Posts Tagged 'algae'

Response of coralline algae Porolithon onkodes to elevated seawater temperature and reduced pH

Coralline algae (CA), a type of primary calcifying producer presented in coastal ecosystems, are considered one of the highly sensitive organisms to marine environmental change. However, experimental studies on coralline algae responses to elevated seawater temperature and reduced pH have documented either contradictory or opposite results. In this study, we analysed the growth and physiological responses of coralline algae Porolithon onkodes to the elevated temperature (30.8°C) and reduced pH (7.8). The aim of this analysis was to observe the direct and combined effects, while elucidating the growth and photosynthesis in this response. It was demonstrated that the algae thallus growth rate and photosynthesis under elevated temperature were depressed by 21.5% and 14.9% respectively. High pCO2 enhanced the growth and photosynthesis of the thallus at ambient temperature, while they were deceased when both temperature and pCO2 were elevated. CA is among the most sensitive organisms to ocean acidification (OA) because of their precipitate high Mg-calcite. We hypothesize that coralline algae could increase their calcification rate in order to counteract the effects of moderate acidification, but offset by the effect of elevated temperature. Accordingly, our results also support the conclusion that global warming (GW) is a stronger threat to algal performance than OA. Our findings are also proposed that coralline algae may be more
resilient under OA than GW.

Continue reading ‘Response of coralline algae Porolithon onkodes to elevated seawater temperature and reduced pH’

Biogenic acidification of Portuguese oyster Magallana angulata mariculture can be mediated through introducing brown seaweed Sargassum hemiphyllum

Highlights

• Monoculture of oysters produces excess CO2, affecting carbon fluxes.

• Seaweed can eliminate CO2 released by oysters.

• Multi-trophic culture of oysters and seaweed can mitigate oysters monoculture negative impacts.

Abstract

The physiological responses of aquaculture organisms (e.g., oyster and seaweed) have the potential to affect seawater carbon fluxes and subsequently are affected by these seawater changes. In this study, a laboratory experiment and a field mesocosm experiment were carried out in Daya Bay, southern China. In the laboratory experiment, Portuguese oyster Magallana angulata and the brown seaweed Sargassum hemiphyllum were mono-cultured in 20-L transparent glass bottles for 24 h. Water sample were collected at four incubation time points (i.e. 0 h, 4 h, 12 h and 24 h) to examine their physiological responses across the incubation period. The results showed that the oyster calcification rate was not significantly changed among 4 h, 12 h and 24 h. On the other hand, during the 24 h incubation time, the oyster respiration rate, seawater pH, dissolved oxygen (DO), and CO32– concentration were significantly declined, but the seawater CO2 concentration was increased. For the seaweed, from 0 h to 12 h, seawater CO2 and HCO3– concentrations were significantly declined. However, the seawater pH and DO concentration were increased. In the field experiment, oyster and seaweed were cultured in mesocosm bags. The effects of different culture models of M. angulata and S. hemiphyllum (i.e. oyster monoculture, seaweed monoculture and oyster-seaweed co-culture) on seawater CO2‑carbonate system and air-sea CO2 flux (FCO2) were investigated after 24 h incubation. The results showed that DIC, HCO3– and CO2 concentrations and the partial pressure of CO2 in co-culture bags were significantly lower than the control bags (without any culture organisms) and oyster bags, indicated that S. hemiphyllum can effectively absorb the CO2 released by the oysters. The negative values of air-sea FCO2 in the co-culture bags represent a CO2 sink from the atmosphere to the sea. These results demonstrated that aquaculture organism monoculture could result in a stress for itself, and there could be an interspecies mutual benefit for both M. angulata and S. hemiphyllum in the co-culture system. The negative environmental impacts of mono-trophic oyster aquaculture in this view could be mediated with the multi-trophic inclusion of seaweed.

