Posts Tagged 'growth'

Effects of ocean acidification and eutrophication on the macroalgae Ulva spp.

Ocean acidification is the increased absorption of atmospheric CO2 in seawater and the consequent decrease in pH. This phenomenon is occurring throughout the global oceans while land use changes and large human populations near coasts are linked to increased nutrient concentrations in seawater. Ulva spp. blooms caused by nutrient enrichment occur regularly in some parts of the world and are known as green tides. There is concern that ocean acidification may increase green tides and intensify ecological and economic damages. Ulva spp. can utilize bicarbonate (HCO3-) as an inorganic carbon source, but this comes at an energetic cost as HCO3- must be converted to CO2 before it can be used for carbon fixation. Therefore, increased utilization of pCO2 with ocean acidification may benefit Ulva spp. Ocean acidification and eutrophication will occur simultaneously in many coastal ecosystems. The goal of the following investigations was to determine the effects of ocean acidification and nutrient enrichment alone and their interaction on photosynthetic, nutrient, and growth physiology of Ulva spp. In Chapter 2, the response of Ulva australis to pHT and ammonium (NH4+) enrichment were investigated in a seven day growth experiment using a range of pHT (7.56 – 7.84) and ambient and enriched NH4+ concentrations. I measured relative growth rates (RGRs), NH4+ uptake rates and pools, photosynthetic characteristics, and tissue carbon and nitrogen content. There was no interaction of pHT and NH4+ enrichment on the physiological parameters. The RGR was not affected by pHT, but was an average of two times higher in the enriched NH4+ treatment. rETRmax, total chlorophyll, and tissue nitrogen increased with both NH4+ enrichment and decreased pHT. The C:N ratio decreased with decreasing pH and with NH4+ enrichment. Although rETRmax increased and the C:N ratio decreased under decreased pH, these metabolic changes did not translate to higher growth rates. The results show that U. australis growth and physiology is more sensitive to NH4+ than it is to pH and that there is no interactive effect of NH4+ enrichment and decreasing pH. In Chapter 3, Ulva lactuca was grown for 22 days under a range of pCO2 and NH4+ concentrations and a multiple linear regression was used to analyze RGRs, NH4+ and NO3- pools, in situ NH4+ and NO3- uptake rates, tissue carbon and nitrogen content, carbohydrate and protein concentrations, and photosynthesis irradiance curves (P-I curves). The results from model selection and model-averaging techniques allowed me to make predictive models across a range of relevant ocean acidification and eutrophication scenarios and measure the effect sizes of pCO2, NH4+ enrichment, and their interaction. Overall, there was no effect of pCO2 and NH4+ on RGRs after day 5. However, there was a synergistic effect of pCO2 and NH4+ enrichment on the growth rates during days 0 – 5. When pCO2 and NH4+ concentrations increased simultaneously, NO3- uptake rates increased, which may have contributed to increased growth as seen in days 0 – 5. Maximum photosynthetic rates (Pmax) decreased with increasing pCO2 and there was a positive interaction of pCO2 and NH4+ on indicating CCMs were altered under these conditions. This shows that under high light intensities, Pmax was negatively affected by pCO2 and CCMs are not altered when nutrients are limited. Ultimately, there was no longer-term effect of ocean acidification and eutrophication on Ulva lactuca growth. Nutrient enrichment is a major cause of green tide blooms around the world and Ulva australis had the ability to enhance nutrient, photosynthetic, and growth physiology with NH4+ enrichment. Conversely, Ulva lactuca collected from a eutrophic environment, did not respond to NH4+ in terms of growth. Both chapters provided evidence that ocean acidification is unlikely to affect the growth rates of Ulva spp. However, the exception was a positive interactive effect of pCO2 and NH4+ enrichment on the growth rate of U. lactuca during the first five days, suggesting ocean acidification could play a role in initiating Ulva spp. blooms in a eutrophic environment. This could be an important consideration for determining how green tides will be affected by ocean acidification in coastal areas where nutrient enrichment occurs in pulses, resulting in transiently increased nitrogen concentrations.

Continue reading ‘Effects of ocean acidification and eutrophication on the macroalgae Ulva spp.’

Effect of ocean acidification and elevated temperature on growth of calcifying tubeworm shells (Spirorbis spirorbis): an in-situ benthocosm approach

