Posts Tagged 'algae'

Ecophysiological responses to elevated CO2 and temperature in Cystoseira tamariscifolia (Phaeophyceae)

Ocean acidification increases the amount of dissolved inorganic carbon (DIC) available in seawater which can benefit photosynthesis in those algae that are currently carbon limited, leading to shifts in the structure and function of seaweed communities. Recent studies have shown that ocean acidification-driven shifts in seaweed community dominance will depend on interactions with other factors such as light and nutrients. The study of interactive effects of ocean acidification and warming can help elucidate the likely effects of climate change on marine primary producers. In this study, we investigated the ecophysiological responses of Cystoseira tamariscifolia (Hudson) Papenfuss. This large brown macroalga plays an important structural role in coastal Mediterranean communities. Algae were collected from both oligotrophic and ultraoligotrophic waters in southern Spain. They were then incubated in tanks at ambient (ca. 400–500 ppm) and high CO2 (ca. 1200–1300 ppm), and at 20 °C (ambient temperature) and 24 °C (ambient temperature +4 °C). Increased CO2 levels benefited the algae from both origins. Biomass increased in elevated CO2 treatments and was similar in algae from both origins. The maximal electron transport rate (ETRmax), used to estimate photosynthetic capacity, increased in ambient temperature/high CO2 treatments. The highest polyphenol content and antioxidant activity were observed in ambient temperature/high CO2 conditions in algae from both origins; phenol content was higher in algae from ultraoligotrophic waters (1.5–3.0%) than that from oligotrophic waters (1.0–2.2%). Our study shows that ongoing ocean acidification can be expected to increase algal productivity (ETRmax), boost antioxidant activity (EC50), and increase production of photoprotective phenols. Cystoseira tamariscifolia collected from oligotrophic and ultraoligotrophic waters were able to benefit from increases in DIC at ambient temperatures. Warming, not acidification, may be the key stressor for this habitat as CO2 levels continue to rise.

Continue reading ‘Ecophysiological responses to elevated CO2 and temperature in Cystoseira tamariscifolia (Phaeophyceae)’

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’

Primary utricle structure of six Halimeda species and potential relevance for ocean acidification tolerance

Variations in utricle morphology may be responsible for different tolerances to ocean acidification (OA) within the macroalgal genus Halimeda, an important sediment producer on reefs. However, differences in species’ utricle morphology and their relationship to calcification and crystal formation have not been well articulated. In the present study, we characterized the utricle morphologies of six Halimeda species. Primary utricle ultrastructure was quantitatively and qualitatively compared to tissue inorganic content and crystal microstructure. Morphologies differed across species and several morphometric relationships were revealed. Primary utricle size (r2=0.70) and diffusion pathway length (r2=0.87) had inverse relationships with inorganic content based on regression analyses, and corresponded to crystal microstructure form. Species with large utricles and long diffusion pathways contained more narrow (~0.15 μm) aragonite needles and minimal micro-anhedral crystal formations. In contrast, species with small utricles and short diffusion pathways elucidated aggregates of micro-anhedral crystals and wider aragonite needles (~0.30 μm). Species’ utricle characteristics generally corresponded to specific evolutionary lineages. Thus, characteristics of Halimeda utricle morphology may control long-term adaptive responses to OA, an idea articulated in the broader literature.

Continue reading ‘Primary utricle structure of six Halimeda species and potential relevance for ocean acidification tolerance’

Functional genomic analysis of corals from natural CO2-seeps reveal core molecular responses involved in acclimatization to ocean acidification

Little is known about the potential for acclimatization or adaptation of corals to ocean acidification and even less about the molecular mechanisms underpinning these processes. Here we examine global gene expression patterns in corals and their intracellular algal symbionts from two replicate population pairs in Papua New Guinea that have undergone long-term acclimatization to natural variation in pCO2. In the coral host, only 61 genes were differentially expressed in response to pCO2 environment, but the pattern of change was highly consistent between replicate populations, likely reflecting the core expression homeostasis response to ocean acidification. Functional annotations highlight lipid metabolism and a change in the stress response capacity of corals as a key part of this process. Specifically, constitutive downregulation of molecular chaperones was observed, which may impact response to combined climate-change related stressors. Elevated CO2 has been hypothesized to benefit photosynthetic organisms but expression changes of in hospite Symbiodinium in response to acidification were greater and less consistent among reef populations. This population-specific response suggests hosts may need to adapt not only to an acidified environment, but also to changes in their Symbiodinium populations that may not be consistent among environments. This process adds another challenging dimension to the physiological process of coping with climate change.

