Posts Tagged 'Mediterranean'

Temporal and spatial variability of the CO2 system in a riverine influenced area of the Mediterranean Sea, the Northern Adriatic

Coastal ecosystems are subject to multiple processes that drive pH change over time. Therefore, efforts to understand the variability in the coastal carbonate system are crucial to assess the marine system vulnerability to acidification. The variations of the carbon dioxide (CO2) system were studied, from December 2014 to January 2017, on 6 stations along a transect latitudinally crossing the northern Adriatic, from the Po River delta to the Istrian Peninsula. The study aims to evaluate the influence of riverine inputs and other environmental drivers, such as temperature, air-sea CO2 exchanges and biological processes, on the carbonate system. Riverine discharges significantly affected the carbonate system, as they are an input of total alkalinity and nutrients. High alkalinity concentrations were measured in low salinity waters and a significant negative correlation between salinity and alkalinity was found. The influence of biological processes was underscored by the significant inverse correlation between pHT at a constant temperature (pHT25^°C) and apparent oxygen utilization, and by the positive correlation between chlorophyll a and pHT25^°C in samplings close to flood events. Moreover, thermic and non-thermic partial pressure (p) of CO2 in surface waters was evaluated. pCO2 was more strongly influenced by the thermal effect during summer, while the biological effect prevailed in the other seasons. The analysis of air-sea CO2 fluxes highlighted that the area acts as a sink of CO2 during winter, spring and autumn and as a source during summer. A biogeochemical simulation was used for bottom and surface waters to estimate future changes in northern Adriatic carbonate chemistry with the increase of anthropogenic CO2 and temperature, and to understand how biological processes could affect the expected trends. By 2100, under the IPCC scenario of business as usual and without the effect of biological processes, pHT is expected to decrease by ∼0.3 and the aragonite saturation is expected to decline by ∼1.3, yet not reach undersaturation values. Even though the northern Adriatic is characterized by high alkalinity buffering, pH seasonal variability will likely be more pronounced, due to the strong decoupling of production and respiration processes driven by stratification of the water column.

Continue reading ‘Temporal and spatial variability of the CO2 system in a riverine influenced area of the Mediterranean Sea, the Northern Adriatic’

A regional neural network approach to estimate water-column nutrient concentrations and carbonate system variables in the Mediterranean Sea: CANYON-MED

A regional neural network-based method, “CANYON-MED” is developed to estimate nutrients and carbonate system variables specifically in the Mediterranean Sea over the water column from pressure, temperature, salinity, and oxygen together with geolocation and date of sampling. Six neural network ensembles were developed, one for each variable (i.e., three macronutrients: nitrates (NO−33-), phosphates (PO3−443-) and silicates (SiOH4), and three carbonate system variables: pH on the total scale (pHT), total alkalinity (AT), and dissolved inorganic carbon or total carbon (CT), trained using a specific quality-controlled dataset of reference “bottle” data in the Mediterranean Sea. This dataset is representative of the peculiar conditions of this semi-enclosed sea, as opposed to the global ocean. For each variable, the neural networks were trained on 80% of the data chosen randomly and validated using the remaining 20%. CANYON-MED retrieved the variables with good accuracies (Root Mean Squared Error): 0.73 μmol.kg–1 for NO−33-, 0.045 μmol.kg–1 for PO3−443- and 0.70 μmol.kg–1 for Si(OH)4, 0.016 units for pHT, 11 μmol.kg–1 for AT and 10 μmol.kg–1 for CT. A second validation on the ANTARES independent time series confirmed the method’s applicability in the Mediterranean Sea. After comparison to other existing methods to estimate nutrients and carbonate system variables, CANYON-MED stood out as the most robust, using the aforementioned inputs. The application of CANYON-MED on the Mediterranean Sea data from autonomous observing systems (integrated network of Biogeochemical-Argo floats, Eulerian moorings and ocean gliders measuring hydrological properties together with oxygen concentration) could have a wide range of applications. These include data quality control or filling gaps in time series, as well as biogeochemical data assimilation and/or the initialization and validation of regional biogeochemical models still lacking crucial reference data. Matlab and R code are available at https:// github.com/MarineFou/CANYON-MED/.

