Posts Tagged 'Mediterranean'

Reproduction of an azooxanthellate coral is unaffected by ocean acidification

Anthropogenic carbon dioxide (CO2) emissions and consequent ocean acidification (OA) are projected to have extensive consequences on marine calcifying organisms, including corals. While the effects of OA on coral calcification are well documented, the response of reproduction is still poorly understood since no information are reported for temperate corals. Here we investigate for the first time the influence of OA on sexual reproduction of the temperate azooxanthellate solitary scleractinian Leptopsammia pruvoti transplanted along a natural pCO2 gradient at a Mediterranean CO2 vent. After 3 months, future projection of pH levels did not influence the germ cell production, gametogenesis and embryogenesis in this azooxanthellate coral. These findings suggest that reproductive potential may be quite tolerant to decreasing pH, with implications for ecosystem function and services in a changing ocean.

Continue reading ‘Reproduction of an azooxanthellate coral is unaffected by ocean acidification’

Target gene expression studies on Platynereis dumerilii and Platynereis cfr massiliensis at the shallow CO2 vents off Ischia, Italy

Many studies predict negative effects of ocean acidification on marine organisms, potentially leading to loss of biodiversity and ecosystem function. Research on species inhabiting naturally high pCO2 environments, such as volcanic CO2 vents, offers an opportunity to understand the molecular mechanisms involved in high pCO2 regulation. Here we investigate the relative expression of NADH dehydrogenase, sodium-hydrogen antiporter (NHE), carbonic anhydrase (CA) and paramyosin genes from two non-calcifying sibling Nereididae polychaetes species, Platynereis cfr massiliensis, collected in the shallow CO2 vents off Ischia (Italy; 40°43′52.0″N 13°57′46.2″E and 40°43′55.5″N 13°57′48.4″E), and P. dumerilii collected in an area nearby (40°43′34.51″N; 13°57′35.7″E). The origin of the worms was confirmed using restriction enzyme digest. NHE and paramyosin expressions were both significantly increased in P. dumerilii relative to the P. cfr massiliensis vent populations. Furthermore, a seven day laboratory transfer experiment to lower/higher pCO2 conditions was conducted to investigate the effects on the short term gene expression. The transfer experiment of the non-vent worms to high pCO2 conditions showed no significant effect on any of the genes analysed, however, two genes (NADH dehydrogenase and NHE) from worms of the vent population were significantly down-regulated under low pCO2. These findings will help to gain further insights into the cellular mechanisms affected by pCO2 changes in two polychaete species.

Continue reading ‘Target gene expression studies on Platynereis dumerilii and Platynereis cfr massiliensis at the shallow CO2 vents off Ischia, Italy’

Nutrient loading fosters seagrass productivity under ocean acidification

The effects of climate change are likely to be dependent on local settings. Nonetheless, the compounded effects of global and regional stressors remain poorly understood. Here, we used CO2 vents to assess how the effects of ocean acidification on the seagrass, Posidonia oceanica, and the associated epiphytic community can be modified by enhanced nutrient loading. P. oceanica at ambient and low pH sites was exposed to three nutrient levels for 16 months. The response of P. oceanica to experimental conditions was assessed by combining analyses of gene expression, plant growth, photosynthetic pigments and epiphyte loading. At low pH, nutrient addition fostered plant growth and the synthesis of photosynthetic pigments. Overexpression of nitrogen transporter genes following nutrient additions at low pH suggests enhanced nutrient uptake by the plant. In addition, enhanced nutrient levels reduced the expression of selected antioxidant genes in plants exposed to low pH and increased epiphyte cover at both ambient and low pH. Our results show that the effects of ocean acidification on P. oceanica depend upon local nutrient concentration. More generally, our findings suggest that taking into account local environmental settings will be crucial to advance our understanding of the effects of global stressors on marine systems.

