Posts Tagged 'Mediterranean'

Simulation of coastal processes affecting pH with impacts on carbon and nutrient biogeochemistry

Naturally occurring microbial decomposition of organic matter (OM) in coastal marine environments cause increased acidity in deeper layers similar or even exceeding the future predictions for global ocean acidification (OA). Experimental studies in coastal areas characterized by increased inputs of OM and nutrients, coping with intermittent hypoxic/anoxic conditions, provide decrease. Laboratory CO2-manipulated microcosm experiments were conducted using seawater and surface sediment collected from thdecrease. Labouratory CO2-manipulated microcosm experiments were conducted using seawater and surface sediment collected form the deepest part of Elefsis Bay (Saronikos Gulf, Eastern Mediterranean) focusing to study the co-evolution of processes affected by the decline of dissolved oxygen and pH induced by (a) OM remineralization and (b) the future anthropogenic increase of atmospheric CO2. Under more acidified conditions, a significant increase of total alkalinity was observed partially attributed to the sedimentary carbonate dissolution and the reactive nitrogen species shift towards ammonium. Nitrate and nitrite decline, in parallel with ammonium increase, demonstrated a deceleration of ammonium oxidation processes along with decrease in nitrate production. The decreased DIN:DIP ratio, the prevalence of organic nutrient species against the inorganic ones, the observations of constrained DON degradation and nitrate production decline and the higher DOC concentrations revealed the possible inhibition of OM decomposition under lower pH values. Finally, our results highlight the need for detailed studies of the carbonate system in coastal areas dominated by hypoxic/anoxic conditions, accompanied by other biogeochemical parameters and properly designed experiments to elucidate the processes sequence or alterations due to pH reduction.

Continue reading ‘Simulation of coastal processes affecting pH with impacts on carbon and nutrient biogeochemistry’

Physiological responses of the Mediterranean subtidal alga Peyssonnelia squamaria to elevated CO2

The ecological consequences of ocean acidification are unclear due to varying physiological properties of macroalgae and species-specific responses. Therefore, in the present study, we used a laboratory culture experiment to analyse the eco-physiological responses of the Mediterranean subtidal red alga Peyssonnelia squamaria to CO2-induced lower pH. Our results showed an increase in the photosynthetic performance and growth rate of P. squamaria, despite the reduction in CaCO3 content in the low pH treatment. According to our results, we believe that samples exposed to elevated CO2 could be regulated own nitrogen metabolism to support increased growth rate and it may be down-regulated nitrate uptake. As a result, we hypothesize that P. squamaria may benefit from ocean acidification.

Continue reading ‘Physiological responses of the Mediterranean subtidal alga Peyssonnelia squamaria to elevated CO2’

Emiliania huxleyi coccolith calcite mass modulation by morphological changes and ecology in the Mediterranean Sea

To understand the response of marine calcifying organisms under high CO2 scenarios, it is critical to study their calcification patterns in the natural environment. This paper focuses on a major calcifying phytoplankton group, the coccolithophores, through the analysis of water samples collected along a W-E Mediterranean transect during two research cruises, in April 2011 (Meteor cruise M84/3) and May 2013 (MedSeA cruise 2013). The Mediterranean Sea is a marginal sea characterized by large biogeochemical gradients. Currently, it is undergoing both warming and ocean acidification, processes which are rapidly modifying species distribution and calcification. The species Emiliania huxleyi largely dominates the total coccolithophore production in present day oceans and marine basins, including the Mediterranean Sea. A series of morphometric measurements were performed on the coccoliths of this species to estimate their mass, length and calculate a calcification index (proxy for the size-normalized calcification degree). The most abundant morphotype of E. huxleyi in the Mediterranean Sea is Type A. Coccoliths of this morphotype were additionally analyzed based on scanning electron microscopy images: four calcification varieties were quantified, according to the relationship between slit length-tube width, and the state of the central area (open or closed). The average E. huxleyi coccolith mass along the Mediterranean oceanographic transect depended strongly on both the average coccolith length and calcification index. The variability in average coccolith length and calcification index across samples reflected oscillations in the relative abundance of the calcification varieties. We also demonstrated that the distribution of the calcification varieties followed the main environmental gradients (carbonate chemistry, salinity, temperature, nutrient concentrations). Hence, shifts in the distribution of the calcification varieties and of the average E. huxleyi coccolith mass are to be expected in the Mediterranean Sea under climate change. These physiological and ecological responses will modulate the net coccolithophore calcification and, ultimately, the regional carbonate export to the seafloor.

