Posts Tagged 'nutrients'

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’

Interactive effects of CO2, temperature, irradiance, and nutrient limitation on the growth and physiology of the marine diatom Thalassiosira pseudonana (Coscinodiscophyceae)

The marine diatom Thalassiosira pseudonana was grown in continuous culture systems to study the interactive effects of temperature, irradiance, nutrient limitation, and the partial pressure of CO2 (pCO2) on its growth and physiological characteristics. The cells were able to grow at all combinations of low and high irradiance (50 and 300 μmol photons · m−2 · s−1, respectively, of visible light), low and high pCO2 (400 and 1,000 μatm, respectively), nutrient limitation (nitrate‐limited and nutrient‐replete conditions), and temperatures of 10–32°C. Under nutrient‐replete conditions, there was no adverse effect of high pCO2 on growth rates at temperatures of 10–25°C. The response of the cells to high pCO2 was similar at low and high irradiance. At supraoptimal temperatures of 30°C or higher, high pCO2 depressed growth rates at both low and high irradiance. Under nitrate‐limited conditions, cells were grown at 38 ± 2.4% of their nutrient‐saturated rates at the same temperature, irradiance, and pCO2. Dark respiration rates consistently removed a higher percentage of production under nitrate‐limited versus nutrient‐replete conditions. The percentages of production lost to dark respiration were positively correlated with temperature under nitrate‐limited conditions, but there was no analogous correlation under nutrient‐replete conditions. The results suggest that warmer temperatures and associated more intense thermal stratification of ocean surface waters could lower net photosynthetic rates if the stratification leads to a reduction in the relative growth rates of marine phytoplankton, and at truly supraoptimal temperatures there would likely be a synergistic interaction between the stresses from temperature and high pCO2 (lower pH).

Continue reading ‘Interactive effects of CO2, temperature, irradiance, and nutrient limitation on the growth and physiology of the marine diatom Thalassiosira pseudonana (Coscinodiscophyceae)’

Hypoxia and acidification, individually and in combination, disrupt herbivory and reduce survivorship of the gastropod, Lacuna vincta

Acidification and deoxygenation are two consequences of climate change that also co-occur in eutrophied coastal zones and can have deleterious effects on marine life. While the effects of hypoxia on marine herbivores have been well-studied, how ocean acidification combined with hypoxia affects herbivory is poorly understood. This study examined how herbivory and survival by the gastropod Lacuna vincta grazing on the macroalgae Ulva rigida was influenced by hypoxia and ocean acidification, alone and in combination, with and without food limitation. Experiments exposed L. vincta to a range of environmentally realistic dissolved oxygen (0.7 – 8 mg L–1) and pH (7.3 – 8.0 total scale) conditions for 3 – 72 h, with and without a starvation period and quantified herbivory and survival. While acidified conditions (pH < 7.4) reduced herbivory when combined with food limitation, low oxygen conditions (< 4 mg L–1) reduced herbivory and survival regardless of food supply. When L. vincta were starved and grazed in acidified conditions herbivory was additively reduced, whereas starvation and hypoxia synergistically reduced grazing rates. Overall, low oxygen had a more inhibitory effect on herbivory than low pH. Shorter exposure times (9, 6, and 3 h) were required to reduce grazing at lower DO levels (∼2.4, ∼1.6, and ∼0.7 mg L–1, respectively). Herbivory ceased entirely following a three-hour exposure to DO of 0.7 mg L–1 suggesting that episodes of diurnal hypoxia disrupt grazing by these gastropods. The suppression of herbivory in response to acidified and hypoxic conditions could create a positive feedback loop that promotes ‘green tides’ whereby reduced grazing facilitates the overgrowth of macroalgae that cause nocturnal acidification and hypoxia, further disrupting herbivory and promoting the growth of macroalgae. Such feedback loops could have broad implications for estuarine ecosystems where L. vincta is a dominant macroalgal grazer and will intensify as climate change accelerates.

