Posts Tagged 'Mediterranean'

Physiological and biochemical analyses shed light on the response of Sargassum vulgare to ocean acidification at different time scales

Studies regarding macroalgal responses to ocean acidification (OA) are mostly limited to short-term experiments in controlled conditions, which hamper the possibility to scale up the observations to long-term effects in the natural environment. To gain a broader perspective, we utilized volcanic CO2 vents as a “natural laboratory” to study OA effects on Sargassum vulgare at different time scales. We measured photosynthetic rates, oxidative stress levels, antioxidant contents, antioxidant enzyme activities, and activities of oxidative metabolic enzymes in S. vulgare growing at a natural acidified site (pH 6.7) compared to samples from a site with current pH (pH 8.2), used as a control one. These variables were also tested in plants transplanted from the control to the acidified site and vice-versa. After short-term exposure, photosynthetic rates and energy metabolism were increased in S. vulgare together with oxidative damage. However, in natural populations under long-term conditions photosynthetic rates were similar, the activity of oxidative metabolic enzymes was maintained, and no sign of oxidative damages was observed. The differences in the response of the macroalga indicate that the natural population at the acidified site is adapted to live at the lowered pH. The results suggest that this macroalga can adopt biochemical and physiological strategies to grow in future acidified oceans.

Continue reading ‘Physiological and biochemical analyses shed light on the response of Sargassum vulgare to ocean acidification at different time scales’

Coastal ocean acidification and increasing total alkalinity in the northwestern Mediterranean Sea

Coastal time series of ocean carbonate chemistry are critical for understanding how global anthropogenic change manifests in near-shore ecosystems. Yet, they are few and have low temporal resolution. At the time series station Point B in the northwestern Mediterranean Sea, seawater was sampled weekly from 2007 through 2015, at 1 and 50 m, and analyzed for total dissolved inorganic carbon (CT) and total alkalinity (AT). Parameters of the carbonate system such as pH (pHT, total hydrogen ion scale) were calculated and a deconvolution analysis was performed to identify drivers of change. The rate of surface ocean acidification was −0.0028 ± 0.0003 units pHT yr−1. This rate is larger than previously identified open-ocean trends due to rapid warming that occurred over the study period (0.072 ± 0.022 °C yr−1). The total pHT change over the study period was of similar magnitude as the diel pHT variability at this site. The acidification trend can be attributed to atmospheric carbon dioxide (CO2) forcing (59 %, 2.08 ± 0.01 ppm CO2 yr−1) and warming (41 %). Similar trends were observed at 50 m but rates were generally slower. At 1 m depth, the increase in atmospheric CO2 accounted for approximately 40 % of the observed increase in CT (2.97 ± 0.20 µmol kg−1 yr−1). The remaining increase in CT may have been driven by the same unidentified process that caused an increase in AT (2.08 ± 0.19 µmol kg−1 yr−1). Based on the analysis of monthly trends, synchronous increases in CT and AT were fastest in the spring–summer transition. The driving process of the interannual increase in AT has a seasonal and shallow component, which may indicate riverine or groundwater influence. This study exemplifies the importance of understanding changes in coastal carbonate chemistry through the lens of biogeochemical cycling at the land–sea interface. This is the first coastal acidification time series providing multiyear data at high temporal resolution. The data confirm rapid warming in the Mediterranean Sea and demonstrate coastal acidification with a synchronous increase in total alkalinity.

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Low planktic foraminiferal diversity and abundance observed in a spring 2013 west–east Mediterranean Sea plankton tow transect (update)

Planktic foraminifera were collected with 150 µm BONGO nets from the upper 200 m water depth at 20 stations across the Mediterranean Sea between 2 May and 2 June 2013. The main aim is to characterize the species distribution and test the covariance between foraminiferal area density (ρA) and seawater carbonate chemistry in a biogeochemical gradient including ultraoligotrophic conditions. Average foraminifera abundances are 1.42 ± 1.43 ind. 10 m−3 (ranging from 0.11 to 5.20 ind. 10 m−3), including 12 morphospecies. Large differences in species assemblages and total abundances are observed between the different Mediterranean sub-basins, with an overall dominance of spinose, symbiont-bearing species indicating oligotrophic conditions. The highest values in absolute abundance are found in the Strait of Gibraltar and the Alboran Sea. The western basin is dominated by Globorotalia inflata and Globigerina bulloides at slightly lower standing stocks than in the eastern basin. In contrast, the planktic foraminiferal assemblage in the warmer, saltier, and more nutrient-limited eastern basin is dominated by Globigerinoides ruber (white). These new results, when combined with previous findings, suggest that temperature-induced surface water stratification and food availability are the main factors controlling foraminiferal distribution. In the oligotrophic and highly alkaline and supersaturated with respect to calcite and aragonite Mediterranean surface water, standing stocks and ρA of G. ruber (white) and G. bulloides are affected by both food availability and seawater carbonate chemistry. Rapid warming increased surface ocean stratification impacting food availability and changes in trophic conditions could be the causes of reduced foraminiferal abundance, diversity, and species-specific changes in planktic foraminiferal calcification.

