Posts Tagged 'nutrients'

Springtime spatial distributions of biogenic sulfur compounds in the Yangtze river estuary and their responses to seawater acidification and dust

The spatial distributions of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethylsulfoxide (DMSO) were investigated in the Yangtze River Estuary from 9 to 23 March, 2018. The average concentrations of DMS, dissolved DMSP (DMSPd), particulate DMSP (DMSPp), dissolved DMSO (DMSOd) and particulate DMSO (DMSOp) were 3.00 ± 2.53, 1.75 ± 1.08, 10.89 ± 14.28, 9.80 ± 7.79, and 9.51 ± 8.90 nmol L‐1, respectively. The high DMS and DMSP concentrations occurred mainly in the open sea, exhibiting distribution patterns similar to chlorophyll a (Chl‐a). Due to the release of resuspended sediments, elevated DMSO concentrations were observed in the bottom waters of some stations. The three sulfur compounds were positively correlated with Chl‐a (p < 0.05), suggesting that phytoplankton played an essential role in the production of sulfur compounds. Comparisons with previous research showed that the concentrations of DMS, DMSP, and DMSOp exhibited clear seasonal variability. The average sea‐to‐air flux of DMS was 8.19 ± 12.94 μmol m‐2 d‐1 in the study area, indicating that the estuary and continental shelf sea were significant contributors to the global sulfur cycle. Ship‐based incubation experiments showed that lower pH inhibited the production of the three biogenic sulfur compounds, while the addition of dust promoted their release. Therefore, in the future, the inhibitory effect of seawater acidification on the production of phytoplankton and sulfur compounds might be offset, to some degree, by the input of nutrient‐rich dust.

Continue reading ‘Springtime spatial distributions of biogenic sulfur compounds in the Yangtze river estuary and their responses to seawater acidification and dust’

The dual benefit of ocean acidification for the laminarialean kelp, Saccharina latissima: enhanced growth and reduced herbivory

The laminarialean kelp, Saccharina latissima, is a common macroalgae along rocky shorelines that is also frequently used in aquaculture. This study examined how ocean acidification may alter the growth of S. latissima as well as grazing on S. latissima by the gastropod, Lacuna vincta. Under elevated nutrients, S. latissima experienced significantly enhanced growth at pCO2 levels >1,200 µatm compared to ambient pCO2 (~400 µatm). Elevated pCO2 (>830 µatm) also significantly reduced herbivory of L. vincta grazing on S. latissima relative to ambient pCO2. There was no difference in grazing of S. latissima previously grown under elevated or ambient pCO2, suggesting lowered herbivory was due to harm to the gastropods rather than alteration of the biochemical composition of the kelp. Decreased herbivory was specifically elicited when L. vincta were exposed to elevated pCO2 in the absence of food for >18 h prior to grazing, with reduced grazing persisting 72 h. Elevated growth of S. latissima and reduced grazing by L. vincta at 1,200 µatm pCO2 combined to increase net growth rates of S. latissima by more than four-fold relative to ambient pCO2L. vincta consumed 70% of daily production by S. latissima under ambient pCO2 but only 38% and 9% at 800 µatm and 1,200 µatm, respectively. Collectively, decreased grazing by L. vincta coupled with enhanced growth of S. latissima under elevated pCO2 demonstrates that increased CO2 associated with climate change and/or coastal processes will dually benefit commercially and ecologically important kelps by both promoting growth and reducing grazing pressure. 

Continue reading ‘The dual benefit of ocean acidification for the laminarialean kelp, Saccharina latissima: enhanced growth and reduced herbivory’

Photosynthesis and calcification of the coccolithophore Emiliania huxleyi are more sensitive to changed levels of light and CO2 under nutrient limitation

Highlights

  • Nutrient limitation reduced the light intensity for cells to achieve the highest rates of photosynthesis and calcification.
  • Nitrate limitation enhanced calcification rate and phosphate limitation reduced photosynthetic rate.
  • Electron transport rate linearly and positively correlated with rates of photosynthesis and calcification.

