Posts Tagged 'BRcommunity'

The combined effects of ocean warming and acidification on shallow-water meiofaunal assemblages

Highlights

  • Higher seawater temperature did not effect meiofaunal abundance.
  • Lower seawater pH did reduce meiofaunal abundance and species richness.
  • Nematode assemblages showed increased dominance under a future OW/OA scenario.


Abstract

Climate change due to increased anthropogenic CO2 in the atmosphere is causing an increase in seawater temperatures referred to as ocean warming and a decrease in seawater pH, referred to as ocean acidification. The meiofauna play an important role in the ecology of marine ecosystems and the functions they provide. Using microcosms, meiofaunal assemblages were exposed to two temperatures (15 and 19 °C) and two pHs (pCO2 of 400 and 1000 ppm), both individually and in combination, for a period of 90 days. The hypothesis that increased temperature will increase meiofaunal abundance was not supported. The hypothesis that a reduced pH will reduce meiofaunal abundance and species richness was supported. The combination of future conditions of temperature and pH (19 °C and pCO2 of 1000 ppm) did not affect overall abundance but the structure of the nematode assemblage changed becoming dominated by a few opportunistic species.

Continue reading ‘The combined effects of ocean warming and acidification on shallow-water meiofaunal assemblages’

Reviews and syntheses: Ice acidification, the effects of ocean acidification on sea ice microbial communities (update)

Sea ice algae, like some coastal and estuarine phytoplankton, are naturally exposed to a wider range of pH and CO2 concentrations than those in open marine seas. While climate change and ocean acidification (OA) will impact pelagic communities, their effects on sea ice microbial communities remain unclear.

Sea ice contains several distinct microbial communities, which are exposed to differing environmental conditions depending on their depth within the ice. Bottom communities mostly experience relatively benign bulk ocean properties, while interior brine and surface (infiltration) communities experience much greater extremes.

Most OA studies have examined the impacts on single sea ice algae species in culture. Although some studies examined the effects of OA alone, most examined the effects of OA and either light, nutrients or temperature. With few exceptions, increased CO2 concentration caused either no change or an increase in growth and/or photosynthesis. In situ studies on brine and surface algae also demonstrated a wide tolerance to increased and decreased pH and showed increased growth at higher CO2 concentrations. The short time period of most experiments (< 10 days), together with limited genetic diversity (i.e. use of only a single strain), however, has been identified as a limitation to a broader interpretation of the results.

While there have been few studies on the effects of OA on the growth of marine bacterial communities in general, impacts appear to be minimal. In sea ice also, the few reports available suggest no negative impacts on bacterial growth or community richness.

Sea ice ecosystems are ephemeral, melting and re-forming each year. Thus, for some part of each year organisms inhabiting the ice must also survive outside of the ice, either as part of the phytoplankton or as resting spores on the bottom. During these times, they will be exposed to the full range of co-stressors that pelagic organisms experience. Their ability to continue to make a major contribution to sea ice productivity will depend not only on their ability to survive in the ice but also on their ability to survive the increasing seawater temperatures, changing distribution of nutrients and declining pH forecast for the water column over the next centuries.
Continue reading ‘Reviews and syntheses: Ice acidification, the effects of ocean acidification on sea ice microbial communities (update)’

Ocean acidification experiments in large-scale mesocosms reveal similar dynamics of dissolved organic matter production and biotransformation

