Posts Tagged 'field'



Polar opposites; bacterioplankton susceptibility and mycoplankton resistance to ocean acidification

Microorganisms form the basis of ocean ecosystems yet the effects of perturbations such as decreasing pH on microbial community structure, interactions and functionality remain compared to multicellular organisms. Using an experimental manipulation of Southern Ocean seawater, we subjected bacterioplankton and mycoplankton to artificial pH decreases, which are predicted to occur in the future. We show that acidification led to substantial increases of bacterioplankton diversity, while in contrast it had no effect on mycoplankton diversity. Our analyses revealed a loss of putative keystone taxa and a decrease in predicted community interactions as a response to lower pH levels. Bacterioplankton shifted from generalist to specialist community members, suggesting a specific stress response to unfavourable conditions. In addition, enzyme activities involved in nitrogen acquisition were lower at reduced pH levels, suggesting altered organic matter cycling in a more acidic ocean. Our findings suggest that bacterioplankton and mycoplankton may respond differentially to future ocean acidification, with potentially negative impacts on community structure and biogeochemical cycling in the Southern Ocean.

Continue reading ‘Polar opposites; bacterioplankton susceptibility and mycoplankton resistance to ocean acidification’

A unique temperate rocky coastal hydrothermal vent system (Whakaari–White Island, Bay of Plenty, New Zealand): constraints for ocean acidification studies

In situ effects of ocean acidification are increasingly studied at submarine CO2 vents. Here we present a preliminary investigation into the water chemistry and biology of cool temperate CO2 vents near Whakaari–White Island, New Zealand. Water samples were collected inside three vent shafts, within vents at a distance of 2 m from the shaft and at control sites. Vent samples contained both seawater pH on the total scale (pHT) and carbonate saturation states that were severely reduced, creating conditions as predicted for beyond the year 2100. Vent samples showed lower salinities, higher temperatures and greater nutrient concentrations. Sulfide levels were elevated and mercury levels were at concentrations considered toxic at all vent and control sites, but stable organic and inorganic ligands were present, as deduced from Cu speciation data, potentially mediating harmful effects on local organisms. The biological investigations focused on phytoplankton, zooplankton and macroalgae. Interestingly, we found lower abundances but higher diversity of phytoplankton and zooplankton at sites in the direct vicinity of Whakaari. Follow-up studies will need a combination of methods and approaches to attribute observations to specific drivers. The Whakaari vents represent a unique ecosystem with considerable biogeochemical complexity, which, like many other vent systems globally, require care in their use as a model of ‘future oceans’.

Continue reading ‘A unique temperate rocky coastal hydrothermal vent system (Whakaari–White Island, Bay of Plenty, New Zealand): constraints for ocean acidification studies’

Carbon dioxide fluxes from two typical mariculture polyculture systems in coastal China

Highlights

• Among the first studies on CO2 flux from two typical seawater aquaculture ponds in 2 consecutive years.

• Water pH seemed like a stable indicator for CO2 flux from mariculture system and Chlorophyll a concentration was a key factor regulating the CO2 flux.

• Subsequent decreasing in water pH and Chlorophyll a concentration after farming short-necked clam was supposed to be the main contributor turning the bi-species polyculture system of swimming crab with kuruma shrimp from a CO2 sink into a CO2 source.