Abstract

Photophysiological responses of phytoplankton to changing multiple environmental drivers are essential in understanding and predicting ecological consequences of ocean climate changes. In this study, we investigated the combined effects of two CO2 levels (410 and 925 μatm) and five light intensities (80 to 480 μmol photons m−2 s−1) on cellular pigments contents, photosynthesis and calcification of the coccolithophore Emiliania huxleyi grown under nutrient replete and limited conditions, respectively. Our results showed that high light intensity, high CO2 level and nitrate limitation acted synergistically to reduce cellular chlorophyll a and carotenoid contents. Nitrate limitation predominantly enhanced calcification rate; phosphate limitation predominantly reduced photosynthetic carbon fixation rate, with larger extent of the reduction under higher levels of CO2 and light. Reduced availability of both nitrate and phosphate under the elevated CO2 concentration decreased saturating light levels for the cells to achieve the maximal relative electron transport rate (rETRmax). Light-saturating levels for rETRmax were lower than that for photosynthetic and calcification rates under the nutrient limitation. Regardless of the culture conditions, rETR under growth light levels correlated linearly and positively with measured photosynthetic and calcification rates. Our findings imply that E. huxleyi cells acclimated to macro-nutrient limitation and elevated CO2 concentration decreased their light requirement to achieve the maximal electron transport, photosynthetic and calcification rates, indicating a photophysiological strategy to cope with CO2 rise/pH drop in shoaled upper mixing layer above the thermocline where the microalgal cells are exposed to increased levels of light and decreased levels of nutrients.

Continue reading ‘Photosynthesis and calcification of the coccolithophore Emiliania huxleyi are more sensitive to changed levels of light and CO2 under nutrient limitation’

Phosphorus enrichment masked the negative effects of ocean acidification on picophytoplankton and photosynthetic performance in the oligotrophic Indian Ocean

Highlights

  • High pCO2 and P interactively increased the abundances of Syn, Pro and PEuks.
  • Rising pCO2 alone decreased the abundances of Syn, Pro and PEuks.
  • Elevated pCO2 alone facilitated the NPQNSV process significantly.
  • There was a strong coupling of picophytoplankton and the charge separation rates.
  • P enrichment masked the negative effects of OA on picophytoplankton and photosynthesis.

Abstract

Dynamics of picophytoplankton and photosynthesis will be inevitably impacted by changing marine environment, such as ocean acidification and nutrient supply, but related studies are very scarce. Here we cultured the picophytoplankton-dominated surface water of the oligotrophic Eastern Indian Ocean (EIO; R/V Shiyan-3, 20 March to 18 May 2019) at two levels of pCO2 (400 and 1000 ppm) and phosphate (0.05 and 1.50 µM) to investigate the interactive effects of elevated pCO2 and phosphate (P) on the dynamics of picophytoplankton and photosynthetic properties. High pCO2 and P levels interactively increased the abundances of SynechococcusProchlorococcus and picoeukaryotes by 33%, 18%, and 21%, respectively, of which high P level had a major promoting effect. Conversely, rising pCO2 alone decreased their abundances by 9%, 32%, and 46%, respectively. For the photophysiological responses in relation to the combination of high pCO2 and P levels, there was an increase in the maximum (Fv/Fm) and effective (Fq‘/Fm‘) photochemical efficiency, the electron transfer rates (ETRRCII) and the charge separation rates (JVPSII, an indicator of primary production), but a decrease in the non-photochemical quenching (NPQNSV). Elevated pCO2 alone facilitated the NPQNSV process significantly, ultimately leading to reduced light use efficiency (e.g., Fv/Fm, Fq‘/Fm‘ and ETRRCII) and primary production (JVPSII). There was a strong coupling of picophytoplankton and JVPSII, suggesting the EIO primary productivity was potentially controlled by picophytoplankton. Overall, our results indicate that the negative effects caused by ocean acidification may be masked or outweighted by the role that P availability plays in regulating growth and metabolism in this oligotrophic ecosystem.