Continue reading ‘Nutrient loading fosters seagrass productivity under ocean acidification’

Hydrological conditions and phytoplankton community in the Lesina lagoon (southern Adriatic Sea, Mediterranean)

The Lesina lagoon (southern Adriatic Sea, Mediterranean) is a coastal lagoon located in a highly intensified farming and tourist area. A monthly sampling was carried out in 1998 in five stations, representative of different hydrological features, in order to analyse phytoplankton composition and its relation to environmental parameters. Our results showed high spatial variability of abiotic variables. Phytoplankton abundances and biomass trends showed marked seasonality, with annual peaks occurring in late winter–early spring and summer periods. Phytoplankton blooms were due to the diatom Thalassiosira pseudonana and the dinoflagellate Prorocentrum cordatum. Statistical analyses showed that salinity and nutrients were the main factors affecting phytoplankton abundance and biomass. Phytoplankton dynamics was associated both to seasonality and the hydrodynamic regime of the system. Moreover, chemical–physical data were analysed together with those collected in the same stations in 2007, to compare their dynamics under different hydrological regimes. The two periods corresponded to the closure and opening, respectively, of canals connecting the lagoon to the sea. In general, abiotic variables (salinity, dissolved oxygen, pH, nitrate, phosphate and silicate concentrations) were significantly affected by the hydrodynamic regime. These data could provide a useful basis to complement the knowledge gained through current monitoring within the framework of the European Directives, as well as to implement conservation and management strategies of these transitional waters.

Continue reading ‘Hydrological conditions and phytoplankton community in the Lesina lagoon (southern Adriatic Sea, Mediterranean)’

Ocean acidification does not impair predator recognition but increases juvenile growth in a temperate wrasse off CO2 seeps

Highlights

  • CO2 effects on the ocellated wrasse predator cue recognition were assessed.
  • Behavioural and otolith analyses were performed on Symphodus ocellatus from CO2 seeps.
  • Predation risk perception by the ocellated wrasse juveniles was unaffected by CO2.
  • High CO2 levels enhanced the S. ocellatus post-settlement growth.

Abstract

Fish behavioural effects under Ocean Acidification (OA) rely on changes expected to occur in brain function, which can be reversed by gabazine, a GABA-A antagonist. Here, using standard two-channel choice flume, we assessed OA effects on the predator recognition ability of both gabazine-treated and -untreated Symphodus ocellatus post-settlers living off CO2 seeps in the Mediterranean Sea. To estimate the post-settlers background predation risk we evaluated the density of their predator in the wild and through otolith aging techniques we assessed their post-settlement growth. Results showed that: 1) post-settlers predator recognition was unaffected under OA; 2) post-settlers living in elevated CO2 were on average 15% bigger in size than those from ambient conditions. Our results support fish behavioural tolerance to OA, potentially mediated by pre-exposure to high-risk predation levels, and speculate that by increasing body size, juvenile fish might more efficiently avoid their predators.
Continue reading ‘Ocean acidification does not impair predator recognition but increases juvenile growth in a temperate wrasse off CO2 seeps’

Atmospheric nutrients in seawater under current and high pCO2 conditions after Saharan dust deposition: results from three minicosm experiments

Highlights

  • Ocean acidification will not alter the input of new nitrogen from dust in surface waters.
  • Transient increase in dissolved iron and phosphate concentrations was driven by adsorption and aggregation processes, regardless of pCO2 conditions.
  • Strong and rapid dissolved-particulate exchanges prevent a precise assessment of the effect of ocean acidification on the dissolution of nutrients (inorganic nitrogen, phosphate and iron) from dust in Low Nutrient Low Chlorophyll regions such as the Mediterranean Sea.

