Posts Tagged 'Mediterranean'

Photosynthesis and mineralogy of Jania rubens at low pH/high pCO2: a future perspective


• Calcifying red algae may show species-specific response to ocean acidification (OA).
• Photosynthesis and mineralogy (biosphere) were assessed after a three-week transplant.
• Field carbon chemistry (hydrosphere) and irradiance (atmosphere) were also considered.
• Photosynthesis decreased while calcification was maintained under future pH conditions.
• The calcifying Jania rubens may survive but reducing the fitness under OA.


Corallinales (Rhodophyta) are high Mg-calcite macroalgae and are considered among the most vulnerable organisms to ocean acidification (OA). These sensitive species play fundamental roles in coastal systems as food source and settlement promoters as well as being involved in reef stabilization, and water carbonate balance. At present only a few studies are focused on erect calcifying macroalgae under low pH/high pCO2 and the contrasting results make difficult to predict the ecological consequences of the OA on the coralline algae. In this paper the physiological reasons behind the resistance of Jania rubens, one of the most common calcareous species, to changing ocean pH are analysed. In particular, we studied the photosynthetic and mineralogical response of J. rubens after a three-week transplant in a natural CO2 vent system. The overall results showed that J. rubens could be able to survive under predicted pH conditions even though with a reduced fitness; nevertheless physiological limits prevent the growth and survival of the species at pH 6.7. At low pH (i.e. pH 7.5), the maximum and effective PSII efficiency decreased even if the increase of Rubisco expression suggests a compensation effort of the species to cope with the decreased light-driven products. In these circumstances, a pH-driven bleaching phenomenon was also observed. Even though the photosynthesis decreased at low pH, J. rubens maintained unchanged the mineralogical composition and the carbonate content in the cell wall, suggesting that the calcification process may also have a physiological relevance in addition to a structural and/or a protective role. Further studies will confirm the hypotheses on the functional and evolutionary role of the calcification process in coralline algae and on the ecological consequences of the community composition changes under high pCO2 oceans.

Continue reading ‘Photosynthesis and mineralogy of Jania rubens at low pH/high pCO2: a future perspective’

CO2 leakage alters biogeochemical and ecological functions of submarine sands

Subseabed CO2 storage is considered a future climate change mitigation technology. We investigated the ecological consequences of CO2 leakage for a marine benthic ecosystem. For the first time with a multidisciplinary integrated study, we tested hypotheses derived from a meta-analysis of previous experimental and in situ high-CO2 impact studies. For this, we compared ecological functions of naturally CO2-vented seafloor off the Mediterranean island Panarea (Tyrrhenian Sea, Italy) to those of nonvented sands, with a focus on biogeochemical processes and microbial and faunal community composition. High CO2 fluxes (up to 4 to 7 mol CO2 m−2 hour−1) dissolved all sedimentary carbonate, and comigration of silicate and iron led to local increases of microphytobenthos productivity (+450%) and standing stocks (+300%). Despite the higher food availability, faunal biomass (−80%) and trophic diversity were substantially lower compared to those at the reference site. Bacterial communities were also structurally and functionally affected, most notably in the composition of heterotrophs and microbial sulfate reduction rates (−90%). The observed ecological effects of CO2 leakage on submarine sands were reproduced with medium-term transplant experiments. This study assesses indicators of environmental impact by CO2 leakage and finds that community compositions and important ecological functions are permanently altered under high CO2.

Continue reading ‘CO2 leakage alters biogeochemical and ecological functions of submarine sands’

Acidified seawater increases accumulation of cobalt but not cesium in manila clam Ruditapes philippinarum


• Co accumulation in clam Ruditapes philippinarum might double due to ocean acidification.
• The highest CF of cobalt was observed in acidified seawater (pH:7.5).
• The longest Tb1/2 of cobalt was seen in moderately acidified seawater (pH:7.8).
• Cs uptake in clam Ruditapes philippinarum is not affected by increased pCO2.