Continue reading ‘Phosphorus enrichment masked the negative effects of ocean acidification on picophytoplankton and photosynthetic performance in the oligotrophic Indian Ocean’

Coastal ocean acidification and nitrogen loading facilitate invasions of the non-indigenous red macroalga, Dasysiphonia japonica

Coastal ecosystems are prone to multiple anthropogenic and natural stressors including eutrophication, acidification, and invasive species. While the growth of some macroalgae can be promoted by excessive nutrient loading and/or elevated pCO2, responses differ among species and ecosystems. Native to the western Pacific Ocean, the filamentous, turf-forming rhodophyte, Dasysiphonia japonica, appeared in estuaries of the northeastern Atlantic Ocean during the 1980s and the northwestern Atlantic Ocean during the late 2000s. Here, we report on the southernmost expansion of the D. japonica in North America and the effects of elevated nutrients and elevated pCO2 on the growth of D. japonica over an annual cycle in Long Island, New York, USA. Growth limitation of the macroalga varied seasonally. During winter and spring, when water temperatures were < 15 °C, growth was significantly enhanced by elevated pCO2 (p < 0.05). During summer and fall, when the water temperature was 15–24 °C, growth was significantly higher under elevated nutrient treatments (p < 0.05). When temperatures reached 28 °C, the macroalga grew poorly and was unaffected by nutrients or pCO2. The δ13C content of regional populations of D. japonica was −30‰, indicating the macroalga is an obligate CO2-user. This result, coupled with significantly increased growth under elevated pCO2 when temperatures were < 15 °C, indicates this macroalga is carbon-limited during colder months, when in situ pCO2 was significantly lower in Long Island estuaries compared to warmer months when estuaries are enriched in metabolically derived CO2. The δ15N content of this macroalga (9‰) indicated it utilized wastewater-derived N and its N limitation during warmer months coincided with lower concentrations of dissolved inorganic N in the water column. Given the stimulatory effect of nutrients on this macroalga and that eutrophication can promote seasonally elevated pCO2, this study suggests that eutrophic estuaries subject to peak annual temperatures < 28 °C may be particularly vulnerable to future invasions of D. japonica as ocean acidification intensifies. Conversely, nutrient reductions would serve as a management approach that would make coastal regions more resilient to invasions by this macroalga.

Continue reading ‘Coastal ocean acidification and nitrogen loading facilitate invasions of the non-indigenous red macroalga, Dasysiphonia japonica’

Windows of vulnerability: seasonal mismatches in exposure and resource identity determine ocean acidification’s effect on a primary consumer at high latitude

It is well understood that differences in the cues used by consumers and their resources in fluctuating environments can give rise to trophic mismatches governing the emergent effects of global change. Trophic mismatches caused by changes in consumer energetics during periods of low resource availability have received far less attention, although this may be common for consumers during winter when primary producers are limited by light. Even less is understood about these dynamics in marine ecosystems, where consumers must cope with energetically costly changes in CO2‐driven carbonate chemistry that will be most pronounced in cold temperatures. This may be especially important for calcified marine herbivores, such as the pinto abalone (Haliotis kamschatkana). H. kamschatkana are of high management concern in the North Pacific due to the active recreational fishery and their importance among traditional cultures, and research suggests they may require more energy to maintain their calcified shells and acid/base balance with ocean acidification. Here we use field surveys to demonstrate seasonal mismatches in the exposure of marine consumers to low pH and algal resource identity during winter in a subpolar, marine ecosystem. We then use these data to test how the effects of exposure to seasonally relevant pH conditions on H. kamschatkana are mediated by seasonal resource identity. We find that exposure to projected future winter pH conditions decreases metabolism and growth, and this effect on growth is pronounced when their diet is limited to the algal species available during winter. Our results suggest that increases in the energetic demands of pinto abalone caused by ocean acidification during winter will be exacerbated by seasonal shifts in their resources. These findings have profound implications for other marine consumers and highlight the importance of considering fluctuations in exposure and resources when inferring the emergent effects of global change.

