Posts Tagged 'nutrients'



Nitrogen enrichment offsets direct negative effects of ocean acidification on a reef-building crustose coralline alga

Ocean acidification (OA) and nutrient enrichment threaten the persistence of near shore ecosystems, yet little is known about their combined effects on marine organisms. Here, we show that a threefold increase in nitrogen concentrations, simulating enrichment due to coastal eutrophication or consumer excretions, offset the direct negative effects of near-future OA on calcification and photophysiology of the reef-building crustose coralline alga, Porolithon onkodes. Projected near-future pCO2 levels (approx. 850 µatm) decreased calcification by 30% relative to ambient conditions. Conversely, nitrogen enrichment (nitrate + nitrite and ammonium) increased calcification by 90–130% in ambient and high pCO2 treatments, respectively. pCO2 and nitrogen enrichment interactively affected instantaneous photophysiology, with highest relative electron transport rates under high pCO2 and high nitrogen. Nitrogen enrichment alone increased concentrations of the photosynthetic pigments chlorophyll a, phycocyanin and phycoerythrin by approximately 80–450%, regardless of pCO2. These results demonstrate that nutrient enrichment can mediate direct organismal responses to OA. In natural systems, however, such direct benefits may be counteracted by simultaneous increases in negative indirect effects, such as heightened competition. Experiments exploring the effects of multiple stressors are increasingly becoming important for improving our ability to understand the ramifications of local and global change stressors in near shore ecosystems.

Continue reading ‘Nitrogen enrichment offsets direct negative effects of ocean acidification on a reef-building crustose coralline alga’

High CO2 under nutrient fertilization increases primary production and biomass in subtropical phytoplankton communities: a mesocosm approach

The subtropical oceans are home to one of the largest ecosystems on Earth, contributing to nearly one third of global oceanic primary production. Ocean warming leads to enhanced stratification in the oligotrophic ocean but also intensification in cross-shore wind gradients and thus in eddy kinetic energy across eastern boundary regions of the subtropical gyres. Phytoplankton thriving in a future warmer oligotrophic subtropical ocean with enhanced COlevels could therefore be patchily fertilized by increased mesoscale and submesoscale variability inducing nutrient pumping into the surface ocean. Under this premise, we have tested the response of three size classes (0.2–2, 2–20, and >20 μm) of subtropical phytoplankton communities in terms of primary production, chlorophyll and cell biomass, to increasing COconcentrations and nutrient fertilization during an in situ mesocosm experiment in oligotrophic waters off of the island of Gran Canaria. We found no significant CO2-related effect on primary production and biomass under oligotrophic conditions (phase I). In contrast, primary production, chlorophyll and biomass displayed a significant and pronounced increase under elevated CO2 conditions in all groups after nutrient fertilization, both during the bloom (phase II) and post-bloom (phase III) conditions. Although the relative increase of primary production in picophytoplankton (250%) was 2.5 higher than in microphytoplankton (100%) after nutrient fertilization, comparing the high and low CO2 treatments, microphytoplankton dominated in terms of biomass, contributing >57% to the total. These results contrast with similar studies conducted in temperate and cold waters, where consistently small phytoplankton benefitted after nutrient additions at high CO2, pointing to different CO2-sensitivities across plankton communities and ecosystem types in the ocean.

Continue reading ‘High CO2 under nutrient fertilization increases primary production and biomass in subtropical phytoplankton communities: a mesocosm approach’

Interactive effect of nitrogen source and high CO2 concentration on the growth of the dinoflagellate Alexandrium tamarense and its toxicity to zebrafish (Danio rerio) embryos

Highlights

•The growth of A. tamarense was influenced more strongly by CO2 than by N sources.
•The toxicity of A. tamarense was influenced more strongly by the N than by CO2.
•The toxicity of A. tamarense associated with the cell density was best fitted using a logistic function.
•Zebrafish embryo had the detoxication systems to avoid the damage of A. tamarense.

