A novel in situ system to evaluate the effect of high CO2 on photosynthesis and biochemistry of seaweeds (original) (raw)
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Algal Research, 2020
Although negative responses of tropical calcifying organisms to ocean acidification have been widely reported, the modulating potential of irradiance combined with elevated pCO 2 has not been well studied. In this study, the interactive effects of elevated pCO 2 and irradiance availability on the physiology of calcifying macroalgae Halimeda cylindracea and Halimeda lacunalis were investigated using a fully factorial, 28-day aquaria coupling experiment. The results of the present study demonstrate that elevated pCO 2 negatively influences growth, photosynthesis, calcification and other physiological processes of both Halimeda species. However, these negative effects could be mitigated to some extent by increased irradiance availability. Specific growth rate (SGR), net calcification rates (G net) and maximum quantum yield (F v /F m) decreased significantly by 6.84%-86.70%, 51.78%-62.29% and 2.37%-28.91% in elevated pCO 2 treatments. However, SGR, G net and F v /F m increased by 3.39%-84.78%, 29.61%-40.68% and 1.68%-6.92% in high irradiance conditions, respectively. Chl-a in elevated pCO 2 treatments was 7.75%-61.25% lower than ambient pCO 2 conditions, while the carotenoid content increased by 12.12%-57.45% in low irradiance conditions from day 20-28. Malondialdehyde (MDA) content was higher in elevated pCO 2 treatments. However, there was also a two-to four-fold increase in proline content in elevated pCO 2 treatments. Tissue total organic carbon (TC org) and nitrogen (TN) were positively correlated to CO 2 enrichment. The results of the current study suggested that elevated pCO 2 negatively influenced the physiological responses of Halimeda, while increased irradiance availability may enhance the metabolic performance in response to ocean acidification. −) and hydrogen ions (H +), which cause a decline in pH values and the saturation state (Ω) of different crystallization forms of calcium carbonate in the marine environment [3]. Gradual shifts in CO 2 , which alter the proportion and concentration of DIC, affects physiological metabolic processes, including growth, photosynthesis and calcification in a range of marine organisms [5]. These changes in seawater chemistry may have significant negative effects on calcifying organisms, as carbonate ions (CO 3 2−) in seawater are used to build their calcified skeletons and shells [9]. While OA, as a solitary factor, can induce various physiological responses, it remains difficult to ascertain the ultimate impacts of OA on marine calcifiers, with large
Variable responses of temperate calcified and fleshy macroalgae to elevated pCO2 and warming
Ices Journal of Marine Science, 2015
Anthropogenic carbon dioxide (CO 2) emissions simultaneously increase ocean temperatures and reduce ocean surface pH, a process termed ocean acidification (OA). OA is expected to negatively affect the growth and physiology of many calcified organisms, but the response of non-calcified (fleshy) organisms is less well understood. Rising temperatures and pCO 2 can enhance photosynthetic rates (within tolerance limits). Therefore, warming may interact with OA to alter biological responses of macroalgae in complicated ways. Beyond thresholds of physiological tolerance, however, rising temperatures could further exacerbate negative responses to OA. Many studies have investigated the effects of OA or warming independently of each other, but few studies have quantified the interactive effects of OA and warming on marine organisms. We conducted four short-term independent factorial CO 2 enrichment and warming experiments on six common species of calcified and fleshy macroalgae from southern California to investigate the independent and interactive effects of CO 2 and warming on growth, carbonic anhydrase (CA) enzyme activity, pigment concentrations, and photosynthetic efficiency. There was no effect of elevated pCO 2 on CA activity, pigment concentration, and photosynthetic efficiency in the macroalgal species studies. However, we found that calcareous algae suffered reduced growth rates under high pCO 2 conditions alone, although the magnitude of the effect varied by species. Fleshy algae had mixed responses of growth rates to high pCO 2 , indicating that the effects of pCO 2 enrichment are inconsistent across species. The combined effects of elevated pCO 2 and warming had a significantly negative impact on growth for both fleshy and calcareous algae; calcareous algae experienced five times more weight loss than specimens in ambient control conditions and fleshy growth was reduced by 76%. Our results demonstrate the need to study the interactive effects of multiple stressors associated with global change on marine communities.