The pH of seawater around the world is expected to continue its decline in the near future in response to ocean acidification that is driven by heightened atmospheric CO2emissions. Concomitantly, economically-important molluscs that live in coastal waters including estuaries and embayments, may be exposed to a wide assortment of contaminants, including trace metals and radionuclides. Seawater acidification may alter both the chemical speciation of select elements as well as the physiology of organisms, and may thus pose at risk to many shellfish species, including the manila clam Ruditapes philippinarum. The bioconcentration efficiency of two common radionuclides associated with the nuclear fuel cycle, 134Cs and 57Co, were investigated by exposing live clams to dissolved 134Cs and 57Co at control (pH = 8.1) and two lowered pH (pH = 7.8 and 7.5) levels using controlled aquaria. The uptake and depuration kinetics of the two radionuclides in the whole-body clam were followed for 21 and 35 days, respectively. At steady-state equilibrium, the concentration factor (CFss) for 57Co increased as the pH decreased (i.e. 130 ± 5, 194 ± 6, and 258 ± 10 at pH levels 8.1, 7.8 and 7.5, respectively), whereas the 134Cs uptake was not influenced by a change in pH conditions. During depuration, the lowest depuration rate constant of 57Co by the manila clam was observed at the intermediate pH of 7.8. An increase in the accumulation of 57Co at the intermediate pH value was thought to be caused mainly by the aragonitic shell of the clam, as well as the low salinity and alkalinity of seawater used in the experiment. Considering that accumulation consists of uptake and depuration, among the three pH conditions moderately acidified seawater enhanced most the accumulation of 57Co. Accumulation of 134Cs was not strongly influenced by a reduced pH condition, as represented by an analogous uptake constant rate and CFss in each treatment. Such results suggest that future seawater pH values that are projected to be lower in the next decades, may pose a risk for calcium-bearing organisms such as shellfish.

Continue reading ‘Acidified seawater increases accumulation of cobalt but not cesium in manila clam Ruditapes philippinarum’

Expression of homing endonuclease gene and insertion-like element in sea anemone mitochondrial genomes: lesson learned from Anemonia viridis


• We report complete mitochondrial genome sequences and corresponding mito-transcriptomes of the two related sea anemone species Anemonia viridis and Anemonia majano
• We describe structural features of group I introns in the NADH dehydrogenase 5 gene and the cytochrome oxidase I (COI) gene, the latter containing a homing endonuclease gene
• We provide support of that the intron homing endonuclease gene is expressed in a gene-fusion strategy involving exon 1 of the COI gene
• We show that the insertion-like element orfA is well expressed from sea anemone mitochondrial geneomes
• Long-term environmental stress due to low-seawater pH conditions results in up-regulation of COI and orfA gene expressions in Anemonia viridis


The mitochondrial genomes of sea anemones are dynamic in structure. Invasion by genetic elements, such as self-catalytic group I introns or insertion-like sequences, contribute to sea anemone mitochondrial genome expansion and complexity. By using next generation sequencing we investigated the complete mtDNAs and corresponding transcriptomes of the temperate sea anemone Anemonia viridis and its closer tropical relative Anemonia majano. Two versions of fused homing endonuclease gene (HEG) organization were observed among the Actiniidae sea anemones; in-frame gene fusion and pseudo-gene fusion. We provided support for the pseudo-gene fusion organization in Anemonia species, resulting in a repressed HEG from the COI-884 group I intron. orfA, a putative protein-coding gene with insertion-like features, was present in both Anemonia species. Interestingly, orfA and COI expression were significantly up-regulated upon long-term environmental stress corresponding to low seawater pH conditions. This study provides new insights to the dynamics of sea anemone mitochondrial genome structure and function.

Continue reading ‘Expression of homing endonuclease gene and insertion-like element in sea anemone mitochondrial genomes: lesson learned from Anemonia viridis’

Elucidating the small regulatory RNA repertoire of the sea anemone Anemonia viridis based on whole genome and small RNA sequencing

Cnidarians harbor a variety of small regulatory RNAs that include microRNAs (miRNAs) and PIWI-interacting RNAs (piRNAs), but detailed information is limited. Here, we report the identification and expression of novel miRNAs and putative piRNAs, as well as their genomic loci, in the symbiotic sea anemone Anemonia viridis. We generated a draft assembly of the A. viridis genome with putative size of 313 Mb that appeared to be composed of about 36% repeats, including known transposable elements. We detected approximately equal fractions of DNA transposons and retrotransposons. Deep sequencing of small RNA libraries constructed from A. viridis adults sampled at a natural CO2 gradient off Vulcano Island, Italy, identified 70 distinct miRNAs. Eight were homologous to previously reported miRNAs in cnidarians, whereas 62 appeared novel. Nine miRNAs were recognized as differentially expressed along the natural seawater pH gradient. We found a highly abundant and diverse population of piRNAs, with a substantial fraction showing ping–pong signatures. We identified nearly 22% putative piRNAs potentially targeting transposable elements within the A. viridis genome. The A. viridis genome appeared similar in size to that of other hexacorals with a very high divergence of transposable elements resembling that of the sea anemone genus Exaiptasia. The genome encodes and expresses a high number of small regulatory RNAs, which include novel miRNAs and piRNAs. Differentially expressed small RNAs along the seawater pH gradient indicated regulatory gene responses to environmental stressors.

