Posts Tagged 'otherprocess'

Does nutrient availability regulate seagrass response to elevated CO2?

Future increases in oceanic carbon dioxide concentrations (CO2(aq)) may provide a benefit to submerged plants by alleviating photosynthetic carbon limitation. However, other environmental factors (for example, nutrient availability) may alter how seagrasses respond to CO2(aq) by regulating the supply of additional resources required to support growth. Thus, questions remain in regard to how other factors influence CO2(aq) effects on submerged vegetation. This study factorially manipulated CO2(aq) and nutrient availability, in situ, within a subtropical seagrass bed for 350 days, and examined treatment effects on leaf productivity, shoot density, above- and belowground biomass, nutrient content, carbohydrate storage, and sediment organic carbon (Corg). Clear, open-top chambers were used to replicate CO2(aq) forecasts for the year 2100, whereas nutrient availability was manipulated via sediment amendments of nitrogen (N) and phosphorus (P) fertilizer. We provide modest evidence of a CO2 effect, which increased seagrass aboveground biomass. CO2(aq) enrichment had no effect on nutrient content, carbohydrate storage, or sediment Corg content. Nutrient addition increased leaf productivity and leaf N content, however did not alter above- or belowground biomass, shoot density, carbohydrate storage, or Corg content. Treatment interactions were not significant, and thus NP availability did not influence seagrass responses to elevated CO2(aq). This study demonstrates that long-term carbon enrichment may alter the structure of shallow seagrass meadows, even in relatively nutrient-poor, oligotrophic systems.

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Impact of ocean acidification and warming on the diversity and the functioning of macroalgal communities (full thesis in French)

Predicted ocean acidification and warming for the end of the century may have drastic consequences on the structure and functioning of marine ecosystems. However, a lack of knowledge persists on the impact of future changes on the response of marine communities. This thesis aims to provide new understanding of the impact of ocean acidification and warming at the community level. For this, two ecosystems have been considered: rockpools, characterized by high physico-chemical variations, and maerl beds, with smaller variations. In the laboratory, artificial assemblages were created from the main calcareous and fleshy macroalgal and grazer species present in these two ecosystems. Created assemblages have been subjected to ambient and future temperature and pCO2 conditions. Ocean acidification and warming altered the structure and functioning of maerl bed assemblages, through an increase in the productivity of non-calcareous macroalgae and a decline in maërl calcification rates. The physiology of grazers is negatively impacted by future changes, which altered assemblages’ trophic structure. On the other hand, ocean acidification and warming had no effect on the productivity of rockpool assemblages. The highly variable environment may thus increase the resistance of rockpool communities to future changes, compared to communities from more stable environments, such as maerl beds.

Continue reading ‘Impact of ocean acidification and warming on the diversity and the functioning of macroalgal communities (full thesis in French)’

The response of the diatom Asterionllopsis glacialis to variations in CO2 and nitrate availability

Atmospheric CO2 levels have been rapidly increasing since the 280 ppm (ppm-parts per million) found previous to the industrial revolution (IPCC 2014). In 2010 the atmospheric CO2 was ~380 ppm (IPCC 2014). In May 2018 the Mauna Loa Observatory in Hawaii reported 411.21 ppm of CO2 at the surface ocean (Mooney 2018). These rapid changes in the atmosphere also affect ocean chemistry. Surface ocean pH has been rather stable before industrialization over the last 800 000 years, averaging 8.2 at the surface water. Since the industrial revolution, the pH has dropped ~0.1 units, so the present day value is ~8.1 (Gattuso, Hansson 2011; Riebesell et al. 2010). Based on business as-usual scenario, atmospheric CO2 levels are expected to approach 800 ppm by the end of the century, which means that pH would drop further 0.3 to 0.5 units and reach 7.8 pH units (Feely et al. 2009, IPCC report 2014). Finally, the changes in ocean chemistry are not happening everywhere at the same pace. For example, in areas where the water temperature is lower, like the Arctic Ocean, CO2 levels and concomitant acidification is increasing more rapidly (CO2 dissolves better in colder water). This makes the Arctic one of the most efficient areas for the sink of anthropogenic CO2 in the global ocean (Slagstad et al. 2011).