Abstract

The effects and interactive effects of different nitrogen (N) sources (ammonium, nitrate, and urea) and carbon dioxide (CO2) concentrations were investigated on Alexandrium tamarense, a harmful marine dinoflagellate, by measuring its growth (μ), extracellular carbonic anhydrase (CA), and its toxicity to zebrafish (Danio rerio) embryo. The μ and CA were influenced more strongly by CO2 concentrations rather than by N sources; significant effects of CO2 on μ and CA were observed under low CO2 concentration (LC) conditions compared to high CO2 concentration (HC) conditions. The ammonium and nitrate media under LC conditions had the maximum μ and CA, which was inhibited under HC conditions. The embryotoxic effects were influenced more strongly by the N sources than by CO2 concentrations, thus excluding the lower deformation in urea under HC conditions. Moreover, the antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GPX), glutathione S-transferase (GST), and catalase (CAT) were detected in normal (untreated) zebrafish embryos, and among them, the level of SOD was the highest. In summary, this study provides a clear insight for understanding the effects and interactive effects of N sources and CO2 concentrations on the growth and toxicity of harmful dinoflagellates.

Continue reading ‘Interactive effect of nitrogen source and high CO2 concentration on the growth of the dinoflagellate Alexandrium tamarense and its toxicity to zebrafish (Danio rerio) embryos’

Ocean acidification and nutrient limitation synergistically reduce growth and photosynthetic performances of a green tide alga Ulva linza (update)

Large-scale green tides have been invading the coastal zones of the western Yellow Sea annually since 2008. Meanwhile, oceans are becoming more acidic due to continuous absorption of anthropogenic carbon dioxide, and intensive seaweed cultivation in Chinese coastal areas is leading to severe regional nutrient limitation. However, little is known about the combined effects of global and local stressors on the eco-physiology of bloom-forming algae. We cultured Ulva linza for 9–16 days under two levels of pCO2 (400 and 1000 µatm) and four treatments of nutrients (nutrient repletion, N limitation, P limitation, and N–P limitation) to investigate the physiological responses of this green tide alga to the combination of ocean acidification and nutrient limitation. For both sporelings and adult plants, elevated pCO2 did not affect the growth rate when cultured under nutrient-replete conditions but reduced it under P limitation; N or P limitations by themselves reduced growth rate. P limitation resulted in a larger inhibition in growth for sporelings compared to adult plants. Sporelings under P limitation did not reach the mature stage after 16 days of culture while those under P repletion became mature by day 11. Elevated pCO2 reduced net photosynthetic rate for all nutrient treatments but increased nitrate reductase activity and soluble protein content under P-replete conditions. N or P limitation reduced nitrate reductase activity and soluble protein content. These findings indicate that ocean acidification and nutrient limitation would synergistically reduce the growth of Ulva species and may thus hinder the occurrence of green tides in a future ocean environment.

Continue reading ‘Ocean acidification and nutrient limitation synergistically reduce growth and photosynthetic performances of a green tide alga Ulva linza (update)’

Responses of the large centric diatom Coscinodiscus sp. to interactions between warming, elevated CO2, and nitrate availability

Marine ecosystems are facing multiple anthropogenic global changes, including ocean acidification, warming, and reduced nutrient supplies. Together, these will challenge phytoplankton including large centric diatoms such as Coscinodiscus sp., a group that is important to ocean food webs and carbon export. We investigated the interactive effects of warming, elevated CO2, and nitrate availability on Coscinodiscus growth, elemental stoichiometry, and Fe and C uptake rates in a four‐treatment factorial experiment combining two CO2 levels (∼400 ppm and 800 ppm) and two temperatures (16°C and 20°C) across seven nitrate concentrations (1–100 μmol L−1). Higher temperatures led to higher maximum growth rates (μmax), but also higher half‐saturation constants for nitrate (K1/2), while elevated CO2 increased K1/2 only at the warmer temperature. Lower μmax/K1/2 ratios under warming and rising CO2 indicated a higher nitrate requirement at these conditions. High temperature decreased cellular P and Si contents and consequently increased N : P and C : Si ratios, especially at ambient CO2. Fe : C uptake ratios responded positively to lower nitrate levels, lower CO2, and warming. Significant interactions between nitrate availability and temperature or CO2 were observed for specific growth rates, chlorophyll a and Si contents, Fe : C, N : P, and Si : C, while temperature and CO2 interactions were only significant for μmax/K1/2 and cellular P content. The mutual interactions among CO2 concentrations, temperature, and nitrate supply may all affect future growth, physiology, and carbon export by Coscinodiscus sp., however, in general warming and nitrate availability appear to be more influential than CO2.

