Posts Tagged 'Mediterranean'

Along-path evolution of biogeochemical and carbonate system properties in the Intermediate Water of the Western Mediterranean

A basin-scale oceanographic cruise (OCEANCERTAIN2015) was carried out in the Western Mediterranean (WMED) in summer 2015 to study the evolution of hydrological and biogeochemical properties of the most ubiquitous water mass of the Mediterranean Sea, the Intermediate Water (IW). IW is a relatively warm water mass, formed in the Eastern Mediterranean (EMED) and identified by a salinity maximum all over the basin. While it flows westward, toward and across the WMED, it gradually loses its characteristics. This study describes the along-path changes of thermohaline and biogeochemical properties of the IW in the WMED, trying to discriminate changes induced by mixing and changes induced by interior biogeochemical processes. In the first part of the path (from the Sicily Channel to the Tyrrhenian Sea), respiration in the IW interior was found to have a dominant role in determining its biogeochemical evolution. Afterward, when IW crosses regions of enhanced vertical dynamics (Ligurian Sea, Gulf of Lion and Catalan Sea), mixing with surrounding water masses becomes the primary process. In the final part of the investigated IW path (the Menorca-Mallorca region), the role of respiration is further masked by the effects of a complex circulation of IW, indicating that short-term sub-regional hydrological processes are important to define IW characteristics in the westernmost part of the investigated area. A pronounced along-path acidification was detected in IW, mainly due to remineralization of organic matter. This induced a shift of the carbonate equilibrium toward more acidic species and makes this water mass increasingly less adequate for an optimal growth of calcifying organisms. The carbonate buffering capacity also decreases as IW flows through the WMED, making it more exposed to the adverse effects of a decreasing pH. The present analysis indicates that IW evolution in the sub-basins of the WMED is currently driven by complex hydrological and biogeochemical processes, which could be differently impacted by coming climate changes, in particular considering expected increases of extreme meteorological events, mainly due to the warming of the Mediterranean basin.

Continue reading ‘Along-path evolution of biogeochemical and carbonate system properties in the Intermediate Water of the Western Mediterranean’

Severe coastal hypoxia interchange with ocean acidification: an experimental perturbation study on carbon and nutrient biogeochemistry

Normally atmospheric CO2 is the major driver of ocean acidification (OA); however, local discharge/degradation of organic matter (OM) and redox reactions can exacerbate OA in coastal areas. In this work we study the response of nutrient and carbon systems to pH decrease in relation to hydrographically induced intermittent characteristics and examine scenarios for future ocean acidification in a coastal system. Laboratory microcosm experiments were conducted using seawater and surface sediment collected from the deepest part of Elefsis Bay; the pH was constantly being monitored while CO2 gas addition was adjusted automatically. In Elefsis Bay surface pCO2 is already higher than global present atmospheric values, while near the bottom pCO2 reaches 1538 μatm and carbonate saturation states were calculated to be around 1.5. During the experiment, in more acidified conditions, limited alkalinity increase was observed and was correlated with the addition of bicarbonates and OM. Ammonium oxidation was decelerated and a nitrification mechanism was noticed, despite oxygen deficiency, paralleled by reduction of Mn-oxides. Phosphate was found significantly elevated for the first time in lower pH values, without reprecipitating after reoxygenation; this was linked with Fe(II) oxidation and Fe(III) reprecipitation without phosphate adsorption affecting both available dissolved phosphate and (dissolved inorganic nitrogen) DIN:DIP (dissolved inorganic phosphate)ratio.

Continue reading ‘Severe coastal hypoxia interchange with ocean acidification: an experimental perturbation study on carbon and nutrient biogeochemistry’

Adult exposure to acidified seawater influences sperm physiology in Mytilus galloprovincialis: Laboratory and in situ transplant experiments


•SWAc impacts on sperm physiology in the M. galloprovincialis after paternal exposure.