Macroalgal responses to ocean acidification depend on nutrient and light levels
Frontiers in Marine Science, 2015
Ocean acidification may benefit algae that are able to capitalize on increased carbon availability for photosynthesis, but it is expected to have adverse effects on calcified algae through dissolution. Shifts in dominance between primary producers will have knock-on effects on marine ecosystems and will likely vary regionally, depending on factors such as irradiance (light vs. shade) and nutrient levels (oligotrophic vs. eutrophic). Thus experiments are needed to evaluate interactive effects of combined stressors in the field. In this study, we investigated the physiological responses of macroalgae near a CO 2 seep in oligotrophic waters off Vulcano (Italy). The algae were incubated in situ at 0.2 m depth using a combination of three mean CO 2 levels (500, 700-800 and 1200 μatm CO 2), two light levels (100 and 70% of surface irradiance) and two nutrient levels of N, P, and K (enriched vs. non-enriched treatments) in the non-calcified macroalga Cystoseira compressa (Phaeophyceae, Fucales) and calcified Padina pavonica (Phaeophyceae, Dictyotales). A suite of biochemical assays and in vivo chlorophyll a fluorescence parameters showed that elevated CO 2 levels benefitted both of these algae, although their responses varied depending on light and nutrient availability. In C. compressa, elevated CO 2 treatments resulted in higher carbon content and antioxidant activity in shaded conditions both with and without nutrient enrichment-they had more Chla, phenols and fucoxanthin with nutrient enrichment and higher quantum yield (F v /F m) and photosynthetic efficiency (α ETR) without nutrient enrichment. In P. pavonica, elevated CO 2 treatments had higher carbon content, F v /F m , α ETR , and Chla regardless of nutrient levels-they had higher concentrations of phenolic compounds in nutrient enriched, fully-lit conditions and more antioxidants in shaded, nutrient enriched conditions. Nitrogen content increased significantly in fertilized treatments, confirming that these algae were nutrient limited in this oligotrophic part of the Mediterranean. Our findings strengthen evidence that brown algae can be expected to proliferate as the oceans acidify where physicochemical conditions, such as nutrient levels and light, permit.
Climate change is a global phenomenon that is considered an important threat to marine ecosystems. Ocean acidification and increased seawater temperatures are among the consequences of this phenomenon. The comprehension of the effects of these alterations on marine organisms, in particular on calcified macroalgae, is still modest despite its great importance. There are evidences that macroalgae inhabiting highly variable environments are relatively resilient to such changes. Thus, the aim of this study was to evaluate experimentally the effects of CO 2-driven ocean acidification and temperature rises on the photo-synthesis of calcified macroalgae inhabiting the intertidal region, a highly variable environment. The experiments were performed in a reef mesocosm in a tropical region on the Brazilian coast, using three species of frondose calcifying macroalgae (Halimeda cuneata, Padina gymnospora, and Tricleocarpa cylindrica) and crustose coralline algae. The acidification experiment consisted of three treatments with pH levels below those occurring in the region (-0.3,-0.6,-0.9). For the temperature experiment, three temperature levels above those occurring naturally in the region (+1, +2, +4°C) were determined. The results of the acidification experiment indicate an increase on the optimum quantum yield by T. cylindrica and a decline of this parameter by coralline algae, although both only occurred at the extreme acidification treatment (-0.9). The energy dissipation mechanisms of these algae were also altered at this extreme condition. Significant effects of the temperature experiment were limited to an enhancement of the photosynthetic performance by H. cuneata although only at a modest temperature increase (+1°C). In general, the results indicate a possible photosynthetic adaptation and/or acclimation of the studied macroalgae to the expected future ocean acidification and temperature rises, as separate factors. Such relative resilience may be a result of the highly variable environment they inhabit.
Global Change Biology, 2002
Growth rates, photosynthetic responses and the activity, amount and CO 2 affinity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) were determined for common marine macroalgae grown in seawater (containing 14.5 + 2.1 mM CO 2) or CO 2enriched seawater (averaging 52.8 + 19.2 mM CO 2). The algae were grown in 40 L fiberglass tanks (outdoor) for 4±15 weeks and in a field experimental setup for 5 days. Growth rates of the species studied (representing the three major divisions, i.e. Chlorophyta, Rhodophyta and Phaeophyta) were generally not significantly affected by the increased CO 2 concentrations in the seawater medium. Rubisco characteristics of algae cultivated in CO 2-enriched seawater were similar to those of algae grown in nonenriched seawater. The lack of response of photosynthetic traits in these aquatic plants is likely to be because of the presence of CO 2 concentrating mechanisms (CCMs) which rely on HCO 3 ± utilization, the inorganic carbon (Ci) form that dominates the total Ci pool available in seawater. Significant changes on the productivity of these particular marine algae species would not be anticipated when facing future increasing atmospheric CO 2 levels.
