Posts Tagged 'Mediterranean'

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’

The sibling polychaetes Platynereis dumerilii and Platynereis massiliensis in the Mediterranean Sea: are phylogeographic patterns related to exposure to ocean acidification?

High pCO2 environments, such as volcanic carbon dioxide (CO2) vents, which mimic predicted near-future scenarios of ocean acidification (OA), offer an opportunity to examine effects of low pH conditions on marine biodiversity and adaptation/acclimatization of marine organisms to such conditions. Based on previous field studies in these systems, it is predicted that the stress owing to increasing CO2 concentrations favours the colonization by invertebrate species with a brooding habit. The goal of this study was to investigate the relative occurrence of the two sibling species Platynereis dumerilii (Audouin & Milne-Edwards, 1834) (free spawner) and Platynereis massiliensis (Moquin-Tandon, 1869) (egg brooder) in two shallow CO2 vents off Ischia and Vulcano islands (Italy, Tyrrhenian Sea), and in various areas with ambient pH conditions, where they represent one of the dominant genera. Phylogeographic analyses were integrated with reproductive biology and life-history observations on some selected populations thriving in the vent areas. This approach revealed the presence of four distinct Platynereis clades. Whereas two clades primarily inhabit CO2 vents and are presumably all brooders, the other two clades dominate the non-acidified sites and appear to be epitokous free spawners. We postulate that one of the brooding, vent-inhabiting clades represents P. massiliensis and one of the free spawning, non-vent-inhabiting clades represents P. dumerilii, although confirmation of the species status with sequence data from the respective-type localities would be desirable.

Continue reading ‘The sibling polychaetes Platynereis dumerilii and Platynereis massiliensis in the Mediterranean Sea: are phylogeographic patterns related to exposure to ocean acidification?’

Coccolithophore haploid and diploid distribution patterns in the Mediterranean Sea: can a haplo-diploid life cycle be advantageous under climate change?

Coccolithophores are unicellular pelagic algae, capable of calcification. In the Mediterranean Sea, several species have a well-known haplo-diploid life cycle, alternating the production of different types of calcite plates, the holo- and hetero-coccoliths. We analyzed the distribution of both phases along a W-E Mediterranean transect during April 2011 and May 2013 (spring season), following strong environmental gradients in salinity, oxygen and nutrient concentration, temperature, carbonate chemistry and fluorescence. The proportion of holococcolithophores:heterococcolithophores of selected species varies not only vertically through the water column, but also longitudinally, following the main environmental gradients. Based on the environmental affinities of the coccolithophore life phases, we conclude that a dimorphic life cycle might provide the ability to adapt to the south-eastern (SE) Mediterranean environment, in conditions characterized by surface water with relatively high calcite saturation state, high temperature, stratification and nutrient limitation, and support the survival of species whose diploid phases are in contrast adapted to Atlantic or south-western (SW) Mediterranean conditions. Thus, a haplo-diploid life cycle could provide a way to adapt to environmental changes.

Continue reading ‘Coccolithophore haploid and diploid distribution patterns in the Mediterranean Sea: can a haplo-diploid life cycle be advantageous under climate change?’

The influence of high pCO2 on otolith shape, chemical and carbon isotope composition of six coastal fish species in a Mediterranean shallow CO2 vent

Naturally acidified environments, such as CO2 vents, are important sites to evaluate the potential effects of increased ocean acidification on marine ecosystems and biota. Here we assessed the effect of high CO2/low pH on otolith shape and chemical composition of six coastal fish species (Chromis chromis, Coris julis, Diplodus vulgaris, Gobius bucchichi, Sarpa salpa, Symphodus ocellatus) in a Mediterranean shallow CO2 vent. Taking into consideration the major and trace elements found near the vent and the gradient of dissolved inorganic carbon, we compared the otolith chemical signatures of fish exposed long-term to elevated CO2 emissions and reduced pH (mean pH 7.8) against fish living in two control sites (mean pH 8.2). A number of element:Ca ratios (Na:Ca, Mg:Ca, Mn:Ca, Cu:Ca, Zn:Ca, Sr:Ca, Ba:Ca and Pb:Ca), along with isotope ratios, were measured in otoliths (δ13C and δ18O) and water (δ13CDIC) samples. Additionally, we performed otolith outline shape and morphometric analysis to evaluate the effect of high CO2/low pH. We observed species-specific responses with regards to both shape and chemical signatures. Significant differences among sites were found in otolith shape (elliptical Fourier descriptors) of G. bucchichi and D. vulgaris. Elemental and isotopic signatures were also significantly different in these site attached species, though not for the other four. Overall, the carbon isotopic composition seems a good proxy to follow pH gradient in naturally acidified area. Ultimately, besides improving our knowledge of the effects of high CO2/low pH on otoliths, the present results contribute to our understanding on their use as natural tags.