•Microcosm and in situ transplant experiment were set up and compared.

•Several sperm quality parameters were analyzed at different exposure times.

•Paternal SWAc exposure affects sperm motility, morphology, mitochondria and pHi.

•Microcosm experiments allowed to explore mechanism underlying responses to SWAc.


The ongoing increase of CO2 in the atmosphere is inducing a progressive lowering of marine water pH that is predicted to decrease to 7.8 by the end of this century. In marine environment, physical perturbation may affect reproduction, which is crucial for species’ survival and strictly depends on gamete quality. The effects of seawater acidification (SWAc) on gamete quality of broadcast spawning marine invertebrates result largely from experiments of gamete exposure while the SWAc impact in response to adult exposure is poorly investigated. Performing microcosm and in field experiments at a naturally acidified site, we investigated the effects of adult SWAc exposure on sperm quality parameters underlying fertilization in Mytilus galloprovincialis. These animals were exposed to pH 7.8 over 21 days and collected at different times to analyze sperm parameters as concentration, motility, viability, morphology, oxidative status, intra- and extra-cellular pH and mitochondrial membrane potential. Results obtained in the two experimental approaches were slightly different. Under field conditions, we found an increase in total sperm motility and mitochondrial membrane potential on days 7 and 14 from the start of SWAc exposure whereas, in microcosm, SWAc group showed an increase of total motility on day 14. In addition, sperm morphology and intracellular pH were affected in both experimental approaches; whereas oxidative stress was detected only in spermatozoa collected from mussels under natural SWAc. The overall analysis suggests that, in mussels, SWAc toxic mechanism in spermatozoa does not involve oxidative stress. This study represents the first report on mussel sperm quality impairment after adult SWAc exposure, which may affect fertilization success with negative ecological and economic consequences; it also indicates that, although naturally acidified areas represent ideal natural laboratories for investigating the impact of ocean acidification, microcosm experiments are necessary for examining action mechanisms.

Continue reading ‘Adult exposure to acidified seawater influences sperm physiology in Mytilus galloprovincialis: Laboratory and in situ transplant experiments’

Trace metal accumulation in the commercial mussel M. galloprovincialis under future climate change scenarios


•The increase in CO2 alone did not display biological or chemical changes in mussels.

•At 25 °C byssus strength and condition index of Galician mussel decreased.

•The increase in temperature amplified metal bioaccumulation in mussels.


The current trend of climatic alterations will accelerate the modification of the ocean system by, among other aspects, changing the metal speciation and its bioavailability which may have an impact in their accumulation by marine organisms. Understanding the impact of these potential changes is essential for future risk assessment of metal contamination. In the present study, we selected the species Mediterranean mussel (Mytilus galloprovincialis) as the main European aquaculture production bivalve and due to its widespread use for biomonitoring purposes. A long-term test (2 months) was carried out to explore the impact that global change in the marine environment (warming and CO2 increase) may exert on the accumulation of dissolved trace metals (Cu, Co, Pb, Cd, Cr, As and Ni) in different body parts of mussels (foot and soft tissue).

Studied mussels were collected at two different climatic locations (Atlantic and Mediterranean Sea) and exposed to unspiked, unpolluted seawater from the Vigo Ria (NW Iberian Peninsula). Results showed that under the global change conditions proposed in this study (1100 pCO2 and 25 °C), the increase in temperature resulted in a lower condition index and byssus strength for mussels from Atlantic Sea, while Mediterranean sea mussels, adapted to higher temperatures, did not show remarkable variations. According to trace metals accumulation in different body parts of the studied mussels, it was observed that the effect of increasing CO2 alone did not show to have an impact in the bioaccumulation, but the combined stressors (increase in CO2 and temperature) may lead to an increase in the bioaccumulation for some elements. The increase in temperature resulted in a decrease of the Cu content of foot tissue (byssus gland) in mussels from Atlantic Sea, which is in accordance with the lower byssus strength observed under such conditions. Our results indicate that the expected seawater temperature increase, which will be produced gradually during next decades, should be further study to ensure the species adaptability and aquaculture production.