Continue reading ‘Responses of the large centric diatom Coscinodiscus sp. to interactions between warming, elevated CO2, and nitrate availability’

Nutrient pollution disrupts key ecosystem functions on coral reefs

There is a long history of examining the impacts of nutrient pollution and pH on coral reefs. However, little is known about how these two stressors interact and influence coral reef ecosystem functioning. Using a six-week nutrient addition experiment, we measured the impact of elevated nitrate (NO−3) and phosphate (PO3−4) on net community calcification (NCC) and net community production (NCP) rates of individual taxa and combined reef communities. Our study had four major outcomes: (i) NCC rates declined in response to nutrient addition in all substrate types, (ii) the mixed community switched from net calcification to net dissolution under medium and high nutrient conditions, (iii) nutrients augmented pH variability through modified photosynthesis and respiration rates, and (iv) nutrients disrupted the relationship between NCC and aragonite saturation state documented in ambient conditions. These results indicate that the negative effect of NO−3 and PO3−4 addition on reef calcification is likely both a direct physiological response to nutrients and also an indirect response to a shifting pH environment from altered NCP rates. Here, we show that nutrient pollution could make reefs more vulnerable to global changes associated with ocean acidification and accelerate the predicted shift from net accretion to net erosion.

Continue reading ‘Nutrient pollution disrupts key ecosystem functions on coral reefs’

The interactive effects of ocean acidification, food availability, and source location on the growth and physiology of the California mussel

Research shows ocean acidification (OA) can have largely negative impacts on marine organisms and ecosystems. Prior laboratory studies show that shelled marine invertebrates (e.g., molluscs) exhibit reduced growth rates and weaker shells when experiencing OA-related stress. However, populations of the critical intertidal mussel species, Mytilus californianus, which experience naturally acidic water due to upwelling in certain parts of Northern California have been observed to have relatively stronger and thicker shells and higher growth rates than those that experience less frequent exposure to upwelling. To address the discrepancies between negative effects of OA exposure in the laboratory and seemingly positive effects off OA exposure in the field we collected juvenile mussels from four separate locations on the northern California coast that vary in exposure to upwelling-driven OA and raised them under ambient, constantly acidified, or intermittently acidified seawater conditions. Half of the mussels in each of the experimental treatments were given access to either ambient or elevated food concentrations. Although higher food availability increased shell and overall mussel growth, variation in mussel life-history traits among locations appears to be driven primarily by inherent differences (i.e. genetics or epigenetics). In particular, overall growth, soft tissue mass, and shell dissolution in mussels were associated with source-specific upwelling strength while adductor muscle mass along with shell growth and strength of mussels were associated with source-specific levels of predation risk. Oxygen consumption of mussels did not significantly vary among food, pH or source location treatments, suggesting that differences in growth rates were not due to differences in differences in metabolic or energetic efficiencies between individuals. Although not statistically significant, mussels from areas of high crab predation risk tended to survive crab attacks in the lab better than mussels from other areas. My data suggests that the adaptive potential of M. californianus to respond to future OA conditions is dependent on local environmental factors such as upwelling strength, food availability, and predation risk. My study addresses a significant gap in our understanding of the mechanism behind conflicting observations of increased growth in the field associated with low pH and previous laboratory results, demonstrating the importance of environmental context in shaping the organismal response to current and future OA conditions.

Continue reading ‘The interactive effects of ocean acidification, food availability, and source location on the growth and physiology of the California mussel’


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