Continue reading ‘The influence of high pCO2 on otolith shape, chemical and carbon isotope composition of six coastal fish species in a Mediterranean shallow CO2 vent’

Morphological response of the larvae of Arbacia lixula to near-future ocean warming and acidification

The distribution of the sea urchin Arbacia lixula, a warm affinity species, has been expanding in the Mediterranean Sea. To address questions on potential for future success of this species in the region, the thermotolerance of larval development was investigated in context of regional warming. The larvae were reared in present day spawning period (20 °C) and warming conditions (+4 = 24 and +6 = 26 °C). As the calcifying larvae of sea urchins are vulnerable to stunted growth caused by ocean acidification, the impact of lower pH (−0.3 pH units) on larval development was also investigated in combination with warming. Morphological traits of the larvae, post-oral length arms, overall length of larvae and body length, were affected by increased temperature across pH treatments, indicating that for the larvae of southern Mediterranean population here, 24 °C appears to approximate the optimal temperature for development. A slightly negative effect of pH was evident. Increased temperature ameliorated the stunting effect of acidification on growth. The thermal tolerance of A. lixula development overlaps with projections for warming in the region by 2100 and also indicates that this species has acclimatized or adapted its reproductive biology to the broad environmental conditions of the Mediterranean Sea. Due to the broad thermal range (∼10 °C) of development of A. lixula across its distribution, this species is likely to be a winner in the climate change stakes. The broad thermal tolerance of the larvae is likely to assure population connectivity between Mediterranean sub-basins populations. The continued success of A. lixula can have a strong consequences for the ecological structure of Mediterranean rocky habitat.

Continue reading ‘Morphological response of the larvae of Arbacia lixula to near-future ocean warming and acidification’

Ocean acidification as a driver of community simplification via the collapse of higher-order and rise of lower-order consumers

Increasing oceanic uptake of CO2 is predicted to drive ecological change as both a resource (i.e. CO2 enrichment on primary producers) and stressor (i.e. lower pH on consumers). We use the natural ecological complexity of a CO2 vent (i.e. a seagrass system) to assess the potential validity of conceptual models developed from laboratory and mesocosm research. Our observations suggest that the stressor-effect of CO2enrichment combined with its resource-effect drives simplified food web structure of lower trophic diversity and shorter length. The transfer of CO2 enrichment from plants to herbivores through consumption (apparent resource-effect) was not compensated by predation, because carnivores failed to contain herbivore outbreaks. Instead, these higher-order consumers collapsed (apparent stressor-effect on carnivores) suggesting limited trophic propagation to predator populations. The dominance of primary producers and their lower-order consumers along with the loss of carnivores reflects the duality of intensifying ocean acidification acting both as resource-effect (i.e. bottom-up control) and stressor-effect (i.e. top-down control) to simplify community and trophic structure and function. This shifting balance between the propagation of resource enrichment and its consumption across trophic levels provides new insights into how the trophic dynamics might stabilize against or propagate future environmental change.

Continue reading ‘Ocean acidification as a driver of community simplification via the collapse of higher-order and rise of lower-order consumers’

Effects of ocean acidification on the shells of four Mediterranean gastropod species near a CO2 seep

Marine CO2 seeps allow the study of the long-term effects of elevated pCO2 (ocean acidification) on marine invertebrate biomineralization. We investigated the effects of ocean acidification on shell composition and structure in four ecologically important species of Mediterranean gastropods (two limpets, a top-shell snail, and a whelk). Individuals were sampled from three sites near a volcanic CO2 seep off Vulcano Island, Italy. The three sites represented ambient (8.15 pH), moderate (8.03 pH) and low (7.73 pH) seawater mean pH. Shell mineralogy, microstructure, and mechanical strength were examined in all four species. We found that the calcite/aragonite ratio could vary and increased significantly with reduced pH in shells of one of the two limpet species. Moreover, each of the four gastropods displayed reductions in either inner shell toughness or elasticity at the Low pH site. These results suggest that near-future ocean acidification could alter shell biomineralization and structure in these common gastropods.

Continue reading ‘Effects of ocean acidification on the shells of four Mediterranean gastropod species near a CO2 seep’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book