Abstract

During the farming season of 2013 and 2014, carbon dioxide (CO2) fluxes at the water-air interface were determined from two typical seawater polyculture systems. The mean CO2 fluxes of 2013 and 2014 were − 0.316 ± 0.0674 μmol m−2 s−1 and -0.173 ± 0.242 μmol m−2 s−1 in the bi-species polyculture system of swimming crab (Portunus trituberculatus) with kuruma shrimp (Marsupenaeus japonicus) (PM) and 0.249 ± 0.251 μmol m−2 s−1 and 0.426 ± 0.151 μmol m−2 s−1 in the tri-species polyculture system of swimming crab with shrimp and short-necked clam (Ruditapes philippinarum) (PMR) (Negative flux values refer to CO2 uptake and positive values refer to CO2 emission). During the farming season, the CO2 budgets in PM and PMR were − 113.1 g CO2 m−2 and 154.0 g CO2 m−2, respectively. Water pH seemed like a stable indicator for CO2 flux and Chlorophyll a concentration was a key factor regulating the CO2 flux. Subsequent decreasing in water pH and Chl a concentration was supposed to be the main contributor changing the carbon source/sink function from a CO2 sink of PM to a CO2 source of PMR. Under the condition of current study, pH of 8.26 could be considered to be the critical value between influxes and effluxes in seawater crab-shrimp and crab-shrimp-clam polyculture systems.

Continue reading ‘Carbon dioxide fluxes from two typical mariculture polyculture systems in coastal China’

Quantifying the effect of anthropogenic climate change on calcifying plankton

Widely regarded as an imminent threat to our oceans, ocean acidification has been documented in all oceanic basins. Projected changes in seawater chemistry will have catastrophic biotic effects due to ocean acidification hindering biogenic carbonate production, which will in turn lead to substantial changes in marine ecosystems. However, previous attempts to quantify the effect of acidification on planktonic calcifying organisms has relied on laboratory based studies with substantial methodological limitations. This has been overcome by comparing historic plankton tows from the seminal HMS Challenger Expedition (1872–1876) with the recent Tara Oceans expedition material (2009–2016). Nano CT-scans of selected equatorial Pacific Ocean planktonic foraminifera, have revealed that all modern specimens had up to 76% thinner shells than their historic counterparts. The “Challenger Revisited” project highlights the potential of historic ocean collections as a tool to investigate ocean acidification since the early Industrial Revolution. Further analyses of such biotic archives will enable researchers to quantify the effects of anthropogenic climate change across the globe.

Continue reading ‘Quantifying the effect of anthropogenic climate change on calcifying plankton’

The effects of ocean acidification, warming and enhanced nutrients on a Wadden Sea community – examined with mesocosm experiments

Ocean acidification and global warming are known as two of the most crucial factors impacting marine ecosystems worldwide. While most investigations tested short-term impacts of single environmental drivers (e.g. temperature, salintiy) on single species, studies on the combined effect of multiple drivers on a multi-species assemblage in different seasons, which is much more realistic and relevant, are still scarce. Therefore, an experimental mesocosm facility was built to gain information on community changes under the impacts from multiple drivers. In three consecutive experiments, in spring, summer and autumn 2014, compartments of an intertidal macroalgae-mussel community from the Wadden Sea were incubated for 8 to 11 weeks within a large-scale mesocosm facility (Sylt Benthic Mesocosm). In the experiments four different treatments were applied: Ambient, nutrient enrichment (N; doubled natural summer nutrient concentration), warming in combination with acidification (OAW; ambient + 5°C and 1000ppm), and a combination of all three drivers (OAW+N). To find seasonal effects, we compared the responses of (OAW) to that of the ambient treatment in spring, summer and autumn. Carbon flows within the food web of the enclosed species assemblage were analysed by a holistic, static modelling approach (Ecological Network Analysis, ENA). The combined effects of ocean warming and acidification decreased the biomass of the main grazers and the macrophyte Fucus vesiculosus, while epiphytes massively increased due to an altered top-down control during summer. This creates a bottle neck within the energy flow between the first two trophic levels and let less energy pass to higher trophic levels. Enriched nutrients alone did not affect the system substantially, but especially grazers seem to benefit from enriched nutrient concentrations. The effects of climate change on the investigated Wadden Sea community strongly depends on the investigated season. In spring and autumn, OAW affected less or even promoted the system by increased energy flows between the trophic levels. In summer the opposite was found, with decreased energy flow, hampered top-down control and a reduced trophic efficiency, that could propagate through the whole food web and alter the structure and functioning of the investigated community. The Analysis ENA showed a lower relative ascendancy and the trend to an increasing flow diversity, as the result of a high number of multiple pathways between the system components. Theoretically, the resilience of the system shows a tendency to increase and the capability of withstanding external disturbances under OAW as compared to an unstressed system.