Continue reading ‘The response of the diatom Asterionllopsis glacialis to variations in CO2 and nitrate availability’

Impact of carbonate saturation on large Caribbean benthic foraminifera assemblages

Increasing atmospheric carbon dioxide and its dissolution in seawater have reduced ocean pH and carbonate ion concentration with potential implications to calcifying organisms. To assess the response of Caribbean benthic foraminifera to low carbonate saturation conditions, we analyzed benthic foraminifera abundance and relative distribution in proximity to low carbonate saturation submarine springs and at adjacent control sites. Our results show that the total abundance of benthic foraminifera is significantly lower at the low pH low calcite saturation submarine springs than at control sites, despite higher concentrations of inorganic carbon at the spring sites. The relative abundance of symbiont-bearing foraminifera and agglutinated foraminifera was higher at the low pH low calcite saturation submarine springs compared to control sites. These differences indicate that non-symbiont bearing heterotrophic calcareous foraminifera are more sensitive to the effects of ocean acidification than non-calcifying and symbiont bearing foraminifera, suggesting that future ocean acidification may impact natural benthic foraminifera populations.

Continue reading ‘Impact of carbonate saturation on large Caribbean benthic foraminifera assemblages’

Coccolithophore community response along a natural CO2 gradient off Methana (SW Saronikos Gulf, Greece, NE Mediterranean)

A natural pH gradient caused by marine CO2 seeps off the Methana peninsula (Saronikos Gulf, eastern Peloponnese peninsula) was used as a natural laboratory to assess potential effects of ocean acidification on coccolithophores. Coccolithophore communities were therefore investigated in plankton samples collected during September 2011, September 2016 and March 2017. The recorded cell concentrations were up to ~50 x103 cells/l, with a high Shannon index of up to 2.8, along a pH gradient from 7.61 to 8.18, with values being occasionally <7. Numerous holococcolithophore species represented 60–90% of the surface water assemblages in most samples during September samplings. Emiliania huxleyi was present only in low relative abundances in September samples, but it dominated in March assemblages. Neither malformed nor corroded coccolithophores were documented. Changes in the community structure can possibly be related to increased temperatures, while the overall trend associates low pH values with high cell densities. Our preliminary results indicate that in long-termed acidified, warm and stratified conditions, the study of the total coccolithophore assemblage may prove useful to recognize the intercommunity variability, which favors the increment of lightly calcified species such as holococcolithophores.

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Geographical CO2 sensitivity of phytoplankton correlates with ocean buffer capacity

Accumulation of anthropogenic CO2 is significantly altering ocean chemistry. A range of biological impacts resulting from this oceanic CO2 accumulation are emerging, however, the mechanisms responsible for observed differential susceptibility between organisms and across environmental settings remain obscure. A primary consequence of increased oceanic CO2 uptake is a decrease in the carbonate system buffer capacity, which characterizes the system’s chemical resilience to changes in CO2, generating the potential for enhanced variability in pCO2 and the concentration of carbonate [urn:x-wiley:13541013:media:gcb14324:gcb14324-math-0001], bicarbonate [urn:x-wiley:13541013:media:gcb14324:gcb14324-math-0002], and protons [H+] in the future ocean. We conducted a meta‐analysis of 17 shipboard manipulation experiments performed across three distinct geographical regions that encompassed a wide range of environmental conditions from European temperate seas to Arctic and Southern oceans. These data demonstrated a correlation between the magnitude of natural phytoplankton community biological responses to short‐term CO2 changes and variability in the local buffer capacity across ocean basin scales. Specifically, short‐term suppression of small phytoplankton (<10 μm) net growth rates were consistently observed under enhanced pCO2within experiments performed in regions with higher ambient buffer capacity. The results further highlight the relevance of phytoplankton cell size for the impacts of enhanced pCO2 in both the modern and future ocean. Specifically, cell size‐related acclimation and adaptation to regional environmental variability, as characterized by buffer capacity, likely influences interactions between primary producers and carbonate chemistry over a range of spatio‐temporal scales.

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Baltic Sea diazotrophic cyanobacterium is negatively affected by acidification and warming

Nitrogen fixation is a key source of nitrogen in the Baltic Sea which counteracts nitrogen loss processes in the deep anoxic basins. Laboratory and field studies have indicated that single-strain nitrogen-fixing (diazotrophic) cyanobacteria from the Baltic Sea are sensitive to ocean acidification and warming, 2 drivers of marked future change in the marine environment. Here, we enclosed a natural plankton community in 12 indoor mesocosms (volume ~1400 l) and manipulated partial pressure of carbon dioxide ( pCO2) in seawater to yield 6 CO2 treatments with 2 different temperature treatments (16.6°C and 22.4°C, pCO2 range = 360-2030 µatm). We followed the filamentous, heterocystous diazotrophic cyanobacteria community (Nostocales, primarily Nodularia spumigena) over 4 wk. Our results indicate that heterocystous diazotrophic cyanobacteria may become less competitive in natural plankton communities under ocean acidification. Elevated CO2 had a negative impact on Nodularia sp. biomass, which was exacerbated by warming. Our results imply that Nodularia sp. may contribute less to new nitrogen inputs in the Baltic Sea in the future.

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Ocean acidification in the IPCC AR5 WG II

OUP book