Continue reading ‘Biogenic acidification of Portuguese oyster Magallana angulata mariculture can be mediated through introducing brown seaweed Sargassum hemiphyllum’

Clam feeding plasticity reduces herbivore vulnerability to ocean warming and acidification

Ocean warming and acidification affect species populations, but how interactions within communities are affected and how this translates into ecosystem functioning and resilience remain poorly understood. Here we demonstrate that experimental ocean warming and acidification significantly alters the interaction network among porewater nutrients, primary producers, herbivores and burrowing invertebrates in a seafloor sediment community, and is linked to behavioural plasticity in the clam Scrobicularia plana. Warming and acidification induced a shift in the clam’s feeding mode from predominantly suspension feeding under ambient conditions to deposit feeding with cascading effects on nutrient supply to primary producers. Surface-dwelling invertebrates were more tolerant to warming and acidification in the presence of S. plana, most probably due to the stimulatory effect of the clam on their microalgal food resources. This study demonstrates that predictions of population resilience to climate change require consideration of non-lethal effects such as behavioural changes of key species.

Continue reading ‘Clam feeding plasticity reduces herbivore vulnerability to ocean warming and acidification’

A coralline alga gains tolerance to ocean acidification over multiple generations of exposure

Crustose coralline algae play a crucial role in the building of reefs in the photic zones of nearshore ecosystems globally, and are highly susceptible to ocean acidification. Nevertheless, the extent to which ecologically important crustose coralline algae can gain tolerance to ocean acidification over multiple generations of exposure is unknown. We show that, while calcification of juvenile crustose coralline algae is initially highly sensitive to ocean acidification, after six generations of exposure the effects of ocean acidification disappear. A reciprocal transplant experiment conducted on the seventh generation, where half of all replicates were interchanged across treatments, confirmed that they had acquired tolerance to low pH and not simply to laboratory conditions. Neither exposure to greater pH variability, nor chemical conditions within the micro-scale calcifying fluid internally, appeared to play a role in fostering this capacity. Our results demonstrate that reef-accreting taxa can gain tolerance to ocean acidification over multiple generations of exposure, suggesting that some of these cosmopolitan species could maintain their critical ecological role in reef formation.

Continue reading ‘A coralline alga gains tolerance to ocean acidification over multiple generations of exposure’

Impact of ocean acidification on the metabolome of the brown macroalgae Lobophora rosacea from New Caledonia

Highlights

• Metabolomic responses of Lobophora rosacea are compared at different pH.

• Significant metabolomic differences are observed in situ between control and lower pH.

• An ex situ experiment demonstrates a short-term effect of ocean acidification.

• The concentration of metabolites related to lobophorenols decreases at low pH.

• We suggest a down-regulation of metabolic pathways involving oxylipins or their transformation when decreasing the pH

Abstract

Macroalgae are critical components of coral reef ecosystems. Yet, they compete for space with corals, and in case of environmental disturbances, they are increasingly involved in phase-shifts from coral-dominated to macroalgae-dominated reefs. As regard to climate change, ocean acidification (OA) has been shown to be detrimental to corals and could favor macroalgal proliferations. However, little is known about the effects of OA on macroalgal phenotypes. Comparative metabolomic studies are particularly relevant to assess phenotypic responses of macroalgae to stress as some seaweed are known to produce a large diversity of specialized metabolites involved in various ecological functions. The main aim of our study was to explore the impact of OA on the metabolome of brown macroalgae using Lobophora rosacea as a model species. This species is widespread in New Caledonian lagoons where it is a key component of coral-algal interactions. Metabolomic changes were analyzed using Liquid Chromatography-Mass Spectrometry (UPLC-HRMS) applied to three different OA scenarii: low and variable pH over a long-term timescale (in situ at Bouraké), low and constant pH over a short-term timescale (ex situ experiment), and current pH (control). Different metabotypes were defined in diverse pH conditions, and a significant decrease in some specialized metabolites concentrations was noticed at low pH including lobophorenols B and C as well as other oxylipin derivatives. We suggest a down-regulation of metabolic pathways involving lobophorenols, in low pH conditions, or their transformation, which is in accordance with the optimal defense theory. In addition, we used Microtox® bioassays as a proxy for macroalgal toxicity and found no significant differences between low pH and control samples. This study details the first metabolomic-based study on a fleshy macroalgae in response to OA and provides new insights for this important functional group producing a large number of metabolites in response to their close environment.