Continue reading ‘A regional neural network approach to estimate water-column nutrient concentrations and carbonate system variables in the Mediterranean Sea: CANYON-MED’

Behavioural responses to predators in Mediterranean mussels (Mytilus galloprovincialis) are unaffected by elevated pCO2

Highlights

  • Tested effects of elevated CO2 on valve gaping responses to predator alarm cues in Mediterranean mussels.
  • Mussels reduced valve gaping in response to predator alarm cues; no change in valve movement activity.
  • Elevated CO2 had no effect on baseline behaviour nor responses to predator cues.
  • Behavioural responses to predator cues in bivalves appear robust to high CO2.

Abstract

Ocean acidification is expected to affect marine organisms in the near future. Furthermore, abrupt short-term fluctuations in seawater pCO2 characteristic of near-short coastal regions and high-density aquaculture sites currently have the potential to influence organismal and community functioning by altering animal behaviour. While anti-predator responses in fishes exposed to elevated pCO2 are well documented, such responses in benthic marine invertebrates are poorly studied. We used high frequency, non-invasive biosensors to test whether or not short term (3-week) exposure to elevated pCO2 could impact behavioural responses to the threat of predation in adult Mediterranean mussels from Galicia on the northwestern coast of Spain. Predator alarm cues (crushed conspecifics) resulted in a prolonged (1 h) reduction in the degree of valve opening (−20%) but had no clear effect on overall valve movement activity, while elevated pCO2 did not affect either response. Our results add to the increasing body of evidence suggesting that the effects of end-of-century pCO2 levels on marine animal behaviour are likely weak. Nonetheless, longer-term exposures spanning multiple generations are needed to better understand how ocean acidification might impact behavioural responses to predation in marine bivalves.

Continue reading ‘Behavioural responses to predators in Mediterranean mussels (Mytilus galloprovincialis) are unaffected by elevated pCO2’

Impact of dust enrichment on Mediterranean plankton communities under present and future conditions of pH and temperature: an experimental overview

In Low Nutrient Low Chlorophyll areas, such as the Mediterranean Sea, atmospheric fluxes represent a considerable external source of nutrients likely supporting primary production especially during stratification periods. These areas are expected to expand in the future due to lower nutrient supply from sub-surface waters caused by enhanced stratification, likely further increasing the role of atmospheric deposition as a source of new nutrients to surface waters. Yet, whether plankton communities will react differently to dust deposition in a warmer and acidified environment remains an open question. The impact of dust deposition both in present and future climate conditions was assessed through three perturbation experiments in the open Mediterranean Sea. Climate reactors (300 L) were filled with surface water collected in the Tyrrhenian Sea, Ionian Sea and in the Algerian basin during a cruise conducted in May/June 2017 in the frame of the PEACETIME project. The experimental protocol comprised two unmodified control tanks, two tanks enriched with a Saharan dust analog and two tanks enriched with the dust analog and maintained under warmer (+3 °C) and acidified (−0.3 pH unit) conditions. Samples for the analysis of an extensive number of biogeochemical parameters and processes were taken over the duration of the experiments (3–4 d). Here, we present the general setup of the experiments and the impacts of dust seeding and/or future climate change scenario on nutrients and biological stocks. Dust addition led to a rapid and maximum input of nitrate whereas phosphate release from the dust analog was much smaller. Our results showed that the impacts of Saharan dust deposition in three different basins of the open Northwestern Mediterranean Sea are at least as strong as those observed previously in coastal waters. However, interestingly, the effects of dust deposition on biological stocks were highly different between the three investigated stations and could not be attributed to differences in their degree of oligotrophy but rather to the initial metabolic state of the community. Finally, ocean acidification and warming did not drastically modify the composition of the autotrophic assemblage with all groups positively impacted by warming and acidification, suggesting an exacerbation of effects from atmospheric dust deposition in the future.

