Posts Tagged 'protists'

The effects of environmental history and thermal stress on coral physiology and immunity

Rising ocean temperatures can induce the breakdown of the symbiosis between reef building corals and Symbiodinium in the phenomenon known as coral bleaching. Environmental history may, however, influence the response of corals to stress and affect bleaching outcomes. A suite of physiological and immunological traits was evaluated to test the effect of environmental history (low vs. high variable pCO2) on the response of the reef coral Montipora capitata to elevated temperature (24.5 °C vs. thermal ramping to 30.5 °C). Heating reduced maximum photochemical efficiency (Fv/Fm) and chlorophyll a but increased tissue melanin in corals relative to the ambient treatment, indicating a role of the melanin synthesis pathway in the early stages of thermal stress. However, interactions of environmental history and temperature treatment were not observed. Rather, parallel reaction norms were the primary response pattern documented across the two temperature treatments with respect to reef environmental history. Corals with a history of greater pCO2 variability had higher constitutive antioxidative and immune activity (i.e., catalase, superoxide dismutase, prophenoloxidase) and Fv/Fm, but lower melanin and chlorophyll a, relative to corals with a history of lower pCO2 variability. This suggests that reef environments with high magnitude pCO2 variability promote greater antioxidant and immune activity in resident corals. These results demonstrate coral physiology and immunity reflect environmental attributes that vary over short distances, and that these differences may buffer the magnitude of thermal stress effects on coral phenotypes.

Continue reading ‘The effects of environmental history and thermal stress on coral physiology and immunity’

Spiculosiphon oceana (Foraminifera) a new bio-indicator of acidic environments related to fluid emissions of the Zannone Hydrothermal Field (central Tyrrhenian Sea)


• Benthic foraminifers calcification process sensitive to ocean acidification.
Spiculosiphon oceana a proxy of acidic environments.
• New record of a shallow-water hydrothermal field in the western Mediterranean Sea.


The new record of a shallow-water submarine hydrothermal field (<150 m w.d.) in the western Mediterranean Sea (Tyrrhenian Sea, Italy) allows us to study CO2 fluid impact on benthic foraminifers. Benthic foraminifers calcification process is sensitive to ocean acidification and to local chemical and physical parameters of seawater and pore water. Thus, foraminifers can record specific environmental conditions related to hydrothermal fluids, but at present their response to such activity is poorly defined. The major outcome of this study is the finding of a very uncommon taxon for the Mediterranean Sea, i.e., the Spiculosiphon oceana, a giant foraminifer agglutinating spicules of sponges. This evidence, along with the strong decrease of calcareous tests in the foraminiferal assemblages associated to hydrothermal activity, provides new insights on the meiofauna living in natural stressed environment. In particular, observations obtained from this study allow us to consider S. oceana a potential tolerant species of high CO2 concentrations (about 2–4 times higher than the normal marine values) and a proxy of acidic environments as well as of recent ocean acidification processes.

Continue reading ‘Spiculosiphon oceana (Foraminifera) a new bio-indicator of acidic environments related to fluid emissions of the Zannone Hydrothermal Field (central Tyrrhenian Sea)’

Inorganic carbon is scarce for symbionts in scleractinian corals

Ocean acidification and changing sea surface temperatures stand to affect the interactions of corals and their Symbiodinium symbionts with regard to the inorganic carbon used for photosynthesis. However, there have been few investigations on the availability of dissolved inorganic carbon (DIC) for algal symbionts in hospite. This study compared the DIC-associated photosynthetic kinetic parameters of three Caribbean corals and their freshly isolated symbionts, as well as components of the DIC concentrating systems of both corals and symbionts. Species level differences were found in the extent of inorganic carbon saturation among the coral taxa studied. Only Orbicella faveolata was photosynthesizing at maximum rates under current seawater conditions, while Porites astreoides and Siderastrea radians were at or below half DIC saturation. O. faveolata also had significantly more external carbonic anhydrase activity, indicating that this species could produce more CO2 at the coral surface than P. astreoides or S. radians. In contrast and despite differences in Symbiodinium type, the symbionts of all the corals had a similar, very low DIC half saturation constant for photosynthesis and high levels of internal carbonic anhydrase activity, showing that they live in a carbon scarce environment and invest a great deal of energy in concentrating carbon at the site of photosynthesis. Considering the diffusional dynamics of the system and the relationship of host to symbiont kinetic parameters, the most likely cause of this scarcity is host regulation of DIC delivery to the symbionts.

Continue reading ‘Inorganic carbon is scarce for symbionts in scleractinian corals’

Coral physiology and microbiome dynamics under combined warming and ocean acidification

