Posts Tagged 'nutrients'

Interactive effects of temperature, food and skeletal mineralogy mediate biological responses to ocean acidification in a widely distributed bryozoan

Marine invertebrates with skeletons made of high-magnesium calcite may be especially susceptible to ocean acidification (OA) due to the elevated solubility of this form of calcium carbonate. However, skeletal composition can vary plastically within some species, and it is largely unknown how concurrent changes in multiple oceanographic parameters will interact to affect skeletal mineralogy, growth and vulnerability to future OA. We explored these interactive effects by culturing genetic clones of the bryozoan Jellyella tuberculata (formerly Membranipora tuberculata) under factorial combinations of dissolved carbon dioxide (CO2), temperature and food concentrations. High CO2 and cold temperature induced degeneration of zooids in colonies. However, colonies still maintained high growth efficiencies under these adverse conditions, indicating a compensatory trade-off whereby colonies degenerate more zooids under stress, redirecting energy to the growth and maintenance of new zooids. Low-food concentration and elevated temperatures also had interactive effects on skeletal mineralogy, resulting in skeletal calcite with higher concentrations of magnesium, which readily dissolved under high CO2. For taxa that weakly regulate skeletal magnesium concentration, skeletal dissolution may be a more widespread phenomenon than is currently documented and is a growing concern as oceans continue to warm and acidify.

Continue reading ‘Interactive effects of temperature, food and skeletal mineralogy mediate biological responses to ocean acidification in a widely distributed bryozoan’

Interactive effects of ocean acidification and warming on growth, fitness and survival of the cold-water coral Lophelia pertusa under different food availabilities

Cold-water corals are important bioengineers that provide structural habitat for a diverse species community. About 70 % of the presently known scleractinian cold-water corals are expected to be exposed to corrosive waters by the end of this century due to ocean acidification. At the same time, the corals will experience a steady warming of their environment. Studies on the sensitivity of cold-water corals to climate change mainly concentrated on single stressors in short-term incubation approaches, thus not accounting for possible long-term acclimatisation and the interactive effects of multiple stressors. Besides, preceding studies did not test for possible compensatory effects of a change in food availability. In this study a multifactorial long-term experiment (6 months) was conducted with end-of-the-century scenarios of elevated pCO2 and temperature levels in order to examine the acclimatisation potential of the cosmopolitan cold-water coral Lophelia pertusa to future climate change related threats. For the first time multiple ocean change impacts including the role of the nutritional status were tested on L. pertusa with regard to growth, ‘fitness’, and survival. Our results show that while L. pertusa is capable of calcifying under elevated CO2 and temperature, its condition (fitness) is more strongly influenced by food availability rather than changes in seawater chemistry. Whereas growth rates increased at elevated temperature (+ 4°C), they decreased under elevated CO2 concentrations (~ 800 µatm). No difference in net growth was detected when corals were exposed to the combination of increased CO2 and temperature compared to ambient conditions. A 10-fold higher food supply stimulated growth under elevated temperature, which was not observed in the combined treatment. This indicates that increased food supply does not compensate for adverse effects of ocean acidification and underlines the importance of considering the nutritional status in studies investigating organism responses under environmental changes.

Continue reading ‘Interactive effects of ocean acidification and warming on growth, fitness and survival of the cold-water coral Lophelia pertusa under different food availabilities’

The combined effects of elevated pCO2 and food availability on Tigriopus japonicus Mori larval development, reproduction, and superoxide dismutase activity

Previous studies have shown that ocean acidification has little effect on adult Tigriopus japonicus copepods, and mainly impairs the early development and reproduction of females. This study investigated the possible interactive effect between CO2-induced seawater acidification and food availability on larval development and reproductive output in T. japonicus. Copepods were exposed to either pH 8.1 or pH 7.3 under different food concentrations (0.5 × 104–80.0 × 104 cells/mL). Both the development of nauplii and copepodites was delayed at pH 7.3 with a greater effect at lower food concentrations. The reproductive output followed a bell-shaped curve with the highest reproductive output at food concentrations between 30 × 104 and 40 × 104 cells/mL. As an indicator of oxidative stress, the activity of superoxide dismutase increased at lower pH, with a greater increase at lower food concentrations. Therefore, the effect of elevated pCO2 on T. japonicus was food dependent.