Continue reading ‘Elucidating the small regulatory RNA repertoire of the sea anemone Anemonia viridis based on whole genome and small RNA sequencing’

Limited carbonate dissolution by boring microflora at two volcanically acidified temperate sites: Ischia (Italy, Mediterranean Sea) and Faial (Azores, NE Atlantic Ocean)

In situ effects of ocean acidification on carbonate dissolution by microboring flora, also called biogenic dissolution, have only been studied once in tropical environments. Naturally acidified seawaters due to CO2 vents offer a perfect setting to study these effects in temperate systems. Three sites were selected at Ischia (Italy, Mediterranean Sea) with one experiencing ambient pH and the two others a mean pHT of 7.2 and 7.5. At Faial (Azores, NE Atlantic), one site with ambient pH and one acidified site with a mean pHT of 7.4 were selected. Experiments were carried out during 1.5 months and 6 months in Azores and Ischia, respectively, to determine the effects of OA on microboring communities in various carbonate substrates. Low pH influenced negatively boring microflora development by limiting their depth of penetration and abundance in substrates. Biogenic dissolution was thus reduced by a factor 3 to 7 depending on sites and substrate types. At sites with ambient pH in Faial, biogenic dissolution contributed up to 23% to the total weight loss, while it contributed less than 1% to the total weight loss of substrates at the acidified sites. Most of the dissolution at these sites was due to chemical dissolution (often Ω ≤ 1). Such conditions maintained microboring communities at a pioneer stage with a limited depth of penetration in substrates. Our results, together with previous findings which showed an increase of biogenic dissolution at pH >7.7, suggest that there is a pH tipping point below which microborer development and thus, carbonate biogenic dissolution, is strongly limited.

Continue reading ‘Limited carbonate dissolution by boring microflora at two volcanically acidified temperate sites: Ischia (Italy, Mediterranean Sea) and Faial (Azores, NE Atlantic Ocean)’

The distribution of benthic foraminifera in Bel Torrente submarine cave (Sardinia, Italy) and their environmental significance


• Benthic foraminifera in Mediterranean submarine caves were studied for the first time.
• Ecological zones were recognized in the cave environment.
• Change of environmental parameters influence species diversity and distribution.
• Species in the cave are not common in the Sardinian marine coastal area.
• An effective dispersal mechanism is supposed for cave colonization.


The use of benthic foraminifera as ecological indicators in submarine caves of temperate seas have never been studied before and it represents a new approach, verified by this research. The Bel Torrente submarine cave (Gulf of Orosei, Sardinia, Italy) was surveyed by GUE (Global Underwater Explorers) scuba divers in order to georeferencing the cave before positioning the sampling stations, from the entrance to 430 m inside the cave. A total of 15 water samples were collected to investigate abiotic parameters (temperature, salinity, pH) while 15 sediment samples were collected to analyze grain size and benthic foraminifera. Benthic foraminifera, investigated for the first time in a submarine cave of temperate areas, were exclusively found from the entrance to 300 m inside the cave. Species distribution and assemblage diversity have been found to be correlated to the environmental gradient towards the inner cave, mainly due to the decreasing of temperature and salinity and the increasing of the flow energy. Water acidification seems responsible for the transition from a calcareous hyaline-dominated assemblage to an agglutinant-dominated one, occurring between 120 and 150 m from the entrance. Common taxa of the Sardinian coastal marine area are present only close to the entrance of the cave, while species found in the inner part are nearly exclusively epifaunal clinging/attached or infaunal taxa, with tolerance for wide variability of environmental parameters, such as Gavelinopsis praegeri, and opportunist infaunal taxa such as Eggerella advena. The agglutinant taxa found in the cave are conversely very rare in coastal marine assemblages of the area. This suggests a very efficient dispersal mechanism for the colonization of the caves, involving probably juvenile foraminifera at a “propagule” stage.

Continue reading ‘The distribution of benthic foraminifera in Bel Torrente submarine cave (Sardinia, Italy) and their environmental significance’

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Ocean acidification in the IPCC AR5 WG II

OUP book