Continue reading ‘Functional genomic analysis of corals from natural CO2-seeps reveal core molecular responses involved in acclimatization to ocean acidification’

Diurnal pH fluctuations of seawater influence the responses of an economic red macroalga Gracilaria lemaneiformis to future CO2-induced seawater acidification

The diurnal fluctuation of pH in costal seawater in sea-farming areas is larger than that the pH reduction induced by progressive seawater acidification by the end of this century. To best understand how seawater acidification influences the primary productivity of macroalgae in coastal waters under the pH fluctuation conditions, Gracilaria lemaneiformis, an important economical red macroalgae, was selected in our study. pH fluctuation (pH-F, high density cultivation) and pH stabilization (pH-S, low density cultivation) conditions were set to study the effects of seawater acidification on the production of G. lemaneiformis experiencing different pH fluctuation conditions. The results showed that seawater acidification significantly decreased the relative growth rate (RGR) of G. lemaneiformis grown at pH-S condition, but the enhancement of RGR was found in the pH-F-grown thalli. The similar trends were showed in the net photosynthetic rates of G. lemaneiformis. The different responses of RGR and net photosynthetic rates to seawater acidification between pH-S and pH-F conditions might be attributed to different daily pH variations. Under pH-S treatment, pH values varied < 0.2 units with all values < 8.3, indicating a relative sufficient CO2 supply. Therefore, the effect of seawater acidification was more determined by the negative effect of elevated acidity rather than positive effect of the increased CO2 supply. While under pH-F level, pH values varied > 0.6 units and it could reach 9.09 in the LC-grown thalli, suggesting limited CO2 supply as CO2 level decreases about 14.1 μmol kg− 1 (from 15.8 to 0.7 μmol kg− 1) with the increase of pH (from 8.11 to 9.09). Increased CO2 at the seawater acidification condition could significantly relieve this carbon resource limitation, resulting in the enhancement of RGR of HC-grown plants.

Statement of relevance: It can be predicted that the carbon resource limitation for high-density cultivation of G. lemaneiformis will be significantly relieved by coastal ocean acidification, resulting in the production increases in the future ocean, which can provide some reference values for the aquaculture of macroalgae.

Continue reading ‘Diurnal pH fluctuations of seawater influence the responses of an economic red macroalga Gracilaria lemaneiformis to future CO2-induced seawater acidification’

Mediterranean versus Red sea corals facing climate change, a transcriptome analysis

The anthropogenic increase in atmospheric CO2 that drives global warming and ocean acidification raises serious concerns regarding the future of corals, the main carbonate biomineralizers. Here we used transcriptome analysis to study the effect of long-term gradual temperature increase (annual rate), combined with lowered pH values, on a sub-tropical Red Sea coral, Stylophora pistillata, and on a temperate Mediterranean symbiotic coral Balanophyllia europaea. The gene expression profiles revealed a strong effect of both temperature increase and pH decrease implying for synergism response. The temperate coral, exposed to a twice as high range of seasonal temperature fluctuations than the Red Sea species, faced stress more effectively. The compensatory strategy for coping apparently involves deviating cellular resources into a massive up-regulation of genes in general, and specifically of genes involved in the generation of metabolic energy. Our results imply that sub-lethal, prolonged exposure to stress can stimulate evolutionary increase in stress resilience.

Continue reading ‘Mediterranean versus Red sea corals facing climate change, a transcriptome analysis’

Daily variation in net primary production and net calcification in coral reef communities exposed to elevated pCO2

The threat represented by ocean acidification (OA) for coral reef has received considerable attention because of the sensitivity of calcifiers to changing water carbonate chemistry. However most studies have focused on the organismic response of calcification to OA, and only a few have addressed community-level effects, or investigated parameters other than calcification, such as photosynthesis. Light (Photosynthetically Active Radiation, PAR) is a driver of biological processes on coral reefs, and the possibility that these processes might be perturbed by OA has important implications for community function. Here we investigate how CO2 enrichment affects the relationships between PAR and community net O2 production (Pnet), and between PAR and community net calcification (Gnet), using experiments on three coral communities constructed to match (i) the back reef of Moorea, French Polynesia, (ii) the fore reef of Moorea, and (iii) the reef flat of Oahu, Hawaii. The results were used to test the hypothesis that OA affects the relationship between Pnet and Gnet. For the three communities tested, pCO2 did not affect the Pnet-PAR relationship, but it affected the intercept of the hyperbolic tangent curve fitting the Gnet-PAR relationship for both reef communities in Moorea (but not in Oahu). For the three communities, the slopes of the linear relationships between Pnet and Gnet were not affected by OA, although the intercepts were depressed by the inhibitory effect of high pCO2 on Gnet. Our result indicates that OA can modify the balance between net calcification and net photosynthesis of reef communities by depressing community calcification, but without affecting community photosynthesis.

Continue reading ‘Daily variation in net primary production and net calcification in coral reef communities exposed to elevated pCO2’


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Ocean acidification in the IPCC AR5 WG II

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