Continue reading ‘Hypoxia and acidification, individually and in combination, disrupt herbivory and reduce survivorship of the gastropod, Lacuna vincta’

Effects of multiple drivers of ocean global change on the physiology and functional gene expression of the coccolithophore Emiliania huxleyi

Ongoing ocean global change due to anthropogenic activities is causing multiple chemical and physical seawater properties to change simultaneously, which may affect the physiology of marine phytoplankton. The coccolithophore Emiliania huxleyi is a model species often employed in the study of the marine carbon cycle. The effect of ocean acidification (OA) on coccolithophore calcification has been extensively studied; however, physiological responses to multiple environmental drivers are still largely unknown. Here we examined two‐way and multiple driver effects of OA and other key environmental drivers—nitrate, phosphate, irradiance, and temperature—on the growth, photosynthetic, and calcification rates, and the elemental composition of E. huxleyi. In addition, changes in functional gene expression were examined to understand the molecular mechanisms underpinning the physiological responses. The single driver manipulation experiments suggest decreased nitrate supply being the most important driver regulating E. huxleyi physiology, by significantly reducing the growth, photosynthetic, and calcification rates. In addition, the interaction of OA and decreased nitrate supply (projected for year 2100) had more negative synergistic effects on E. huxleyi physiology than all other two‐way factorial manipulations, suggesting a linkage between the single dominant driver (nitrate) effects and interactive effects with other drivers. Simultaneous manipulation of all five environmental drivers to the conditions of the projected year 2100 had the largest negative effects on most of the physiological metrics. Furthermore, functional genes associated with inorganic carbon acquisition (RubisCO, AEL1, and δCA) and calcification (CAX3, AEL1, PATP, and NhaA2) were most downregulated by the multiple driver manipulation, revealing linkages between responses of functional gene expression and associated physiological metrics. These findings together indicate that for more holistic projections of coccolithophore responses to future ocean global change, it is necessary to understand the relative importance of environmental drivers both individually (i.e., mechanistic understanding) and interactively (i.e., cumulative effect) on coccolithophore physiology.

Continue reading ‘Effects of multiple drivers of ocean global change on the physiology and functional gene expression of the coccolithophore Emiliania huxleyi’

Vulnerability of global coral reef habitat suitability to ocean warming, acidification and eutrophication

Coral reefs are threatened by global and local stressors. Yet, reefs appear to respond differently to different environmental stressors. Using a global dataset of coral reef occurrence as a proxy for the long‐term adaptation of corals to environmental conditions in combination with global environmental data, we show here how global (warming: sea surface temperature; acidification: aragonite saturation state, Ωarag) and local (eutrophication: nitrate concentration, and phosphate concentration) stressors influence coral reef habitat suitability. We analyse the relative distance of coral communities to their regional environmental optima. In addition, we calculate the expected change of coral reef habitat suitability across the tropics in relation to an increase of 0.1°C in temperature, an increase of 0.02 μmol/L in nitrate, an increase of 0.01 μmol/L in phosphate and a decrease of 0.04 in Ωarag. Our findings reveal that only 6% of the reefs worldwide will be unaffected by local and global stressors and can thus act as temporary refugia. Local stressors, driven by nutrient increase, will affect 22% of the reefs worldwide, whereas global stressors will affect 11% of these reefs. The remaining 61% of the reefs will be simultaneously affected by local and global stressors. Appropriate wastewater treatments can mitigate local eutrophication and could increase areas of temporary refugia to 28%, allowing us to ‘buy time’, while international agreements are found to abate global stressors.

Continue reading ‘Vulnerability of global coral reef habitat suitability to ocean warming, acidification and eutrophication’

Nutrient availability modulates the effects of climate change on growth and photosynthesis of marine macroalga Pyropia haitanensis (Bangiales, Rhodophyta)

The present research investigated the effect of pCO2 levels (C), seawater temperature (T), and nutrient availability (N) on the growth and physiochemical changes in Pyropia haitanensis. With nutrient enrichment, the interaction of higher pCO2 increased relative growth rates (RGR) by 105.9% when temperature increased (22 °C) compared with the control (lower T, lower C, and lower N: LTLCLN). The higher pCO2 decreased the Pm rates at the lower temperature (18 °C), yet displayed no interaction with higher T or N levels. The higher N increased dark respiration rate (Rd) at 18 °C. At 22 °C, higher pCO2 significantly enhanced the maximum ratio of (quantum yields (Fv/Fo) and the maximum quantum yield (ψpo), while it sharply decreased the absorption of photons per active reaction center (ABS/RC) and dissipation of energy fluxes (per RC) (DIo/RC). Higher temperature obviously reduced the Fv/Fo and ψpo under ambient CO2 level. The higher pCO2 significantly increased the phycoerythrin (PE) and phycocyanin (PC) contents, while higher temperature decreased the PE contents with elevated CO2 and declined the PC content regardless of CO2 condition. At lower nutrient condition, higher pCO2 increased Chl a content. Soluble carbohydrates (SC) and soluble protein (SP) content almost was unchanged among all treatments. Our findings indicate that nutrient availability may regulate photosynthetic mechanism to offset the negative effect of future ocean warming on P. haitanensis, thereby sustaining or increasing the biomass yield of the algae.