The calcareous tubeworm Spirorbis spirorbis is a wide-spread serpulid species in the Baltic Sea, where it commonly grows as an epibiont on brown macroalgae (genus Fucus). It lives within a Mg-calcite shell and could be affected by ocean acidification and temperature rise induced by the predicted future atmospheric CO2 increase. However, Spirorbis tubes grow in a chemically modified boundary layer around the algae, which may mitigate acidification. In order to investigate how increasing temperature and rising pCO2 may influence S. spirorbis shell growth we carried out four seasonal experiments in the ‘Kiel Outdoor Benthocosms’ at elevated pCO2 and temperature conditions. Compared to laboratory batch culture experiments the benthocosm approach provides a better representation of natural conditions for physical and biological ecosystem parameters, including seasonal variations. We find that growth rates of S. spirorbis are significantly controlled by ontogenetic and seasonal effects. The length of the newly grown tube is inversely related to the initial diameter of the shell. Our study showed no significant difference of the growth rates between ambient atmospheric and elevated (1100 ppm) pCO2 conditions. No influence of daily average CaCO3 saturation state on the growth rates of S. spirorbiswas observed. We found, however, net growth of the shells even in temporarily undersaturated bulk solutions, under conditions that concurrently favored selective shell surface dissolution. The results suggest an overall resistance of S. spirorbis growth to acidification levels predicted for the year 2100 in the Baltic Sea. In contrast, S. spirorbis did not survive at mean seasonal temperatures exceeding 24 °C during the summer experiments. In the autumn experiments at ambient pCO2, the growth rates of juvenile S. spirorbis were higher under elevated temperature conditions. The results reveal that S. spirorbis may prefer moderately warmer conditions during their early life stages but will suffer from an excessive temperature increase and from increasing shell corrosion as a consequence of progressing ocean acidification.
Continue reading ‘Effect of ocean acidification and elevated temperature on growth of calcifying tubeworm shells (Spirorbis spirorbis): an in-situ benthocosm approach’

Physiological and biochemical responses of Emiliania huxleyi to ocean acidification and warming are modulated by UV radiation

Marine phytoplankton such as bloom-forming, calcite-producing coccolithophores, are naturally exposed to solar UV radiation (UVR, 280–400 nm) in the ocean’s upper mixed layers. Nevertheless, effects of increasing CO2-induced ocean acidification and warming have rarely been investigated in the presence of UVR. We examined calcification and photosynthetic carbon fixation performance in the most cosmopolitan coccolithophorid, Emiliania huxleyi, grown under high (1000 μatm, HC; pHT: 7.70) and low (400 μatm, LC; pHT: 8.02) CO2levels, at 15 °C (LT), 20 °C (MT) and 24 °C (HT) with or without UVR. The HC treatment didn’t affect photosynthetic carbon fixation at 15 °C, but significantly enhanced it with increasing temperature. Exposure to UVR inhibited photosynthesis, with higher inhibition by UVA (320–395 nm) than UVB (295–320 nm), except in the HC and 24 °C-grown cells, in which UVB caused more inhibition than UVA. Reduced thickness of the coccolith layer in the HC-grown cells appeared to be responsible for the UV-induced inhibition, and an increased repair rate of UVA-derived damage in the HCHT-grown cells could be responsible for lowered UVA-induced inhibition. While calcification was reduced with the elevated CO2 concentration, exposure to UVB or UVA affected it differentially, with the former inhibiting and the latter enhancing it. UVA-induced stimulation of calcification was higher in the HC-grown cells at 15 and 20 °C, whereas at 24 °C, observed enhancement was not significant. The calcification to photosynthesis ratio (Cal / Pho ratio) was lower in the HC treatment, and increasing temperature also lowered the value. However, at 20 and 24 °C, exposures to UVR significantly increased the Cal / Pho ratio, especially in HC-grown cells, by up to 100 %. This implies that UVR can counteract the negative effects of the greenhouse treatment on the Cal / Pho ratio, and so may be a key stressor when considering the impacts of future greenhouse conditions on E. huxleyi.

Continue reading ‘Physiological and biochemical responses of Emiliania huxleyi to ocean acidification and warming are modulated by UV radiation’

Solar UVR sensitivity of phyto- and bacterioplankton communities from Patagonian coastal waters under increased nutrients and acidification

The effects of ultraviolet radiation (UVR) under future expected conditions of acidification and increase in nutrient inputs were studied on a post-bloom phytoplankton and bacterioplankton community of Patagonian coastal waters. We performed an experiment using microcosms where two environmental conditions were mimicked using a cluster approach: present (ambient nutrients and pH) and future (increased nutrients and acidification), and acclimating the samples for five days to two radiation treatments (full solar radiation [+UVR] and exclusion of UVR [–UVR]). We evaluated the short-term (hours) sensitivity of the community to solar UVR through chlorophyll afluorescence parameters (e.g. the effective photochemical quantum yield of PSII [ΦPSII]) at the beginning, at the mid-point and at the end of the acclimation period. Primary production and heterotrophic bacterial production (HBP) were determined, and biological weighting functions were calculated, at the beginning and at the end of the acclimation period. Mid-term effects (days) were evaluated as changes in taxonomic composition, growth rates and size structure of the community. Although the UVR-induced inhibition on ΦPSII decreased in both clusters, samples remained sensitive to UVR after the 5 days of acclimation. Also, under the future conditions, there was, in general, an increase in the phytoplankton carbon incorporation rates along the experiment as compared to the present conditions. Bacterioplankton sensitivity to UVR changed along the experiment from inhibition to enhancement of HBP, and future environmental conditions stimulated bacterial growth, probably due to indirect effects caused by phytoplankton. Those changes in the microbial loop functioning and structure under future global change conditions might have important consequences for the carbon pump and thus for the carbon sequestration and trophodynamics of Patagonian coastal waters.