Continue reading ‘Emiliania huxleyi coccolith calcite mass modulation by morphological changes and ecology in the Mediterranean Sea’

Effects of ocean acidification on 109Cd, 57Co, and 134Cs bioconcentration by the European oyster (Ostrea edulis): Biokinetics and tissue-to-subcellular partitioning


• A decrease in pH does not affect the uptake kinetics of 109Cd and 57Co, nor the   depuration of 109Cd and 134Cs.
• Depuration kinetics of 57Co is modified as pC02 conditions change.
• No variation in the subcellular sequestration of these three trace elements under low pH conditions.
• A systematic bleaching of the oyster shells was observed with a drop in pH over 40 days.


The uptake and depuration kinetics of dissolved 109Cd, 57Co and 134Cs were determined experimentally in the European flat oyster Ostrea edulis (Linnaeus, 1758) under different pH conditions (i.e., 8.1, 7.8 and 7.5) for 59 days. Uptake and depuration rates were variable within these elements; no effects were observed under different pH conditions for the uptake biokinetics of 109Cd and 57Co and depuration of 109Cd and 134Cs in oyster. The uptake and depuration rate constants of 134Cs differed during the exposure phase between treatments, while the steady state concentration factors (CFss) were similar. The resulting Cs activity that was purged during short- and long-term depuration phases differed, while the remaining activities after thirty-nine days depuration phase (RA39d) were similar. Co-57 depuration was affected by pCO2 conditions: RA39d were found to be significantly higher in oysters reared in normocapnia (pCO2 = 350 μatm) compared to high pCO2 conditions. Co-57 tissue distribution did not differ among the variable pCO2 conditions, while 109Cd and 134Cs accumulated in soft tissue of oysters were found to be higher under the highest pCO2. Additionally, Cd, Co and Cs were stored differently in various compartments of the oyster cells, i.e. cellular debris, metal-rich granules (MRG) and metallothionein-like proteins (MTLP), respectively. The subcellular sequestration of the elements at the end of the depuration phase did not differ among pH treatments. These results suggest that bioconcentration and tissue/subcellular distribution are element-specific in the oyster, and the effects of higher pCO2 driven acidification and/or coastal acidification variably influence these processes.

Continue reading ‘Effects of ocean acidification on 109Cd, 57Co, and 134Cs bioconcentration by the European oyster (Ostrea edulis): Biokinetics and tissue-to-subcellular partitioning’

Coccolithophore community response along a natural CO2 gradient off Methana (SW Saronikos Gulf, Greece, NE Mediterranean)

A natural pH gradient caused by marine CO2 seeps off the Methana peninsula (Saronikos Gulf, eastern Peloponnese peninsula) was used as a natural laboratory to assess potential effects of ocean acidification on coccolithophores. Coccolithophore communities were therefore investigated in plankton samples collected during September 2011, September 2016 and March 2017. The recorded cell concentrations were up to ~50 x103 cells/l, with a high Shannon index of up to 2.8, along a pH gradient from 7.61 to 8.18, with values being occasionally <7. Numerous holococcolithophore species represented 60–90% of the surface water assemblages in most samples during September samplings. Emiliania huxleyi was present only in low relative abundances in September samples, but it dominated in March assemblages. Neither malformed nor corroded coccolithophores were documented. Changes in the community structure can possibly be related to increased temperatures, while the overall trend associates low pH values with high cell densities. Our preliminary results indicate that in long-termed acidified, warm and stratified conditions, the study of the total coccolithophore assemblage may prove useful to recognize the intercommunity variability, which favors the increment of lightly calcified species such as holococcolithophores.

