Posts Tagged 'algae'

Future climate change scenarios differentially affect three abundant algal species in southwestern Australia

Three species of macroalgae (Ecklonia radiata, Sargassum linearifolium, and Laurencia brongniartii) were subjected to future climate change conditions, tested directly for changes in their physiology and chemical ecology, and used in feeding assays with local herbivores to identify the indirect effects of climatic stressors on subsequent levels of herbivory. Each alga had distinct physical and chemical responses to the changes in environmental conditions. In high temperature conditions, S. linearifolium exhibited high levels of bleaching and low maximum quantum yield. For E. radiata, the alga became more palatable to herbivores and the C:N ratios were either higher or lower, dependent on the treatment. Laurencia brongniartii was effected in all manipulations when compared to controls, with increases in bleaching, blade density, and C:N ratios and decreases in growth, maximum quantum yield, blade toughness, total phenolics and consumption by mesograzers. The differential responses we observed in each species have important implications for benthic communities in projected climate change conditions and we suggest that future studies target multi-species assemblage responses.

Continue reading ‘Future climate change scenarios differentially affect three abundant algal species in southwestern Australia’

Ocean acidification and kelp development: Reduced pH has no negative effects on meiospore germination and gametophyte development of Macrocystis pyrifera and Undaria pinnatifida

The absorption of anthropogenic CO2 by the oceans is causing a reduction in the pH of the surface waters termed ocean acidification (OA). This could have substantial effects on marine coastal environments where fleshy (non-calcareous) macroalgae are dominant primary producers and ecosystem engineers. Few OA studies have focused on the early life stages of large macroalgae such as kelps. This study evaluated the effects of seawater pH on the ontogenic development of meiospores of the native kelp Macrocystis pyrifera and the invasive kelp Undaria pinnatifida, in south-eastern New Zealand. Meiospores of both kelps were released into four seawater pH treatments (pHT 7.20, extreme OA predicted for 2300; pHT 7.65, OA predicted for 2100; pHT 8.01, ambient pH; and pHT 8.40, pre-industrial pH) and cultured for 15 d. Meiospore germination, germling growth rate, and gametophyte size and sex ratio were monitored and measured. Exposure to reduced pHT (7.20 and 7.65) had positive effects on germling growth rate and gametophyte size in both M. pyrifera and U. pinnatifida, whereas, higher pHT (8.01 and 8.40) reduced the gametophyte size in both kelps. Sex ratio of gametophytes of both kelps was biased towards females under all pHT treatments, except for U. pinnatifida at pHT 7.65. Germling growth rate under OA was significantly higher in M. pyrifera compared to U. pinnatifida but gametophyte development was equal for both kelps under all seawater pHT treatments, indicating that the microscopic stages of the native M. pyrifera and the invasive U. pinnatifida will respond similarly to OA.

Continue reading ‘Ocean acidification and kelp development: Reduced pH has no negative effects on meiospore germination and gametophyte development of Macrocystis pyrifera and Undaria pinnatifida’

Physiological response of a golden tide alga (Sargassum muticum) to the interaction of ocean acidification and phosphorus enrichment (update)

The development of golden tides is potentially influenced by global change factors, such as ocean acidification and eutrophication, but related studies are very scarce. In this study, we cultured a golden tide alga, Sargasssum muticum, at two levels of pCO2 (400 and 1000 µatm) and phosphate (0.5 and 40 µM) to investigate the interactive effects of elevated pCO2 and phosphate on the physiological properties of the thalli. Higher pCO2 and phosphate (P) levels alone increased the relative growth rate by 41 and 48 %, the net photosynthetic rate by 46 and 55 %, and the soluble carbohydrates by 33 and 62 %, respectively, while the combination of these two levels did not promote growth or soluble carbohydrates further. The higher levels of pCO2 and P alone also enhanced the nitrate uptake rate by 68 and 36 %, the nitrate reductase activity (NRA) by 89 and 39 %, and the soluble protein by 19 and 15 %, respectively. The nitrate uptake rate and soluble protein was further enhanced, although the nitrate reductase activity was reduced when the higher levels of pCO2 and P worked together. The higher pCO2 and higher P levels alone did not affect the dark respiration rate of the thalli, but together they increased it by 32 % compared to the condition of lower pCO2 and lower P. The neutral effect of the higher levels of pCO2 and higher P on growth and soluble carbohydrates, combined with the promoting effect on soluble protein and dark respiration, suggests that more energy was drawn from carbon assimilation to nitrogen assimilation under conditions of higher pCO2 and higher P; this is most likely to act against the higher pCO2 that caused acid–base perturbation via synthesizing H+ transport-related protein. Our results indicate that ocean acidification and eutrophication may not boost golden tide events synergistically, although each one has a promoting effect.