Continue reading ‘Impact of ocean acidification on the metabolome of the brown macroalgae Lobophora rosacea from New Caledonia’

Ocean acidification affects biological activities of seaweeds: a case study of Sargassum vulgare from Ischia volcanic CO2 vents

Highlights

  • Bioactivities of S. vulgare from Ischia CO2 vents and nearby control site were analysed.
  • Elevated DIC increases polysaccharide content in the algae at CO2 vents.
  • Algal extract from acidified population showed higher antimicrobial, and antiprotozoal activity.
  • Acidified population showed pronounced antimutagenic potential and anticancer activities.

Abstract

We utilized volcanic CO2 vents at Castello Aragonese off Ischia Island as a natural laboratory to investigate the effect of lowered pH/elevated CO2 on the bioactivities of extracts from fleshy brown algae Sargassum vulgare C. Agardh. We analysed the carbohydrate levels, antioxidant capacity, antibacterial, antifungal, antiprotozoal, anticancer properties and antimutagenic potential of the algae growing at the acidified site (pH ∼ 6.7) and those of algae growing at the nearby control site Lacco Ameno (pH∼8.1). The results of the present study show that the levels of polysaccharides fucoidan and alginate were higher in the algal population at acidified site. In general, extracts for the algal population from the acidified site showed a higher antioxidant capacity, antilipidperoxidation, antibacterial, antifungal, antiprotozoal, anticancer activities and antimutagenic potential compared to the control population. The increased bioactivity in acidified population could be due to elevated levels of bioactive compounds of algae and/or associated microbial communities. In this snapshot study, we performed bioactivity assays but did not characterize the chemistry and source of presumptive bioactive compounds. Nevertheless, the observed improvement in the medicinal properties of S. vulgare in the acidified oceans provides a promising basis for future marine drug discovery.

Continue reading ‘Ocean acidification affects biological activities of seaweeds: a case study of Sargassum vulgare from Ischia volcanic CO2 vents’

Zinc toxicity alters the photosynthetic response of red alga Pyropia yezoensis to ocean acidification

The globally changing environmental climate, ocean acidification, and heavy metal pollution are of increasing concern. However, studies investigating the combined effects of ocean acidification and zinc (Zn) exposure on macroalgae are very scarce. In this study, the photosynthetic performance of the red alga Pyropia yezoensis was examined under three different concentrations of Zn (control, 25 (medium), and 100 (high) μg L−1) and pCO2 (400 (ambient) and 1000 (high) μatm). The results showed that higher Zn concentrations resulted in increased toxicity for P. yezoensis, while ocean acidification alleviated this negative effect. Ocean acidification increased the relative growth rate of thalli under both medium and high Zn concentrations. The net photosynthetic rate and respiratory rate of thalli also significantly increased in response under ocean acidification, when thalli were cultured under both medium and high Zn concentrations. Malondialdehyde levels decreased under ocean acidification, compared to ambient CO2 conditions and either medium or high Zn concentrations. The activity of superoxide dismutase increased in response to high Zn concentrations, which was particularly apparent at high Zn concentration and ocean acidification. Immunoblotting tests showed that ocean acidification increased D1 removal, with increasing expression levels of the PSII reaction center proteins D2, CP47, and RbcL. These results suggested that ocean acidification could alleviate the damage caused by Zn exposure, thus providing a theoretical basis for a better prediction of the impact of global climate change and heavy metal contamination on marine primary productivity in the form of seaweeds.

Continue reading ‘Zinc toxicity alters the photosynthetic response of red alga Pyropia yezoensis to ocean acidification’


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Ocean acidification in the IPCC AR5 WG II

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