Continue reading ‘Trace metal accumulation in the commercial mussel M. galloprovincialis under future climate change scenarios’

Estimation of rivers and coastal carbon fluxes in the Lebanese waters

Rivers and coastal waters transport carbon from continents to deep oceanic systems and act as important links in the carbon cycle. To the best of our knowledge, no studies have quantified the riverine and coastal carbon fluxes in the Lebanese waters, and hence this study aims to assess for the first time the carbon inputs in three major Lebanese rivers: Nahr Ibrahim, Nahr Damour and Nahr el Litani; and the coastal waters affected by their discharges. A monthly and seasonal sampling of key bio-physico-chemical parameters was conducted for Temperature, Salinity, pH, Dissolved Oxygen, Nitrates, Phosphates, Total Alkalinity (AT) and Dissolved inorganic Carbon (DIC), and subsequently the partial pressure of CO2 (pCO2) was derived according to the DOE handbook. The results show a clear seasonal variation of the physical parameters. The Alkalinity yield increased in all monitoring stations mostly in the river areas ranging from 0.24 to 1.8 mmol/L. DIC contribution to alkalinity is significant in rivers with relatively low alkalinity concentrations, and the DIC had a general opposite trend compared to AT; ranging from 57 and 39 mmol/L respectively. When computing the pCO2, the results show that the a range from 817 to 3283 µatm, higher than the atmospheric CO2 concentration showing that the studied rivers acted as a source for atmospheric CO2. This study can be considered as benchmark to understand the mechanisms of riverine-coastal ecosystem change and help the Lebanese community manage their coastal resources.

Continue reading ‘Estimation of rivers and coastal carbon fluxes in the Lebanese waters’

Effects of ocean acidification on phenology and epiphytes of the seagrass Posidonia oceanica at two CO2 vent systems of Ischia (Italy)

Morphological features of the seagrass Posidonia oceanica (L.) Delile and its epiphyte community were studied in three acidified stations located in two CO2 vents systems and one control station under normal pH conditions off the island of Ischia (Italy) to highlight the possible effects of ocean acidification. Plant phenology was analyzed every two months for a year cycle (June 2016–April 2017), while epiphytes were studied in the period of highest development of both the leaf canopy and the epiphytic community (June, August, and October 2016). The shoot density of Posidonia beds in the acidified stations of the studied sites was significantly higher than that in the control area. Significant differences in the mean leaf length according to the pH condition, month, and the interaction of these two factors were observed (PERMANOVA); the mean leaf width differed also among pH conditions and months. We recorded lower leaf lengths and widths in the acidified stations in all the considered months, compared to those in the control station. These differences are consistent with the higher impact of grazing by the herbivorous fish Sarpa salpa observed on the leaves in the acidified stations. However, the overall leaf surface available for epiphytes was similar among stations because of the higher shoot density under ocean acidification conditions. Overall, the composition and structure of the epiphytic community on the Posidonia leaves showed significant differences in relation to acidification: in both acidified sites, all the calcareous forms, both encrusting red algae (Corallinales) and animals (bryozoans, foraminiferans, and spirorbids), disappeared or were strongly reduced, in favor of encrusting or erect fleshy algae, and non-calcifying invertebrates (hydrozoans, tunicates) which dominated the assemblage. Coralline algae are early species in the epiphytic colonization of P. oceanica and therefore their absence can further modify the pattern of leaf colonization by other species. Therefore, the changes found in the epiphyte community in low pH areas could have potential cascading effects on the seagrass trophic network and the functioning of the system.