Continue reading ‘Low planktic foraminiferal diversity and abundance observed in a spring 2013 west–east Mediterranean Sea plankton tow transect (update)’

Structural and functional organization of fish assemblages in a Mediterranean shallow CO2 vent

The “business-as-usual emission scenario” simulated by the IPCC (Intergovernmental Panel on Climate Change) suggests that atmospheric CO2 levels could approach 800 ppm by the end of the century. Corresponding biogeochemical models indicate that surface ocean water pH will drop from a pre-industrial value of about 8.2 to 7.8 within 2100 (Feely et al., 2010). This phenomenon known as “Ocean Acidification” (OA) is caused by the increasing CO2 emissions due to anthropic activities, with a current consequence decrease of about 0.1 unit of pH (Caldeira & Wickett 2003) that is having effects on seawater carbonate chemistry and on marine ecosystems. Many short-term laboratory experiments have shown the effects of OA on marine calcareous organisms (Doney et al., 2009), but also on not-calcifying ones. For instance, experiments on fish have revealed effects on physiological and behavioral aspects (Dixson et al., 2010; Munday et al., 2009), but many other aspects are still unknown (Ishimatsu et al., 2008). On the other hand, field experiments have been conducted in naturally acidified marine ecosystems, known as CO2 vents, which are currently investigated to study the long-term effects of OA on species, communities and ecological processes (Hall-Spencer et al. 2008).

Shallow CO₂ vents are widespread in Mediterranean (Dando et al., 1999) and represent a sort of natural mesocosms, where marked pH gradients are present at small spatial scales. The aim of this PhD project is to assess the effect of high pCO2/low pH on the structural and functional organization of fish assemblages in a Mediterranean shallow CO₂ vent (Aeolian Archipelago, NE Sicily). In particular, we compare the responses of a chronic exposed fish assemblage living near the primary vent (mean pH = 7.8; hereafter “Low pH”) with other two fish assemblages living at normal pH (mean pH = 8.2; hereafter “Control 1” and “Control 2”) in Vulcano and Lipari Islands. We hypothesized that the organization of fish assemblage at the low pH site is different from that in controls. To test our hypothesis we use several descriptors and different methodologies. First, we compared fish community structure by using Underwater Visual Census technique to assess species richness and abundance (frequency of occurrence). Then we carried out samplings to evaluate trophic organization of fish assemblages (we used stable isotopes of carbon and nitrogen to analyze food web and trophic levels), bioaccumulation and biomagnification of trace elements (concentration and bio-availability of several trace elements, also toxic ones, may increase due to direct input from the vent and to peculiar pH and Eh conditions), and the characteristics of carbonate structures like otoliths (to assess the effect of acidification on these structures by morphological analysis). Otoliths are also used as natural tags to study fish “site fidelity” of this particular site through microchemistry analysis of trace elements and isotopic composition.

This study provided a complete and exhaustive frame of fish assemblages structure and trophic organization at different pH levels. As scant data are available in the literature on this topic, the results of this research provide information about the ecological effects of long-term exposure to high CO2 levels on fish, a key biological component whose monitoring is relevant not only from the ecological side, but also for the economic one and for the implications on human health. Moreover, this study confirms the importance to use the naturally acidified environments to test ecological hypotheses on the effects of OA on communities and ecosystems.

Continue reading ‘Structural and functional organization of fish assemblages in a Mediterranean shallow CO2 vent’

Inorganic carbon physiology underpins macroalgal responses to elevated CO2

Beneficial effects of CO2 on photosynthetic organisms will be a key driver of ecosystem change under ocean acidification. Predicting the responses of macroalgal species to ocean acidification is complex, but we demonstrate that the response of assemblages to elevated CO2 are correlated with inorganic carbon physiology. We assessed abundance patterns and a proxy for CO2:HCO3− use (δ13C values) of macroalgae along a gradient of CO2 at a volcanic seep, and examined how shifts in species abundance at other Mediterranean seeps are related to macroalgal inorganic carbon physiology. Five macroalgal species capable of using both HCO3− and CO2 had greater CO2 use as concentrations increased. These species (and one unable to use HCO3−) increased in abundance with elevated CO2 whereas obligate calcifying species, and non-calcareous macroalgae whose CO2 use did not increase consistently with concentration, declined in abundance. Physiological groupings provide a mechanistic understanding that will aid us in determining which species will benefit from ocean acidification and why.