Abstract

The Mediterranean basin receives among the highest dust fluxes in the world ocean, and also appears to be one of the regions the most strongly impacted by ocean acidification. The aim of this study was to assess, on a short time scale (one-week), the effect of ocean acidification on the dissolution of nutrients (inorganic nitrogen, phosphate and iron) from Saharan dust. Three experiments were performed in three distinct seasons: in May, after the spring bloom with low autotrophic biomass, in September, at the end of the oligotrophic period, and in January, during the winter bloom. On each occasion, a dust flux of 10 g m-2 was simulated at the surface of two minicosms (tanks of ∼0.3 m3) filled with filtered (< 0.2 µm) seawater collected in the Bay of Villefranche (NW Mediterranean Sea). One minicosm served as a control and the other was acidified to reach a partial pressure of CO2 (pCO2) close to that projected for the end of this century (∼1250 μatm). Following a high-resolution sampling protocol, results showed that whatever the season and in situ biogeochemical conditions 1) all nitrogen from dust was soluble in seawater, allowing a large and stable increase in the stock of NOx (nitrate + nitrite) under the two pCO2 conditions (ambient and future), 2) transient increases in dissolved iron and phosphate concentrations were driven by scavenging processes, with a low dissolution percentage averaging 0.14 ± 0.08 and 4.7 ± 1.2%, respectively. While the absence of pCO2 effects on the release of atmospheric nitrogen was confirmed in the present study, no clear conclusion could be drawn for phosphate and dissolved iron as a consequence of very low concentrations and rapid (within less than 1 h) dissolved-particulate exchanges. Nevertheless, as the lifetime of these elements in solution is limited to a few hours, whatever the pH conditions, our results suggest that ocean acidification would have only a minor impact on their bioavailability for surface phytoplankton communities in such Low Nutrient Low Chlorophyll areas.

Continue reading ‘Atmospheric nutrients in seawater under current and high pCO2 conditions after Saharan dust deposition: results from three minicosm experiments’

Effects of in situ CO2 enrichment on epibiont settlement on artificial substrata within a Posidonia oceanica meadow

Highlights

  • Ocean acidification (OA) may cause community shifts by effecting early life stages.
  • pH was lowered in situ and maintained as an offset within a FOCE setup.
  • Settlement/colonization of molluscs and peracarid crustaceans were robust to OA.
  • Crustose coralline algae and calcifying polychaetes were vulnerable at early life.

Abstract

Alterations to colonization or early post-settlement stages may cause the reorganization of communities under future ocean acidification conditions. Yet, this hypothesis has been little tested by in situ pH manipulation. A Free Ocean Carbon Dioxide Enrichment (FOCE) system was used to lower pH by a ~ 0.3 unit offset within a partially enclosed portion (1.7 m3) of a Posidonia oceanica seagrass meadow (11 m depth) between 21 June and 3 November 2014. Epibiont colonization and early post settlement stages were assessed within the FOCE setup, as part of the larger community-level study, to better understand the outcome for a multispecies assemblage and the ecological processes that result in reported community shifts under altered carbonate chemistry. Two types of artificial collectors (tiles and scourers) were placed within three treatments: a pH-manipulated enclosure, an un-manipulated control enclosure, and an open plot in the ambient meadow. Tiles and scourers were collected after one to four months. Additionally, to see whether the outcome differed for communities in a later successional stage, previously settled scourer-collectors were also placed in the same three treatments. Enclosures acted to reduce settlement and migrant colonization. Scourers deployed for one to four months within the open-plot contained a community assemblage that could be distinguished from the assemblages within the enclosures. However, a comparison of enclosure assemblages on tiles showed evidence of a pH effect. There was lowered coverage of crustose coralline algae and fewer calcareous tube-forming polychaetes (Spirorbis sp. and Spirobranchus sp.) on tiles placed in the pH-manipulated enclosure compared to the un-manipulated enclosure. For assemblages in scourer collectors, shared and common taxa, in all treatments, were invertebrate polychaetes Psamathe fusca, Sphaerosyllis sp., Chrysopetalum sp., arthropods Harpacticoida, and Amphipoda, and the juvenile bivalve Lyonsia sp. Similar organism composition and abundance, as well as taxonomic richness and evenness, were found in scourers from both enclosures. Pre-settled scourers contained greater numbers of individuals and more calcified members, but the assemblage, as well as the growth rate of a juvenile bivalve Lyonsia sp., appeared unaffected by a two-month exposure to lowered pH and calcium carbonate saturation state. Results from this case study support the hypothesis that early stages of specific calcifiers (crustose coralline algae and calcareous tube-forming polychaetes) are sensitive to near future ocean acidification conditions yet suggest that negative effects on sessile micro-invertebrate assemblages will be minimal.

Continue reading ‘Effects of in situ CO2 enrichment on epibiont settlement on artificial substrata within a Posidonia oceanica meadow’


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