Continue reading ‘Impact of dust enrichment on Mediterranean plankton communities under present and future conditions of pH and temperature: an experimental overview’

Effects of salinity and pH of seawater on the reproduction of the sea urchin Paracentrotus lividus

Fertilization and early development are usually the most vulnerable stages in the life of marine animals, and the biological processes during this period are highly sensitive to the environment. In nature, sea urchin gametes are shed in seawater, where they undergo external fertilization and embryonic development. In a laboratory, it is possible to follow the exact morphological and biochemical changes taking place in the fertilized eggs and the developing embryos. Thus, observation of successful fertilization and the subsequent embryonic development of sea urchin eggs can be used as a convenient biosensor to assess the quality of the marine environment. In this paper, we have examined how salinity and pH changes affect the normal fertilization process and the following development of Paracentrotus lividus. The results of our studies using confocal microscopy, scanning and transmission electron microscopy, and time-lapse Ca2+ image recording indicated that both dilution and acidification of seawater have subtle but detrimental effects on many aspects of the fertilization process. They include Ca2+ signaling and coordinated actin cytoskeletal changes, leading to a significantly reduced rate of successful fertilization and, eventually, to abnormal or delayed embryonic development.

Continue reading ‘Effects of salinity and pH of seawater on the reproduction of the sea urchin Paracentrotus lividus’

Coccolithophore community response to ocean acidification and warming in the Eastern Mediterranean Sea: results from a mesocosm experiment

Mesocosm experiments have been fundamental to investigate the effects of elevated CO2 and ocean acidification (OA) on planktic communities. However, few of these experiments have been conducted using naturally nutrient-limited waters and/or considering the combined effects of OA and ocean warming (OW). Coccolithophores are a group of calcifying phytoplankton that can reach high abundances in the Mediterranean Sea, and whose responses to OA are modulated by temperature and nutrients. We present the results of the first land-based mesocosm experiment testing the effects of combined OA and OW on an oligotrophic Eastern Mediterranean coccolithophore community. Coccolithophore cell abundance drastically decreased under OW and combined OA and OW (greenhouse, GH) conditions. Emiliania huxleyi calcite mass decreased consistently only in the GH treatment; moreover, anomalous calcifications (i.e. coccolith malformations) were particularly common in the perturbed treatments, especially under OA. Overall, these data suggest that the projected increase in sea surface temperatures, including marine heatwaves, will cause rapid changes in Eastern Mediterranean coccolithophore communities, and that these effects will be exacerbated by OA.

Continue reading ‘Coccolithophore community response to ocean acidification and warming in the Eastern Mediterranean Sea: results from a mesocosm experiment’

Epiphytes provide micro-scale refuge from ocean acidification

Highlights

• OA induced bleaching and reduced metabolism in non-epiphytized coralline.

• Epiphytized corallines were less susceptible to the detrimental effects of OA.

• Epiphytized corallines had thicker diffusive boundary layer than non-epiphytized.

• Non-calcifying epiphytes provide small scale refuge from OA.

• Epiphytic refugia may protect corallines under future OA conditions.

Abstract

Coralline algae, a major calcifying component of coastal shallow water communities, have been shown to be one of the more vulnerable taxonomic groups to ocean acidification (OA). Under OA, the interaction between corallines and epiphytes was previously described as both positive and negative. We hypothesized that the photosynthetic activity and the complex structure of non-calcifying epiphytic algae that grow on corallines ameliorate the chemical microenvironmental conditions around them, providing protection from OA. Using mesocosm and microsensor experiments, we showed that the widespread coralline Ellisolandia elongata is less susceptible to the detrimental effects of OA when covered with non-calcifying epiphytic algae, and its diffusive boundary layer is thicker than when not covered by epiphytes. By modifying the microenvironmental carbonate chemistry, epiphytes, facilitated by OA, create micro-scale shield (and refuge) with more basic conditions that may allow the persistence of corallines associated with them during acidified conditions. Such ecological refugia could also assist corallines under near-future anthropogenic OA conditions.