Continue reading ‘The combined effects of elevated pCO2 and food availability on Tigriopus japonicus Mori larval development, reproduction, and superoxide dismutase activity’

Effects of elevated CO2 and nitrogen supply on the growth and photosynthetic physiology of a marine cyanobacterium, Synechococcus sp. PCC7002

Ocean acidification due to increasing atmospheric CO2 concentration and coastal eutrophication are growing global threats to affect marine organisms and ecosystem health. However, little is known about their interactive impacts on marine picocyanobacteria which contribute to a large proportion of primary production. In this study, we cultivated the cyanobacterium Synechococcus sp. PCC7002 at ambient (380 ppmv) and high CO2 (1000 ppmv), across a range of nitrogen levels (LN, 10 μM NO3−; MN, 35 μM NO3−; HN, 110 μM NO3−). In LN media, elevated CO2 significantly decreased cellular chlorophyll a, but insignificantly affected growth rate, photosynthetic efficiency (Fv/Fm) and maximum relative electron transport rate (rETRmax). Nitrogen (N)-supply positively increased the growth, Fv/Fm, dissolved organic carbon (DOC) and cellular carotenoids/Chl a ratios, but decreased the rETRmax in both ambient and elevated CO2 conditions. The cellular C/N ratios were significantly increased by either elevated CO2 or N-supply, and the cell size was significantly enhanced by elevated CO2, not by N-supply. In addition, we found the N-supply alone had no significant effects on the four main components of chromophoric dissolved organic matter (cDOM) in ambient CO2, while the N-supply interacted with elevated CO2 significantly decreasing the cDOM contents in the cultures. Our results indicated that elevated CO2 and N-supply interacted to alter the physiology and cellular biochemistry of Synechococcus sp. PCC7002, providing useful information for understanding the environmental adaptability of Synechococcus to coastal ocean acidification and eutrophication.

Continue reading ‘Effects of elevated CO2 and nitrogen supply on the growth and photosynthetic physiology of a marine cyanobacterium, Synechococcus sp. PCC7002’

Nitrogen nutritional condition affects the response of energy metabolism in diatoms to elevated carbon dioxide

Marine phytoplankton are expected to benefit from enhanced carbon dioxide (CO2), attributable largely to down-regulation of the CO2 concentrating mechanism (CCM) which saves energy resources for other cellular processes. However, the nitrogen (N) nutritional condition (N-replete vs. N-limiting) of phytoplankton may affect the responses of their intracellular metabolic processes to elevated CO2. We cultured the model diatoms Thalassiosira pseudonana, Phaeodactylum tricornutum, and Thalassiosira weissflogii at ambient and elevated CO2 levels under N-replete and N-limiting conditions. Key metabolic processes, including light harvesting, C fixation, photorespiration, respiration, and N assimilation, were assessed systematically and then incorporated into an energy budget to compare the effects of CO2 on the metabolic pathways and the consequent changes in photosynthesis and C fixation as a result of energy reallocation under the different N nutritional conditions. Under the N-replete condition, down-regulation of the CCM at high CO2 was the primary contributor to increased photosynthesis rates of the diatoms. Under N-limiting conditions, elevated CO2 significantly affected the photosynthetic photon flux and respiration, in addition to CCM down-regulation and declines in photorespiration, resulting in an increase of the C:N ratio in all 3 diatom species. In T. pseudonana and T. weissflogii, the elevated C:N ratio was driven largely by an increased cellular C quota, whereas in P. tricornutum it resulted primarily from a decreased cellular N quota. The N-limited diatoms therefore could fix more C per unit of N in response to elevated CO2, which could potentially provide a negative feedback to the ongoing increase in atmospheric CO2.

Continue reading ‘Nitrogen nutritional condition affects the response of energy metabolism in diatoms to elevated carbon dioxide’

Cumulative effects of ocean acidification, eutrophication, and competition on the growth of two bloom-forming, estuarine macroalgae