Continue reading ‘Solar UVR sensitivity of phyto- and bacterioplankton communities from Patagonian coastal waters under increased nutrients and acidification’

Combined effects of elevated pCO2 and warming facilitate Cyanophage infections

Elevated pCO2 and warming are generally expected to influence cyanobacterial growth, and may promote the formation of blooms. Yet, both climate change factors may also influence cyanobacterial mortality by favoring pathogens, such as viruses, which will depend on the ability of the host to adapt. To test this hypothesis, we grew Plectonema boryanum IU597 under two temperature (25 and 29°C) and two pCO2 (400 and 800 μatm) conditions for 1 year, after which all treatments were re-exposed to control conditions for a period of 3 weeks. At several time points during the 1 year period, and upon re-exposure, we measured various infection characteristics of it associated cyanophage PP, including the burst size, latent period, lytic cycle and the efficiency of plaquing (EOP). As expected, elevated pCO2 promoted growth of P. boryanumequally over the 1 year period, but warming did not. Burst size increased in the warm treatment, but decreased in both the elevated pCO2 and combined treatment. The latent period and lytic cycle both became shorter in the elevated pCO2 and higher temperature treatment, and were further reduced by the combined effect of both factors. Efficiency of plaquing (EOP) decreased in the elevated pCO2 treatment, increased in the warm treatment, and increased even stronger in the combined treatment. These findings indicate that elevated pCO2 enhanced the effect of warming, thereby further promoting the virus infection rate. The re-exposure experiments demonstrate adaptation of the host leading to higher biomass build-up with elevated pCO2 over the experimental period, and lower performance upon re-exposure to control conditions. Similarly, virus burst size and EOP increased when given warm adapted host, but were lower as compared to the control when the host was re-exposed to control conditions. Our results demonstrate that adaptation but particularly physiological acclimation to climate change conditions favored viral infections, while limited host plasticity and slow adaptation after re-exposure to control conditions impeded host biomass build-up and viral infections.

Continue reading ‘Combined effects of elevated pCO2 and warming facilitate Cyanophage infections’

Short-term growth and biomechanical responses of the temperate seagrass Cymodocea nodosa to CO2 enrichment

Seagrasses are often regarded as climate change ‘winners’ because they exhibit higher rates of photosynthesis, carbon fixation and growth when exposed to increasing levels of ocean acidification. However, questions remain whether such growth enhancement compromises the biomechanical properties of the plants, altering their vulnerability to structural damage and leaf loss. Here, we investigated the short-term (6 wk) effects of decreasing pH by CO2 enrichment on the growth, morphology and leaf-breaking force of the temperate seagrass Cymodocea nodosa. We found that the plant biomass balance under levels of acidification representative of short-term climate change projections (pH 8.04) was positive and led to an increase in leaf abundance in the shoots. However, we also found that plant biomass balance was negative under levels of acidification experienced presently (pH 8.29) and those projected over the long-term (pH 7.82). Leaf morphology (mean leaf length, thickness and width) was invariant across our imposed acidification gradient, although leaves were slightly stronger under [CO2] representative of short-term climate change. Taken together, these findings indicate that a subtle increase in growth and mechanical resistance of C. nodosa is likely to occur following short- to medium-term changes in ocean chemistry, but that these positive effects are unlikely to be maintained over the longer term. Our study emphasises the need to account for the interdependencies between environmental conditions and variations in multiple aspects of the structure and functioning of seagrass communities when considering the likely consequences of climate change.

Continue reading ‘Short-term growth and biomechanical responses of the temperate seagrass Cymodocea nodosa to CO2 enrichment’

Indirect effects of ocean acidification drive feeding and growth of juvenile crown-of-thorns starfish, Acanthaster planci

The indirect effects of changing climate in modulating trophic interactions can be as important as the direct effects of climate stressors on consumers. The success of the herbivorous juvenile stage of the crown-of-thorns starfish (COTS), Acanthaster planci, may be affected by the impacts of ocean conditions on its crustose coralline algal (CCA) food. To partition the direct effects of near future ocean acidification on juvenile COTS and indirect effects through changes in their CCA food, COTS were grown in three pHT levels (7.9, 7.8, 7.6) and fed CCA grown at similar pH levels. Consumption of CCA by COTS was bolstered when the COTS were grown in low pH and when they were fed CCA grown in low pH regardless of the pH in which the COTS were reared. COTS fed CCA grown at pH 7.6 grew fastest, but the pH/pCO2 that the COTS were reared in had no direct effect on growth. Ocean acidification conditions decreased the C : N ratio and carbonate levels in the CCA. Bolstered growth in COTS may be driven by enhanced palatability, increased nutritive state and reduced defences of their CCA food. These results indicate that near future acidification will increase the success of early juvenile COTS and boost recruitment into the coral-eating life stage.

Continue reading ‘Indirect effects of ocean acidification drive feeding and growth of juvenile crown-of-thorns starfish, Acanthaster planci’

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Ocean acidification in the IPCC AR5 WG II

OUP book