Continue reading ‘Nutrient availability modulates the effects of climate change on growth and photosynthesis of marine macroalga Pyropia haitanensis (Bangiales, Rhodophyta)’

High CO2 concentration and iron availability determine the metabolic inventory in an Emiliania huxleyi‐dominated phytoplankton community

Ocean acidification (OA), a consequence of anthropogenic carbon dioxide (CO2) emissions, strongly impacts marine ecosystems. OA also influences iron (Fe) solubility, affecting biogeochemical and ecological processes. We investigated the interactive effects of CO2 and Fe availability on the metabolome response of a natural phytoplankton community. Using mesocosms we exposed phytoplankton to ambient (390 μatm) or future CO2 levels predicted for the year 2100 (900 μatm), combined with ambient (4.5 nM) or high (12 nM) dissolved iron (dFe). By integrating over the whole phytoplankton community, we assigned functional changes based on altered metabolite concentrations. Our study revealed the complexity of phytoplankton metabolism. Metabolic profiles showed three stages in response to treatments and phytoplankton dynamics. Metabolome changes were related to the plankton group contributing respective metabolites, explaining bloom decline and community succession. CO2 and Fe affected metabolic profiles. Most saccharides, fatty acids, amino acids, and many sterols significantly correlated with the high dFe treatment at ambient p CO2. High CO2 lowered the abundance of many metabolites irrespective of Fe. However, sugar alcohols accumulated, indicating potential stress. We demonstrate that not only altered species composition, but also changes in the metabolic landscape affecting the plankton community, may change as a consequence of future high‐CO2 oceans.

Continue reading ‘High CO2 concentration and iron availability determine the metabolic inventory in an Emiliania huxleyi‐dominated phytoplankton community’

Cuttlefish buoyancy in response to food availability and ocean acidification

Carbon dioxide concentration in the atmosphere is expected to continue rising by 2100, leading to a decrease in ocean pH in a process known as ocean acidification (OA). OA can have a direct impact on calcifying organisms, including on the cuttlebone of the common cuttlefish Sepia officinalis. Moreover, nutritional status has also been shown to affect the cuttlebone structure and potentially affect buoyancy. Here, we aimed to understand the combined effects of OA (980 μatm CO2) and food availability (fed vs. non-fed) on the buoyancy of cuttlefish newborns and respective cuttlebone weight/area ratio (as a proxy for calcification). Our results indicate that while OA elicited negative effects on hatching success, it did not negatively affect the cuttlebone weight/area ratio of the hatchlings—OA led to an increase in cuttlebone weight/area ratio of fed newborns (but not in unfed individuals). The proportion of “floating” (linked to buoyancy control loss) newborns was greatest under starvation, regardless of the CO2 treatment, and was associated with a drop in cuttlebone weight/area ratio. Besides showing that cuttlefish buoyancy is unequivocally affected by starvation, here, we also highlight the importance of nutritional condition to assess calcifying organisms’ responses to ocean acidification.

Continue reading ‘Cuttlefish buoyancy in response to food availability and ocean acidification’

Reduced growth with increased quotas of particulate organic and inorganic carbon in the coccolithophore Emiliania huxleyi under future ocean climate change conditions

Effects of ocean acidification and warming on marine primary producers can be modulated by other environmental factors, such as levels of nutrients and light. Here, we investigated the interactive effects of five oceanic environmental drivers (CO2, temperature, light, dissolved inorganic nitrogen and phosphate) on growth rate, particulate organic (POC) and inorganic (PIC) carbon quotas of the cosmopolitan coccolithophore Emiliania huxleyi. Population growth rate increased with increasing temperature (16 to 20 °C) and light intensities (60 to 240 μmol photons m−2  s−1), but decreased with elevated pCO2 concentrations (370 to 960 μatm) and reduced availability of nitrate (24.3 to 7.8 μmol L−1) and phosphate (1.5 to 0.5 μmol L−1). POC quotas were predominantly enhanced by combined effects of increased pCO2 and decreased availability of phosphate. PIC quotas increased with decreased availability of nitrate and phosphate. Our results show that concurrent changes in nutrient concentrations and pCO2 levels predominantly affected growth, photosynthetic carbon fixation and calcification of E. huxleyi, and imply that plastic responses to progressive ocean acidification, warming and decreasing availability of nitrate and phosphate reduce population growth rate while increasing cellular quotas of particulate organic and inorganic carbon of E. huxleyi, ultimately affecting coccolithophore-related ecological and biogeochemical processes.

Continue reading ‘Reduced growth with increased quotas of particulate organic and inorganic carbon in the coccolithophore Emiliania huxleyi under future ocean climate change conditions’


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