Continue reading ‘Coccolithophore community response along a natural CO2 gradient off Methana (SW Saronikos Gulf, Greece, NE Mediterranean)’

Climate change impacts on the biota and on vulnerable habitats of the deep Mediterranean Sea

Deep sea is the largest and likely the most biologically diverse ecosystem of the world, but it is also the most unknown. The Mediterranean Sea (< 1% of the ocean surface and contains only the 0.3% of its volume) is a hot spot of marine biodiversity containing ca 7.5% of the world marine biodiversity, associated with a multitude of habitats spreading from the coast to its dark portion (e.g., coral banks, seamounts, canyons, and hydrothermal vents). Its deep-sea ecosystems are increasingly subjected to direct anthropogenic impacts (including overfishing, chemical pollution, dumping, litter, and plastics), which are often over-imposed to the increasing effects of global change. Here, are illustrated the expected impacts of shifts in the main variables such as temperature, food supply, pH, and oxygen on the deep Mediterranean Sea ecosystems. One of the most consequences is related to shifts in the quality and quantity of the inputs of organic matter to the deep seafloor. The deep Mediterranean Sea is far more oligotrophic than other oceans at equal depths, and although deep-sea biota reacts to food shortage by increasing their efficiency in its use, a decrease in food availability can have dramatic effects on its food webs. The deep Mediterranean Sea is showing a clear rise of deep-water temperatures. In the last decades, deep-water warming is accelerating at unprecedented rates, causing a significant shift in biodiversity even for variations in the order of 0.1 °C. Higher temperatures increase deep-sea metabolism, thus exacerbating the effects of food limitation. Moreover, ocean acidification reduces the calcification capacity of corals and alters their metabolism. Although it can be expected that increasing temperatures might increase the potential spread of oxygen minimum zone, so far, only hypoxic events were reported in Mediterranean Sea. The analysis of potential ecosystem vulnerability indicates that the ecosystems that are most sensitive to global change are deep-water coral systems and deep-sea plains. In addition, deep-sea canyons are also likely increasingly subjected to physical disturbance as a result of the increase in the frequency and intensity of climate-driven episodic events. Available information also suggests that biodiversity and ecosystem functioning of the deep Mediterranean Sea is undergoing dramatic changes, which result in accelerated organic matter biogeochemical cycling, miniaturization of the organisms’ size, increased metabolism, dominance of the microbial components, and mortality rates of deep-sea biota. Given the high sensitivity of the Mediterranean Sea to global change in comparison with other oceanic regions, and the vulnerability of its deep-sea habitats/ecosystems, specific policy measures are needed to protect its biodiversity, restore damaged habitats, and increase deep-sea ecosystems resistance and resilience to the ongoing impacts of global change.

Continue reading ‘Climate change impacts on the biota and on vulnerable habitats of the deep Mediterranean Sea’

Effects of ocean acidification on the levels of primary and secondary metabolites in the brown macroalga Sargassum vulgare at different time scales


Sargassum vulgare growing at CO2 vents was compared with those growing at control site.
S. vulgare from control site was transplanted to CO2 vents for 2 weeks.
• In short-term responses, S. vulgare showed increased level of sugars, PUFAs, and EAAs.
• Natural population at vents showed decreased sugars, PUFAs, phenols, and increased EAAs.
• Nutritional values of algae will decrease under acidification in long time scale.


Most of the studies regarding the impact of ocean acidification on macroalgae have been carried out for short-term periods, in controlled laboratory conditions, thus hampering the possibility to scale up the effects on long-term. In the present study, the volcanic CO2 vents off Ischia Island were used as a natural laboratory to investigate the metabolic response of the brown alga Sargassum vulgare to acidification at different time scales. For long-term effects, algal populations naturally growing at acidified and control sites were compared. For short-term responses, in situ reciprocal transplants from control to acidified site and vice-versa were performed. Changes in the levels of sugars, fatty acids (FAs), amino acids (AAs), antioxidants, and phenolic compounds were examined. Our main finding includes variable metabolic response of this alga at different time scales to natural acidification. The levels of sugars, FAs, and some secondary metabolites were lower in the natural population at the acidified site, whereas the majority of AAs were higher than those detected in thalli growing at control site. Moreover, in algae transplanted from control to acidified site, soluble sugars (glucose and mannose), majority of AAs, and FAs increased in comparison to control plants transplanted within the same site. The differences in the response of the macroalga suggest that the metabolic changes observed in transplants may be due to acclimation that supports algae to cope with acidification, thus leading to adaptation to lowered pH in long time scale.

Graphical abstract

Unlabelled Image

Continue reading ‘Effects of ocean acidification on the levels of primary and secondary metabolites in the brown macroalga Sargassum vulgare at different time scales’

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Ocean acidification in the IPCC AR5 WG II

OUP book