Continue reading ‘Epiphytes provide micro-scale refuge from ocean acidification’

Long-term effects of elevated CO2 on the population dynamics of the seagrass Cymodocea Nodosa: evidence from volcanic seeps

We used population reconstruction techniques to assess for the first time the population dynamics of a seagrass, Cymodocea nodosa, exposed to long-term elevated CO2 near three volcanic seeps and compare them with reference sites away from the seeps. Under high CO2, the density of shoots and of individuals (apical shoots), and the vertical and horizontal elongation and production rates, were higher. Nitrogen effects on rhizome elongation and production rates and on biomass, were stronger than CO2 as these were highest at the location where the availability of nitrogen was highest. At the seep where the availability of CO2 was highest and nitrogen lowest, density of shoots and individuals were highest, probably due to CO2 effects on shoot differentiation and induced reproductive output, respectively. In all three seeps there was higher short- and long-term recruitment and growth rates around zero, indicating that elevated CO2 increases the turnover of C. nodosa shoots.

Continue reading ‘Long-term effects of elevated CO2 on the population dynamics of the seagrass Cymodocea Nodosa: evidence from volcanic seeps’

Ocean acidification alters the responses of invertebrates to wound-activated infochemicals produced by epiphytes of the seagrass Posidonia oceanica

Highlights

• First time evaluation of the effect of infochemicals produced at two pH by the epiphytic community and by selected diatoms.

• O.A. alters the fine-tuned chemical cross-talks between seagrass epiphytes and associated invertebrates.

• Algae play their roles at different concentrations and convey different messages to associated animal communities.

• O.A. has consequences on the structure of associated communities and food webs of seagrass ecosystems.

Abstract

Ocean acidification (OA) influences the production of volatile organic compounds (VOCs) by seagrass leaves and their associated epiphytes. We hypothesize that the perception of “odour” produced by seagrass leaf epiphytes will change with seawater acidification, affecting the behaviour of seagrass-associated invertebrates. To test this hypothesis, we collected epiphytes from leaves of Posidonia oceanica growing at two pH conditions (7.7 and 8.1) and identified the most abundant genera of diatoms. We tested the VOCs produced at pH 8.1 by the epiphytic communities in toto, as well as those produced by selected diatoms, on various invertebrates. A complex set of species-specific and concentration-dependent chemotactic reactions was recorded, according to the pH of seawater. In particular, VOCs produced by individual diatoms triggered contrasting reactions in invertebrates, depending on the pH. The perception of epiphyte VOCs is likely to vary due to alteration of species ability to perceive and/or interpret chemical cues as infochemicals or due to changes in the structure of VOCs themselves. Thus, OA alters the fine-tuned chemical cross-talks between seagrass epiphytes and associated invertebrates, with potential consequences for the structure of communities and food webs of seagrass ecosystems.

Continue reading ‘Ocean acidification alters the responses of invertebrates to wound-activated infochemicals produced by epiphytes of the seagrass Posidonia oceanica’

Do males and females respond differently to ocean acidification? an experimental study with the sea urchin Paracentrotus lividus

Seawater pH lowering, known as ocean acidification, is considered among the major threats to marine environment. In this study, post-spawning adults of the sea urchin Paracentrotus lividus were maintained at three pH values (8.0, 7.7, 7.4) for 60 days. Physiological, biochemical, cellular, behavioural and reproductive responses were evaluated in males and females. Significant differences between sexes were observed, with higher ammonia excretion and lower catalase activity in males. Respiration rate (after 21 days), catalase activity in gonads and total coelomocyte count showed the same increasing trend in males and females under low pH. Ammonia excretion, gonadosomatic index and lysozyme activity exhibited opposite responses to low pH, with an increasing trend in males and decreasing in females. Results demonstrated that exposure to low pH could result in different response strategies of male and female sea urchins at a physiological, biochemical and immunological level. Reduced female gonadosomatic index under low pH suggested decreased energy investment in reproduction.

Continue reading ‘Do males and females respond differently to ocean acidification? an experimental study with the sea urchin Paracentrotus lividus’


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Ocean acidification in the IPCC AR5 WG II

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