While there is a growing interest in understanding how marine life will respond to future ocean acidification, many coastal ecosystems currently experience intense acidification in response to upwelling, riverine discharge, and eutrophication. Such acidification can be inhibitory to calcifying animals, but less is known regarding how non-calcifying macro algae may respond to elevated CO2. Additionally, while the ability of some marine autotrophs to benefit from elevated CO2 over others may result in shifts in community structure, such shifts can also be affected by competition between primary producers. In order to examine what role ocean acidification, eutrophication, and competition plays in the growth of marine macroalgae, a series of experiments were performed during summer through fall 2014 and 2015 with North Atlantic populations of Gracilaria tikvahiae and Ulva rigida that were grown in situ within a mesotrophic estuary (Shinnecock Bay, NY, USA) or exposed to normal and elevated, but environmentally realistic, levels of pCO2 and/or nutrients (nitrogen and phosphorus), as well as being subjected to competition with each other as well as with diatom and dinoflagellate assemblages (2015). Across the 2014 and 2015 experiments, the growth rates of Gracilaria were significantly increased by 70% (2014) and 34% (2015) when exposed to elevated levels of pCO2 (p<0.05). Under the same conditions, the growth rates of Ulva were increased by 30% (2014) and 41% (2015). For nearly all 2014 experiments, Gracilaria was unaffected by nutrient enrichment. In contrast, the growth response of Ulva was more complex as this alga experienced significantly (p<0.05) increased growth rates in response to both elevated pCO2 and nutrients and, in two cases, pCO2 and nutrients interacted to provide synergistically enhanced growth. For the 2015 experiments, growth rates of Gracilaria with or without elevated pCO2 were unaffected by the presence of competing plankton or Ulva. In contrast, growth of Ulva was significantly reduced when grown with Gracilaria (p<0.05) and in several experiments, growth rates of Ulva were found to be significantly reduced when competing with plankton (p<0.05). Dinoflagellates grew significantly faster when exposed to elevated pCO2 (p<0.05) but experienced significantly reduced growth rates grown with Gracilaria (p<0.05). Across all experiments, Gracilaria and Ulva experienced significant declines in tissue δ13C signatures, suggesting that increased growth rates were associated with a shift from use of HCO3- to CO2 use. This shift in carbon use coupled with significantly increased growth in response to elevated pCO2 suggests that photosynthesis of these algae was limited by their inorganic carbon supply. For the 2015 experiments, elevated C:N ratios among macroalgae suggested that competition for N also shaped interactions among autotrophs, particularly for Ulva. Collectively, these study demonstrates that while several types of estuarine autotrophs can benefit from elevated pCO2 levels, their relative benefit can change when direct competition with other primary producers is considered with Gracilaria outcompeting Ulva and dinoflagellates outcompeting diatoms under high pCO2.

Continue reading ‘Cumulative effects of ocean acidification, eutrophication, and competition on the growth of two bloom-forming, estuarine macroalgae’

Influence of ocean acidification and deep water upwelling on oligotrophic plankton communities in the subtropical North Atlantic: Insights from an in situ mesocosm study

Oceanic uptake of anthropogenic carbon dioxide (CO2) causes pronounced shifts in marine carbonate chemistry and a decrease in seawater pH. Increasing evidence indicates that these changes – summarized by the term ocean acidification (OA) – can significantly affect marine food webs and biogeochemical cycles. However, current scientific knowledge is largely based on laboratory experiments with single species and artificial boundary conditions, whereas studies of natural plankton communities are still relatively rare. Moreover, the few existing community-level studies were mostly conducted in rather eutrophic environments, while less attention has been paid to oligotrophic systems such as the subtropical ocean gyres.

Here we report from a recent in situ mesocosm experiment off the coast of Gran Canaria in the eastern subtropical North Atlantic, where we investigated the influence of OA on the ecology and biogeochemistry of plankton communities in oligotrophic waters under close-to-natural conditions. This paper is the first in this Research Topic of Frontiers in Marine Biogeochemistry and provides (1) a detailed overview of the experimental design and important events during our mesocosm campaign, and (2) first insights into the ecological responses of plankton communities to simulated OA over the course of the 62-day experiment.

One particular scientific objective of our mesocosm experiment was to investigate how OA impacts might differ between oligotrophic conditions and phases of high biological productivity, which regularly occur in response to upwelling of nutrient-rich deep water in the study region. Therefore, we specifically developed a deep water collection system that allowed us to obtain ~85 m3 of seawater from ~650 m depth. Thereby, we replaced ~20% of each mesocosm’s volume with deep water, and thus successfully simulated a deep water upwelling event that induced a pronounced plankton bloom.

Our study revealed significant effects of OA on the entire food web, leading to a restructuring of plankton communities that emerged during the oligotrophic phase, and was further amplified during the bloom that developed in response to deep water addition. Such CO2-related shifts in plankton community composition could have consequences for ecosystem productivity, biomass transfer to higher trophic levels, and biogeochemical element cycling of oligotrophic ocean regions.

Continue reading ‘Influence of ocean acidification and deep water upwelling on oligotrophic plankton communities in the subtropical North Atlantic: Insights from an in situ mesocosm study’


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Ocean acidification in the IPCC AR5 WG II

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