Continue reading ‘Windows of vulnerability: seasonal mismatches in exposure and resource identity determine ocean acidification’s effect on a primary consumer at high latitude’

Ocean-related global change alters lipid biomarker production in common marine phytoplankton (update)

Lipids, in their function as trophic markers in food webs and organic matter source indicators in the water column and sediments, provide a tool for reconstructing the complexity of global change effects on aquatic ecosystems. It remains unclear how ongoing changes in multiple environmental drivers affect the production of key lipid biomarkers in marine phytoplankton. Here, we tested the responses of sterols, alkenones and fatty acids (FAs) in the diatom Phaeodactylum tricornutum, the cryptophyte Rhodomonas sp. and the haptophyte Emiliania huxleyi under a full-factorial combination of three temperatures (12, 18 and 24 C), three N : P supply ratios (molar ratios 10 : 1, 24 : 1 and 63 : 1) and two pCO2 levels (560 and 2400 µatm) in semicontinuous culturing experiments. Overall, N and P deficiency had a stronger effect on per-cell contents of sterols, alkenones and FAs than warming and enhanced pCO2. Specifically, P deficiency caused an overall increase in biomarker production in most cases, while N deficiency, warming and high pCO2 caused nonsystematic changes. Under future ocean scenarios, we predict an overall decrease in carbon-normalized contents of sterols and polyunsaturated fatty acids (PUFAs) in E. huxleyi and P. tricornutum and a decrease in sterols but an increase in PUFAs in Rhodomonas sp. Variable contents of lipid biomarkers indicate a diverse carbon allocation between marine phytoplankton species in response to changing environments. Thus, it is necessary to consider the changes in key lipids and their consequences for food-web dynamics and biogeochemical cycles, when predicting the influence of global change on marine ecosystems.

Continue reading ‘Ocean-related global change alters lipid biomarker production in common marine phytoplankton (update)’

Ocean acidification and short‐term organic matter enrichment alter coral reef sediment metabolism through different pathways

Ocean acidification (OA) and organic matter (OM) enrichment (due to coastal eutrophication) could act in concert to shift coral reef carbonate sediments from a present state of net calcification to a future state of net dissolution, but no studies have examined the combined effect of these stressors on sediment metabolism and dissolution. This study used 22‐hour incubations in flume aquaria with captive sediment communities to measure the combined effect of elevated pCO2 (representing Ocean Acidification) and particulate organic carbon (representing coastal eutrophication) on coral reef sediment gross primary productivity (GPP), respiration (R), and net calcification (Gnet). Relative to control sediment communities, both OA (pCO2 ~ 1000 μatm) and OM enrichment (~ + 40 μmol C L‐1) significantly decreased rates of sediment Gnet by 1.16 and 0.18 mmol CaCO3 m‐2 h‐1, respectively, but the mechanism behind this decrease differed. The OA‐mediated transition to net dissolution was physiochemical, as rates of GPP and R remained unaffected and dissolution was solely enhanced by a decline in the aragonite saturation state (Ωarg) of the overlying water column and the physical factors governing the porewater exchange rate with this overlying water column. In contrast, the OM‐mediated decline in Gnet was due to a decline in the overlying seawater Ωarg due to the increased respiratory addition of CO2. The decrease in Gnet in response to a combination of both stressors was additive (‐ 0.09 mmol CaCO3 m‐2 h‐1 relative to OA alone) but this decrease did not significantly differ from the individual effect of either stressor. In this study OA was the primary driver of future carbonate sediment dissolution, but longer‐term experiments with chronic organic matter enrichment are required.