Continue reading ‘Effects of ocean acidification on phenology and epiphytes of the seagrass Posidonia oceanica at two CO2 vent systems of Ischia (Italy)’

Impacts of elevated pCO2 on Mediterranean mussel (Mytilus galloprovincialis): metal bioaccumulation, physiological and cellular parameters


• Elevated pCO2 did not impact 110mAg bioconcentration in juvenile and adult mussels.

• Seawater acidification increased 109Cd bioconcentration in juvenile mussels but not in adults.

• Eighty-two days of elevated pCO2 decreased feeding rate and haemocyte survival.

• Lysosomal membrane stability in mussels remained unaffected by elevated pCO2.

• Circulating cell-free protein and nucleic acids (ccf-DNA, ccf-RNA, ccf-miRNA) levels in mussels were not impacted by seawater acidification.


Ocean acidification alters physiology, acid-base balance and metabolic activity in marine animals. Accordingly, near future elevated pCO2 conditions could be expected to influence the bioaccumulation of metals, feeding rate and immune parameters in marine mussels. To better understand such impairments, a series of laboratory-controlled experiment was conducted by using a model marine mussel, Mytilus galloprovincialis. The mussels were exposed to three pH conditions according to the projected CO2 emissions in the near future (one ambient: 8.10 and two reduced: 7.80 and 7.50). At first, the bioconcentration of Ag and Cd was studied in both juvenile (2.5 cm) and adult (5.1 cm) mussels by using a highly sensitive radiotracer method (110mAg and 109Cd). The uptake and depuration kinetics were followed 21 and 30 days, respectively. The biokinetic experiments demonstrated that the effect of ocean acidification on bioconcentration was metal-specific and size-specific. The uptake, depuration and tissue distribution of 110mAg were not affected by elevated pCO2 in both juvenile and adult mussels, whereas 109Cd uptake significantly increased with decreasing pH in juveniles but not in adults. Regardless of pH, 110mAg accumulated more efficiently in juvenile mussels than adult mussels. After executing the biokinetic experiment, the perturbation was sustained by using the same mussels and the same experimental set-up, which enabled us to determine filtration rate, haemocyte viability, lysosomal membrane stability, circulating cell-free nucleic acids (ccf-NAs) and protein (ccf-protein) levels. The filtration rate and haemocyte viability gradually decreased by increasing the pCO2 level, whereas the lysosomal membrane stability, ccf-NAs, and ccf-protein levels remained unchanged in the mussels exposed to elevated pCO2 condition for eighty-two days. Considering these, this study suggests that acidified seawater partially shift metal bioaccumulation, physiological and cellular parameters in the mussel Mytilus galloprovincialis.

Continue reading ‘Impacts of elevated pCO2 on Mediterranean mussel (Mytilus galloprovincialis): metal bioaccumulation, physiological and cellular parameters’

Exposure to decreased pH and caffeine affects hemocyte parameters in the mussel Mytilus galloprovincialis

Combined effects of reduced pH, as predicted under climate change scenarios, and the most popular and widely used stimulant caffeine were assessed in hemocyte parameters of the mussel Mytilus galloprovincialis, being hemocytes involved in immune defense. Bivalves were exposed for one week to natural pH (8.1) and two reduced pH values (pH -0.4 units and pH -0.7 units). Exposure continued for additional two weeks, both in the absence and in the presence of environmentally relevant concentrations of caffeine (0.05 and 0.5 µg/L). Hemocyte parameters (total hemocyte count, hemocyte volume and diameter, neutral red uptake and hemocyte proliferation) were measured after 7 days of exposure to pH only, and after 14 (T1) and 21 (T2) days of exposure to the various pH*caffeine combinations. At all sampling times, pH significantly affected all the biological variables considered, whereas caffeine exhibited a significant influence at T2 only. Among the various hemocyte parameters, caffeine caused a significant increase in total hemocyte count at T2, and in hemocyte volume and diameter at both T1 and T2, when a significant interaction between pH and caffeine was also found. Overall, results demonstrated that hemocyte functionality was strongly influenced by the experimental conditions tested. Further studies are needed to assess combined effects of climate changes and emerging contaminants on bivalve immune system when challenged with environmental pathogens.