Global Change Biology, 2002
Growth rates, photosynthetic responses and the activity, amount and CO 2 affinity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) were determined for common marine macroalgae grown in seawater (containing 14.5 + 2.1 mM CO 2) or CO 2enriched seawater (averaging 52.8 + 19.2 mM CO 2). The algae were grown in 40 L fiberglass tanks (outdoor) for 4±15 weeks and in a field experimental setup for 5 days. Growth rates of the species studied (representing the three major divisions, i.e. Chlorophyta, Rhodophyta and Phaeophyta) were generally not significantly affected by the increased CO 2 concentrations in the seawater medium. Rubisco characteristics of algae cultivated in CO 2-enriched seawater were similar to those of algae grown in nonenriched seawater. The lack of response of photosynthetic traits in these aquatic plants is likely to be because of the presence of CO 2 concentrating mechanisms (CCMs) which rely on HCO 3 ± utilization, the inorganic carbon (Ci) form that dominates the total Ci pool available in seawater. Significant changes on the productivity of these particular marine algae species would not be anticipated when facing future increasing atmospheric CO 2 levels.
Temperate and tropical brown macroalgae thrive, despite decalcification, along natural CO2 gradients
Predicting the impacts of ocean acidification on coastal ecosystems requires an understanding of the effects on macroalgae and their grazers, as these underpin the ecology of rocky shores. Whilst calcified coralline algae (Rhodophyta) appear to be especially vulnerable to ocean acidification, there is a lack of information concerning calcified brown algae (Phaeophyta), which are not obligate calcifiers but are still important producers of calcium carbonate and organic matter in shallow coastal waters. Here, we compare ecological shifts in subtidal rocky shore systems along CO2 gradients created by volcanic seeps in the Mediterranean and Papua New Guinea, focussing on abundant macroalgae and grazing sea urchins. In both the temperate and tropical systems the abundances of grazing sea urchins declined dramatically along CO2 gradients. Temperate and tropical species of the calcifying macroalgal genus Padina (Dictyoaceae, Phaeophyta) showed reductions in CaCO3 content with CO2 enrichment. In contrast to other studies of calcified macroalgae, however, we observed an increase in the abundance of Padina spp. in acidified conditions. Reduced sea urchin grazing pressure and significant increases in photosynthetic rates may explain the unexpected success of decalcified Padina spp. at elevated levels of CO2. This is the first study to provide a comparison of ecological changes along CO2 gradients between temperate and tropical rocky shores. The similarities we found in the responses of Padina spp. and sea urchin abundance at several vent systems increases confidence in predictions of the ecological impacts of ocean acidification over a large geographical range.
Three macroalgal species belonging to Chlorophyta (Ulva rigida), Rhodophyta (Ellisolandia elongata) and Phaeophyceae (Heterokontophyta; Cystoseira tamariscifolia), naturally growing at the same shore level and representing 3 morpho-functional groups, were exposed to short-term changes in temperature under different carbon and nitrogen regimes. Experiments were conducted in outdoor tanks at 4 combinations of carbon and nitrogen levels under reduced solar radiation. In vivo chl a fluorescence parameters and pigment contents were monitored to assess diurnal physiological responses and potential for recovery. Strong fluctuations in chl a fluorescence parameters, but not in chl a content, were observed in response to diurnal variation in solar radiation and light climate within the tanks; sensitivity varied between algal species and, in some cases, depended on the carbon and nitrogen regime. Nitrogen uptake was similarly high in U. rigida and E. elongata and lowest in C. tamariscifolia. In U. rigida and E. elongata, chl a concentrations decreased after high-carbon treatments. Effective photosystem II quantum efficiency was reduced in all species at noon, and lowest in C. tamariscifolia. The results highlight the complexity of physiological short-term acclimations which were most likely linked to biochemical changes at the cellular level. Long-term experiments are required in future for more comprehensive investigation of the observed interactive effects of the different environmental parameters.
Photosynthesis of marine macroalgae and seagrasses in globally changing CO2 environments
Marine Ecology Progress Series, 1996
Photosynthetic rates of many marine macroalgae are saturated by the present day inorganic carbon (Ci) composition of seawater, while those of seagrasses (or marine angiosperms) are CO1limited. In this study we attempted to simulate the Ci conditions of near-shore seawater during the time that seagrasses colonised the sea (in the Cretaceous), and compare the photosynthetic performance of representatives of the 2 plant groups under those versus present day conditions. The results show that the seagrasses have an affinity for Ci at least as high as the algae under the low pH and high C02/HC03' concentration ratios simulating near-shore areas of the Cretaceous seas, indicating that their photosynthetic capacity then matched that of macroalgae. However, in the high pH and high COz/HCO?-ratlos of today, their a f f~n~t y for Ci is lower than that of the macroalgae, and it is suggested that this deficiency renders them a lower ability for Ci utilisation. This situat~on may possibly be reversed again as global CO2 levels of the atmosphere and, consequently, of near-shore marine habitats increase in the future.