Continue reading ‘Inorganic carbon physiology underpins macroalgal responses to elevated CO2’

Carbonate system parameters and anthropogenic CO2 in the North Aegean Sea in October 2013

Data of AT (total alkalinity) and CT (total inorganic carbon) collected during October 2013, on a N-S transect crossing the North of Lemnos basin allowed to identify the peculiarities of the CO2 system in the North Aegean Sea and estimate the anthropogenic CO2 (CANT) concentrations.

Extremely high concentrations of AT and CT were recorded in the upper layer of the North Aegean reflecting the high loads of AT and CT by the brackish BSW (Black Sea Water) outflowing through the Dardanelles strait and by the local rivers runoff. Both AT and CTexhibit strong negative linear correlation with salinity in the upper layer (0–20 m). Investigation of the AT-S relationship along with the salinity adjustment of AT revealed excess alkalinity throughout the water column in relation to surface waters implying the possible occurrence of non-carbonate alkalinity inputs and of other processes taking place probably over the extended shelves that contribute to the alkalinity surplus.

The intermediate layer occupied by the Modified Levantine Intermediate Water (MLIW) mass exhibits the lowest CT and AT concentrations, while rather elevated AT and CTconcentrations characterize the North Aegean Deep Water (NAgDW) mass filling the deep layer of the North of Lemnos basin linked to previous dense water formation episodes.

High anthropogenic CO2 content was detected at intermediate and deep layers of the North Aegean reflecting the effective transportation of the absorbed atmospheric CO2 at the surface to the deeper waters via the dense water formation episodes. The MLIW layer is more affected by the penetration of CANT than the NAgDW that fills the deep part of the basin. The observed variability of CANT distribution reflects the influence of the intensity of dense water formation events, of the different θ/S properties of the newly formed dense waters as well as of the diverse submarine pathways followed by the cascading dense waters. The invasion of CANT has lead to more acidic conditions and to lower saturation degree of calcium carbonate in relation to the preindustrial era. The findings of this study provide baseline information about the carbonate system properties of the North Aegean and highlight its active role in sequestering and storing anthropogenic CO2.

Continue reading ‘Carbonate system parameters and anthropogenic CO2 in the North Aegean Sea in October 2013’

Anthropogenic CO2 in a dense water formation area of the Mediterranean Sea

There is growing evidence that the on-going ocean acidification of the Mediterranean Sea could be favoured by its active overturning circulation. The areas of dense water formation are, indeed, preferential sites for atmospheric carbon dioxide absorption and through them the ocean acidification process can quickly propagate into the deep layers.

In this study we estimated the concentration of anthropogenic CO2 (Cant) in the dense water formation areas of the middle and southern Adriatic Sea. Using the composite tracer TrOCA (Tracer combining Oxygen, inorganic Carbon, and total Alkalinity) and carbonate chemistry data collected throughout March 2013, our results revealed that a massive amount of Cant has invaded all the identified water masses. High Cantconcentration was detected at the bottom layer of the Pomo Pit (middle Adriatic, 96.8 ± 9.7 µmol kg−1) and Southern Adriatic Pit (SAP, 85.2 ± 9.4 µmol kg−1), associated respectively with the presence of North Adriatic Dense Water (NAdDW) and Adriatic Dense Water (AdDW). This anthropogenic contamination was clearly linked to the dense water formation events, which govern strong CO2 flux from the atmosphere to the sea and the sinking of dense, CO2-rich surface waters to the deep sea. However, a very high Cant level (94.5 ± 12.5 µmol kg−1) was also estimated at the intermediate layer, as a consequence of a recent vertical mixing that determined the physical and biogeochemical modification of the water of Levantine origin (i.e. Modified Levantine Intermediate Water, MLIW) and favoured the atmospheric CO2 intrusion.

The penetration of Cant in the Adriatic Sea determined a significant pH reduction since the pre-industrial era (– 0.139 ± 0.019 pH units on average). This estimation was very similar to the global Mediterranean Sea acidification, but it was again more pronounced at the bottom of the Pomo Pit, within the layer occupied by NAdDW (– 0.157 ± 0.019 pH units), and at the intermediate layer of the recently formed MLIW (– 0.143 ± 0.019 pH units). Our results indicate that the Adriatic Sea could potentially be one of the Mediterranean regions most affected by the ocean acidification and also demonstrate its active role in sequestering and storing Cant.

Continue reading ‘Anthropogenic CO2 in a dense water formation area of the Mediterranean Sea’


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Ocean acidification in the IPCC AR5 WG II

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