Continue reading ‘Exposure to decreased pH and caffeine affects hemocyte parameters in the mussel Mytilus galloprovincialis’

Resistance of seagrass habitats to ocean acidification via altered interactions in a tri-trophic chain

Despite the wide knowledge about prevalent effects of ocean acidification on single species, the consequences on species interactions that may promote or prevent habitat shifts are still poorly understood. Using natural CO2 vents, we investigated changes in a key tri-trophic chain embedded within all its natural complexity in seagrass systems. We found that seagrass habitats remain stable at vents despite the changes in their tri-trophic components. Under high pCO2, the feeding of a key herbivore (sea urchin) on a less palatable seagrass and its associated epiphytes decreased, whereas the feeding on higher-palatable green algae increased. We also observed a doubled density of a predatory wrasse under acidified conditions. Bottom-up CO2 effects interact with top-down control by predators to maintain the abundance of sea urchin populations under ambient and acidified conditions. The weakened urchin herbivory on a seagrass that was subjected to an intense fish herbivory at vents compensates the overall herbivory pressure on the habitat-forming seagrass. Overall plasticity of the studied system components may contribute to prevent habitat loss and to stabilize the system under acidified conditions. Thus, preserving the network of species interactions in seagrass ecosystems may help to minimize the impacts of ocean acidification in near-future oceans.

Continue reading ‘Resistance of seagrass habitats to ocean acidification via altered interactions in a tri-trophic chain’

Patterns in microbiome composition differ with ocean acidification in anatomic compartments of the Mediterranean coral Astroides calycularis living at CO2 vents


• Coral microbiomes contribute to host acclimatization to environmental change.

• Natural CO2 gradients are a model of global change-induced ocean acidification.

• Non-symbiotic coral Astroides calycularis survives in a natural acidified site.

• Calycularis mucus microbiome is the most affected by low pH conditions.

• Low pH conditions induce changes in microbiome supporting nitrogen cycling.


Coral microbiomes, the complex microbial communities associated with the different anatomic compartments of the coral, provide important functions for the host’s survival, such as nutrient cycling at the host’s surface, prevention of pathogens colonization, and promotion of nutrient uptake. Microbiomes are generally referred to as plastic entities, able to adapt their composition and functionality in response to environmental change, with a possible impact on coral acclimatization to phenomena related to climate change, such as ocean acidification. Ocean sites characterized by natural gradients of pCO2 provide models for investigating the ability of marine organisms to acclimatize to decreasing seawater pH. Here we compared the microbiome of the temperate, shallow water, non-symbiotic solitary coral Astroides calycularis that naturally lives at a volcanic CO2 vent in Ischia Island (Naples, Italy), with that of corals living in non-acidified sites at the same island. Bacterial DNA associated with the different anatomic compartments (mucus, tissue and skeleton) of A. calycularis was differentially extracted and a total of 68 samples were analyzed by 16S rRNA gene sequencing. In terms of phylogenetic composition, the microbiomes associated with the different coral anatomic compartments were different from each other and from the microbial communities of the surrounding seawater. Of all the anatomic compartments, the mucus-associated microbiome differed the most between the control and acidified sites. The differences detected in the microbial communities associated to the three anatomic compartments included a general increase in subdominant bacterial groups, some of which are known to be involved in different stages of the nitrogen cycle, such as potential nitrogen fixing bacteria and bacteria able to degrade organic nitrogen. Our data therefore suggests a potential increase of nitrogen fixation and recycling in A. calycularis living close to the CO2 vent system.

Continue reading ‘Patterns in microbiome composition differ with ocean acidification in anatomic compartments of the Mediterranean coral Astroides calycularis living at CO2 vents’

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Ocean acidification in the IPCC AR5 WG II

OUP book