relative size of otoliths to fish body length) than faster-growing conspecifics living under high pCO2 conditions, with this being attributable to the so-called ‘growth effect’. Our findings suggest the possibility of contrasting OA effects on fish fitness, with higher somatic growth rate and possibly higher survival associated with smaller relative size of otoliths that could impair fish auditory and vestibular sensitivity.

Continue reading ‘Ocean acidification affects somatic and otolith growth relationship in fish: evidence from an in situ study’


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