Dissolved organic matter (DOM) represents a major reservoir of carbon in the oceans. Environmental stressors such as ocean acidification (OA) potentially affect DOM production and degradation processes, e.g., phytoplankton exudation or microbial uptake and biotransformation of molecules. Resulting changes in carbon storage capacity of the ocean, thus, may cause feedbacks on the global carbon cycle. Previous experiments studying OA effects on the DOM pool under natural conditions, however, were mostly conducted in temperate and coastal eutrophic areas. Here, we report on OA effects on the existing and newly produced DOM pool during an experiment in the subtropical North Atlantic Ocean at the Canary Islands during an (1) oligotrophic phase and (2) after simulated deep water upwelling. The last is a frequently occurring event in this region controlling nutrient and phytoplankton dynamics. We manipulated nine large-scale mesocosms with a gradient of pCO2 ranging from ~350 up to ~1,030 μatm and monitored the DOM molecular composition using ultrahigh-resolution mass spectrometry via Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). An increase of 37 μmol L−1 DOC was observed in all mesocosms during a phytoplankton bloom induced by simulated upwelling. Indications for enhanced DOC accumulation under elevated CO2 became apparent during a phase of nutrient recycling toward the end of the experiment. The production of DOM was reflected in changes of the molecular DOM composition. Out of the 7,212 molecular formulae, which were detected throughout the experiment, ~50% correlated significantly in mass spectrometric signal intensity with cumulative bacterial protein production (BPP) and are likely a product of microbial transformation. However, no differences in the produced compounds were found with respect to CO2 levels. Comparing the results of this experiment with a comparable OA experiment in the Swedish Gullmar Fjord, reveals similar succession patterns for individual compound pools during a phytoplankton bloom and subsequent accumulation of these compounds were observed. The similar behavior of DOM production and biotransformation during and following a phytoplankton bloom irrespective of plankton community composition and CO2 treatment provides novel insights into general dynamics of the marine DOM pool.

Continue reading ‘Ocean acidification experiments in large-scale mesocosms reveal similar dynamics of dissolved organic matter production and biotransformation’

Iron sources alter the response of Southern Ocean phytoplankton to ocean acidification

The rise in anthropogenic CO2 and the associated ocean acidification (OA) will change trace metal solubility and speciation, potentially altering Southern Ocean (SO) phytoplankton productivity and species composition. As iron (Fe) sources are important determinants of Fe bioavailability, we assessed the effect of Fe-laden dust versus inorganic Fe (FeCl3) enrichment under ambient and high pCO2 levels (390 and 900 μatm) in a naturally Fe-limited SO phytoplankton community. Despite similar Fe chemical speciation and net particulate organic carbon (POC) production rates, CO2-dependent species shifts were controlled by Fe sources. Final phytoplankton communities of both control and dust treatments were dominated by the same species, with an OA-dependent shift from the diatom Pseudo nitzschia prolongatoides towards the prymnesiophyte Phaeocystis antarctica. Addition of FeCl3 resulted in high abundances of Nitzschia lecointei and Chaetoceros neogracilis under ambient and high pCO2, respectively. These findings reveal that both the characterization of the phytoplankton community at the species level and the use of natural Fe sources are essential for a realistic projection of the biological carbon pump in the Fe-limited pelagic SO under OA. As dust deposition represents a more realistic scenario for the Fe-limited pelagic SO under OA, unaffected net POC production and dominance of P. antarctica can potentially weaken the export of carbon and silica in the future.

Continue reading ‘Iron sources alter the response of Southern Ocean phytoplankton to ocean acidification’

Spatio-temporal variation of phytoplankton communities along a salinity and pH gradient in a tropical estuary (Brunei, Borneo, South East Asia)

Characterizing phytoplankton communities is essential to understanding the ecological functioning of pelagic marine systems. Nevertheless, our knowledge of phytoplankton communities is still inadequate for many tropical habitats, including estuaries. It is assumed that highly turbid tropical estuaries often experience acidification due to anthropogenic inputs, microbial degradation, run-off from acidic sulphate soils, and low buffer capacity characteristic for all estuarine systems. Here, we describe phytoplankton communities from the turbid, acidified, and euthrophised estuary of Brunei River (South East Asia). The four selected sampling stations represented gradients of salinity (0.4 – 28.5 PSU) and pH (5.87 – 8.06). A total of 26 microalgal families of phytoplankton (22 genera of diatoms, 7 of dinoflagellates, and 1 of ciliates) were recorded in the survey carried out over one year. The highest density was recorded at an intermediate station along the gradient (up to 9107 cells ml-1), whereas the lowest diversity was found at the least saline and most acidic station (7-1146 cells ml-1). Diatoms were a dominant component of the communities, with Nitzschia spp., Rhizosolenia spp., and Leptocylindrus sp. reaching the highest abundances. Salinity, pH and dissolved oxygen (DO) were positively correlated with the plankton abundances and typically declined landwards. Statistical analyses indicated that phytoplankton communities were strongly influenced by the effect of season (30 % of the total variance in phytoplankton data explained) and sampling site (20 %). The joint effect of pH and salinity and of pH and temperature explained 16.7 % and 17.5 % of the total observed variation, respectively.