Continue reading ‘The effects of ocean acidification, warming and enhanced nutrients on a Wadden Sea community – examined with mesocosm experiments’

Spatial variations in CO2 fluxes in the Saguenay Fjord (Quebec, Canada) and results of a water mixing model

The Saguenay Fjord is a major tributary of the St. Lawrence Estuary and is strongly stratified. A 6–8 m wedge of brackish water typically overlies up to 270 m of seawater. Relative to the St. Lawrence River, the surface waters of the Saguenay Fjord are less alkaline and host higher dissolved organic carbon (DOC) concentrations. In view of the latter, surface waters of the fjord are expected to be a net source of CO2 to the atmosphere, as they partly originate from the flushing of organic-rich soil porewaters. Nonetheless, the CO2 dynamics in the fjord are modulated with the rising tide by the intrusion, at the surface, of brackish water from the Upper St. Lawrence Estuary, as well as an overflow of mixed seawater over the shallow sill from the Lower St. Lawrence Estuary. Using geochemical and isotopic tracers, in combination with an optimization multiparameter algorithm (OMP), we determined the relative contribution of known source waters to the water column in the Saguenay Fjord, including waters that originate from the Lower St. Lawrence Estuary and replenish the fjord’s deep basins. These results, when included in a conservative mixing model and compared to field measurements, serve to identify the dominant factors, other than physical mixing, such as biological activity (photosynthesis, respiration) and gas exchange at the air–water interface, that impact the water properties (e.g., pH, pCO2) of the fjord. Results indicate that the fjord’s surface waters are a net source of CO2 to the atmosphere during periods of high freshwater discharge (e.g., spring freshet), whereas they serve as a net sink of atmospheric CO2 when their practical salinity exceeds ∼5–10.

Continue reading ‘Spatial variations in CO2 fluxes in the Saguenay Fjord (Quebec, Canada) and results of a water mixing model’

Impacts of temperature, CO2, and salinity on phytoplankton community composition in the western Arctic Ocean

The Arctic Ocean has been experiencing rapid warming, which accelerates sea ice melt. Further, the increasing area and duration of sea ice-free conditions enhance ocean uptake of CO2. We conducted two shipboard experiments in September 2015 and 2016 to examine the effects of temperature, CO2, and salinity on phytoplankton dynamics to better understand the impacts of rapid environmental changes on the Arctic ecosystem. Two temperature conditions (control: <3 and 5°C above the control), two CO2 levels (control: ∼300 and 300/450 μatm above the control; i.e., 600/750 μatm), and two salinity conditions (control: 29 in 2015 and 27 in 2016, and 1.4 below the control) conditions were fully factorially manipulated in eight treatments. Higher temperatures enhanced almost all phytoplankton traits in both experiments in terms of chl-a, accessory pigments and diatom biomass. The diatom diversity index decreased due to the replacement of chain-forming Thalassiosira spp. by solitary Cylindrotheca closterium or Pseudo-nitzschia spp. under higher temperature and lower salinity in combination. Higher CO2 levels significantly increased the growth of small-sized phytoplankton (<10 μm) in both years. Decreased salinity had marginal effects but significantly increased the growth of small-sized phytoplankton under higher CO2 levels in terms of chl-a in 2015. Our results suggest that the smaller phytoplankton tend to dominate in the shelf edge region of the Chukchi Sea in the western Arctic Ocean under multiple environmental perturbations.

Continue reading ‘Impacts of temperature, CO2, and salinity on phytoplankton community composition in the western Arctic Ocean’


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Ocean acidification in the IPCC AR5 WG II

OUP book