Continue reading ‘Physiological response of a golden tide alga (Sargassum muticum) to the interaction of ocean acidification and phosphorus enrichment (update)’

Effects of ocean acidification on the potency of macroalgal allelopathy to a common coral

Many coral reefs have phase shifted from coral to macroalgal dominance. Ocean acidification (OA) due to elevated CO2 is hypothesised to advantage macroalgae over corals, contributing to these shifts, but the mechanisms affecting coral-macroalgal interactions under OA are unknown. Here, we show that (i) three common macroalgae are more damaging to a common coral when they compete under CO2 concentrations predicted to occur in 2050 and 2100 than under present-day conditions, (ii) that two macroalgae damage corals via allelopathy, and (iii) that one macroalga is allelopathic under conditions of elevated CO2, but not at ambient levels. Lipid-soluble, surface extracts from the macroalga Canistrocarpus (=Dictyota) cervicornis were significantly more damaging to the coral Acropora intermedia growing in the field if these extracts were from thalli grown under elevated vs ambient concentrations of CO2. Extracts from the macroalgae Chlorodesmis fastigiata and Amansia glomerata were not more potent when grown under elevated CO2. Our results demonstrate increasing OA advantages seaweeds over corals, that algal allelopathy can mediate coral-algal interactions, and that OA may enhance the allelopathy of some macroalgae. Other mechanisms also affect coral-macroalgal interactions under OA, and OA further suppresses the resilience of coral reefs suffering blooms of macroalgae.

Continue reading ‘Effects of ocean acidification on the potency of macroalgal allelopathy to a common coral’

Kelp and carbon: pathways and barriers to acquisition and transport

Large brown algae in the class Phaeophyceae (Heterokontophyta) form the structural and energetic foundation of temperate and subtropical nearshore marine forests of high productivity and ecological diversity. This dissertation examines the carbon uptake and transport physiology of large brown algae with a particular focus on the plastic or adaptive responses of these physiological traits to their abiotic environment. Chapter 1 takes an anatomical and modeling approach to investigate the structure and function of photosynthate transport networks (analogous to phloem) in diverse members of the Laminariales. To evaluate the existence of scaling and optimization of the kelp vascular system, a model of optimized transport anatomy was developed and tested with a  diverse suite of kelp species in the Laminariales. Results revealed a surprising lack of universal scaling in the kelps and the presence of optimized transport anatomy in the giant kelp (Macrocystis pyrifera) only. Chapter 2 focuses on the dynamics of carbon uptake in M. pyrifera, which can acquire both carbon dioxide and bicarbonate as carbon substrates for photosynthesis. To evaluate whether the proportion of carbon dioxide and bicarbonate utilized by M. pyrifera is constant or a variable function of their fluctuating environment, oxygen evolution experiments were carried out  n entire blades from several targeted populations in the Monterey Bay. Results indicated that M. pyrifera possesses a plastic carbon uptake physiology in which proportionally more bicarbonate is used in high irradiance and high flow conditions, but that local populations have not yet developed fixed genetic differences. Chapter 3 investigates the mechanism and patterns of carbon stable isotope discrimination in M. pyrifera. Results of a dual field and laboratory incubation approach indicate that 13C discrimination patterns are determined by a complex interaction of light intensity, dissolved inorganic carbon limitation, and fractionation occurring during transport of polysaccharides. Overall, this dissertation informs patterns and mechanisms of carbon uptake and transport in kelps, and highlights the many ways in which kelps may impact and structure their ecosystems.

Continue reading ‘Kelp and carbon: pathways and barriers to acquisition and transport’

How ocean acidification can benefit calcifiers

Reduction in seawater pH due to rising levels of anthropogenic carbon dioxide (CO2) in the world’s oceans is a major force set to shape the future of marine ecosystems and the ecological services they provide 1 and 2. In particular, ocean acidification is predicted to have a detrimental effect on the physiology of calcifying organisms [3]. Yet, the indirect effects of ocean acidification on calcifying organisms, which may counter or exacerbate direct effects, is uncertain. Using volcanic CO2 vents, we tested the indirect effects of ocean acidification on a calcifying herbivore (gastropod) within the natural complexity of an ecological system. Contrary to predictions, the abundance of this calcifier was greater at vent sites (with near-future CO2 levels). Furthermore, translocation experiments demonstrated that ocean acidification did not drive increases in gastropod abundance directly, but indirectly as a function of increased habitat and food (algal biomass). We conclude that the effect of ocean acidification on algae (primary producers) can have a strong, indirect positive influence on the abundance of some calcifying herbivores, which can overwhelm any direct negative effects. This finding points to the need to understand ecological processes that buffer the negative effects of environmental change.

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Molecular response of Sargassum vulgare to acidification at volcanic CO2 vents – insights from de novo transcriptomic analysis

Ocean acidification is an emerging problem that is expected to impact ocean species to varying degrees. Currently, little is known about its effect on molecular mechanisms induced in fleshy macroalgae. To elucidate genome wide responses to acidification, a comparative transcriptome analysis was carried out between Sargassum vulgare populations growing under acidified conditions at volcanic CO2 vents and a control site. Several transcripts involved in a wide range of cellular and metabolic processes were differentially expressed. No drastic changes were observed in the carbon acquisition processes and RuBisCO level. Moreover, relatively few stress genes, including those for antioxidant enzymes and heat shock proteins, were affected. Instead, increased expression of transcripts involved in energy metabolism, photosynthetic processes, and ion homeostasis suggested that algae increased energy production to maintain ion-homeostasis and other cellular processes. Also, an increased allocation of carbon to cell wall and carbon storage was observed. A number of genes encoding proteins involved in cellular signaling, information storage and processing, and transposition were differentially expressed between the two conditions. The transcriptional changes of key enzymes were largely confirmed by enzymatic activity measurements. Altogether, the changes induced by acidification indicate an adaptation of growth and development of S. vulgare at the volcanic CO2 vents, suggesting that this fleshy alga exhibits a high plasticity to low pH and can adopt molecular strategies to grow also in future more acidified waters.

Continue reading ‘Molecular response of Sargassum vulgare to acidification at volcanic CO2 vents – insights from de novo transcriptomic analysis’


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