Continue reading ‘Ocean acidification and short‐term organic matter enrichment alter coral reef sediment metabolism through different pathways’

Meta-analysis of multiple driver effects on marine phytoplankton highlights modulating role of pCO2

Responses of marine primary production to a changing climate are determined by a concert of multiple environmental changes, for example in temperature, light, pCO2, nutrients, and grazing. To make robust projections of future global marine primary production, it is crucial to understand multiple driver effects on phytoplankton. This meta-analysis quantifies individual and interactive effects of dual driver combinations on marine phytoplankton growth rates. Almost 50% of the single-species laboratory studies were excluded because central data and metadata (growth rates, carbonate system, experimental treatments) were insufficiently reported. The remaining data (42 studies) allowed for the analysis of interactions of pCO2 with temperature, light, and nutrients, respectively. Growth rates mostly respond non-additively, whereby the interaction with increased pCO2 profusely dampens growth-enhancing effects of high temperature and high light. Multiple and single driver effects on coccolithophores differ from other phytoplankton groups, especially in their high sensitivity to increasing pCO2. Polar species decrease their growth rate in response to high pCO2, while temperate and tropical species benefit under these conditions. Based on the observed interactions and projected changes, we anticipate primary productivity to: (a) first increase but eventually decrease in the Arctic Ocean once nutrient limitation outweighs the benefits of higher light availability; (b) decrease in the tropics and mid-latitudes due to intensifying nutrient limitation, possibly amplified by elevated pCO2; and (c) increase in the Southern Ocean in view of higher nutrient availability and synergistic interaction with increasing pCO2. Growth-enhancing effect of high light and warming to coccolithophores, mainly Emiliania huxleyi, might increase their relative abundance as long as not offset by acidification. Dinoflagellates are expected to increase their relative abundance due to their positive growth response to increasing pCO2 and light levels. Our analysis reveals gaps in the knowledge on multiple driver responses and provides recommendations for future work on phytoplankton.

Continue reading ‘Meta-analysis of multiple driver effects on marine phytoplankton highlights modulating role of pCO2’

Short-term effects of increased CO2, nitrate and temperature on photosynthetic activity in Ulva rigida (Chlorophyta) estimated by different pulse amplitude modulated fluorometers and oxygen evolution

Short-term effects of pCO2 (700 – 380 ppm; HC-LC) and nitrate content (50-5 βM; HN-LC) on photosynthesis, estimated by different pulse amplitude modulated (PAMs) fluorometers and by oxygen evolution, were investigated in Ulva rigida (Chlorophyta) under solar radiation (ex-situ) and in the laboratory under artificial light (in-situ). After 6-days of incubation at ambient temperature (AT), algae were subjected to a 4 oC-temperature increase (AT+4oC) for 3 d. Both in-situ and ex-situ, maximal electron transport rate (ETRmax) and in situ gross photosynthesis (GP) measured by O2 evolution presented the highest values under HCHN, and the lowest under HCLN, across all measuring systems. Maximal quantum yield (Fv/Fm), and ETRmax of PSII (ETR(II)max) and of PSI (ETR(I)max), decreased under HCLN under AT+4°C. Ex situ ETR was higher than in situ ETR. At noon, Fv/Fm decreased (indicating photoinhibition), whereas ETR(II)max and maximal non-photochemical quenching (NPQmax) increased. ETR(II)max decreased under AT+4oC in contrast to Fv/Fm, photosynthetic efficiency (αETR) and saturated irradiance (EK). Thus, U. rigida exhibited a decrease in photosynthetic production under acidification, LN levels and AT+4oC. These results emphasize the importance of studying the interactive effects between environmental parameters using in-situ vs. ex-situ conditions when aiming to evaluate the impact of global change on marine macroalgae.

Continue reading ‘Short-term effects of increased CO2, nitrate and temperature on photosynthetic activity in Ulva rigida (Chlorophyta) estimated by different pulse amplitude modulated fluorometers and oxygen evolution’


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