Continue reading ‘Spatio-temporal variation of phytoplankton communities along a salinity and pH gradient in a tropical estuary (Brunei, Borneo, South East Asia)’

Alterations in microbial community composition with increasing fCO2: a mesocosm study in the eastern Baltic Sea (update)

Ocean acidification resulting from the uptake of anthropogenic carbon dioxide (CO2) by the ocean is considered a major threat to marine ecosystems. Here we examined the effects of ocean acidification on microbial community dynamics in the eastern Baltic Sea during the summer of 2012 when inorganic nitrogen and phosphorus were strongly depleted. Large-volume in situ mesocosms were employed to mimic present, future and far future CO2 scenarios. All six groups of phytoplankton enumerated by flow cytometry ( <  20 µm cell diameter) showed distinct trends in net growth and abundance with CO2 enrichment. The picoeukaryotic phytoplankton groups Pico-I and Pico-II displayed enhanced abundances, whilst Pico-III, Synechococcus and the nanoeukaryotic phytoplankton groups were negatively affected by elevated fugacity of CO2 (fCO2). Specifically, the numerically dominant eukaryote, Pico-I, demonstrated increases in gross growth rate with increasing fCO2 sufficient to double its abundance. The dynamics of the prokaryote community closely followed trends in total algal biomass despite differential effects of fCO2 on algal groups. Similarly, viral abundances corresponded to prokaryotic host population dynamics. Viral lysis and grazing were both important in controlling microbial abundances. Overall our results point to a shift, with increasing fCO2, towards a more regenerative system with production dominated by small picoeukaryotic phytoplankton.

Continue reading ‘Alterations in microbial community composition with increasing fCO2: a mesocosm study in the eastern Baltic Sea (update)’

The organizing effects of elevated CO2 on competition among estuarine primary producers

Fossil fuel combustion, eutrophication, and upwelling introduce excess CO2 into coastal zones. The extent to which marine autotrophs may benefit from elevated CO2 will be a function of their carbon limitation and, among other factors, competition with other primary producers. Here, we report on experiments performed with North Atlantic species of Ulva and Gracilaria grown in situ or exposed to ambient (~400 µatm) and elevated pCO2 (~2500 µatm) and/or subjected to competition with each other and/or with natural plankton assemblages. Elevated pCO2significantly increased the growth rates of Gracilaria and Ulva and yielded significant declines in tissue δ13C, suggesting that increased growth was associated with increased CO2 use relative to HCO3−. Gracilaria growth was unaffected by competition with plankton or Ulva, while Ulva experienced significantly reduced growth when competing with Gracilaria or plankton. Dinoflagellates experienced significantly increased growth when exposed to elevated pCO2 but significantly slower growth when competing with Gracilaria. Elevated carbon-to-nitrogen ratios among macroalgae suggested that competition for nitrogen also shaped interactions among autotrophs, particularly Ulva. While some estuarine autotrophs benefit from elevated pCO2, the benefit can change when direct competition with other primary producers is considered with Gracilaria outcompeting Ulva and dinoflagellates outcompeting diatoms under elevated pCO2.

Continue reading ‘The organizing effects of elevated CO2 on competition among estuarine primary producers’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book