Rising seawater temperature and ocean acidification threaten the survival of coral reefs. The relationship between coral physiology and its microbiome may reveal why some corals are more resilient to these global change conditions. Here, we conducted the first experiment to simultaneously investigate changes in the coral microbiome and coral physiology in response to the dual stress of elevated seawater temperature and ocean acidification expected by the end of this century. Two species of corals, Acropora millepora containing the thermally sensitive endosymbiont C21a and Turbinaria reniformis containing the thermally tolerant endosymbiont Symbiodinium trenchi, were exposed to control (26.5°C and pCO2 of 364 μatm) and treatment (29.0°C and pCO2 of 750 μatm) conditions for 24 days, after which we measured the microbial community composition. These microbial findings were interpreted within the context of previously published physiological measurements from the exact same corals in this study (calcification, organic carbon flux, ratio of photosynthesis to respiration, photosystem II maximal efficiency, total lipids, soluble animal protein, soluble animal carbohydrates, soluble algal protein, soluble algal carbohydrate, biomass, endosymbiotic algal density, and chlorophyll a). Overall, dually stressed A. millepora had reduced microbial diversity, experienced large changes in microbial community composition, and experienced dramatic physiological declines in calcification, photosystem II maximal efficiency, and algal carbohydrates. In contrast, the dually stressed coral T. reniformis experienced a stable and more diverse microbiome community with minimal physiological decline, coupled with very high total energy reserves and particulate organic carbon release rates. Thus, the microbiome changed and microbial diversity decreased in the physiologically sensitive coral with the thermally sensitive endosymbiotic algae but not in the physiologically tolerant coral with the thermally tolerant endosymbiont. Our results confirm recent findings that temperature-stress tolerant corals have a more stable microbiome, and demonstrate for the first time that this is also the case under the dual stresses of ocean warming and acidification. We propose that coral with a stable microbiome are also more physiologically resilient and thus more likely to persist in the future, and shape the coral species diversity of future reef ecosystems.

Continue reading ‘Coral physiology and microbiome dynamics under combined warming and ocean acidification’

Incorporation of Mg, Sr, Ba, U and B in high-Mg calcite benthic foraminifers cultured under controlled pCO2

Measurement of elemental ratios (E/Ca) have been performed in two symbiont-bearing species of high-Mg calcite benthic foraminifers (hyaline, Baculogypsina sphaerulata and porcelaneous, Amphisorus hemprichii), cultured under five pCO2 levels, representing pre-industrial, modern and three predicted future values. E/Ca ratios were analyzed by Laser Ablation coupled with Inductively Coupled Plasma Mass Spectrometer (LA-ICP-MS). We measured several E/Ca such as Mg/Ca, Sr/Ca, Ba/Ca, U/Ca and B/Ca simultaneously. We observed that high-Mg calcite benthic foraminifers possess higher E/Ca than low-Mg calcite foraminifers, irrespective of their calcification mode (hyaline or porcelaneous). In both modes of calcification, Mg, Sr, Ba, U and B incorporation could be controlled by Rayleigh fractionation. However, more data is needed to validate and quantify the relative importance this process and closely investigate the presence/absence of other mechanism. Therefore, it highlights the need for a multi-elemental approach when looking at trace element incorporation. Finally, no significant relationship was observed between the different ratios and the pCO2 of the water, suggesting that none of the Mg/Ca, Sr/Ca, Ba/Ca, U/Ca and B/Ca is sensitive to bottom water pCO2 or pH in these species.

Continue reading ‘Incorporation of Mg, Sr, Ba, U and B in high-Mg calcite benthic foraminifers cultured under controlled pCO2’

Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment (update)

The Southern Ocean provides a vital service by absorbing about one-sixth of humankind’s annual emissions of CO2. This comes with a cost – an increase in ocean acidity that is expected to have negative impacts on ocean ecosystems. The reduced ability of phytoplankton and zooplankton to precipitate carbonate shells is a clearly identified risk. The impact depends on the significance of these organisms in Southern Ocean ecosystems, but there is very little information on their abundance or distribution. To quantify their presence, we used coulometric measurement of particulate inorganic carbonate (PIC) on particles filtered from surface seawater into two size fractions: 50–1000 µm to capture foraminifera (the most important biogenic carbonate-forming zooplankton) and 1–50 µm to capture coccolithophores (the most important biogenic carbonate-forming phytoplankton). Ancillary measurements of biogenic silica (BSi) and particulate organic carbon (POC) provided context, as estimates of the biomass of diatoms (the highest biomass phytoplankton in polar waters) and total microbial biomass, respectively. Results for nine transects from Australia to Antarctica in 2008–2015 showed low levels of PIC compared to Northern Hemisphere polar waters. Coccolithophores slightly exceeded the biomass of diatoms in subantarctic waters, but their abundance decreased more than 30-fold poleward, while diatom abundances increased, so that on a molar basis PIC was only 1 % of BSi in Antarctic waters. This limited importance of coccolithophores in the Southern Ocean is further emphasized in terms of their associated POC, representing less than 1 % of total POC in Antarctic waters and less than 10 % in subantarctic waters. NASA satellite ocean-colour-based PIC estimates were in reasonable agreement with the shipboard results in subantarctic waters but greatly overestimated PIC in Antarctic waters. Contrastingly, the NASA Ocean Biogeochemical Model (NOBM) shows coccolithophores as overly restricted to subtropical and northern subantarctic waters. The cause of the strong southward decrease in PIC abundance in the Southern Ocean is not yet clear. The poleward decrease in pH is small, and while calcite saturation decreases strongly southward, it remains well above saturation ( > 2). Nitrate and phosphate variations would predict a poleward increase. Temperature and competition with diatoms for limiting iron appear likely to be important. While the future trajectory of coccolithophore distributions remains uncertain, their current low abundances suggest small impacts on overall Southern Ocean pelagic ecology.

Continue reading ‘Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment (update)’

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

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