Posts Tagged 'algae'

Impact of ocean acidification and warming on the diversity and the functioning of macroalgal communities (full thesis in French)

Predicted ocean acidification and warming for the end of the century may have drastic consequences on the structure and functioning of marine ecosystems. However, a lack of knowledge persists on the impact of future changes on the response of marine communities. This thesis aims to provide new understanding of the impact of ocean acidification and warming at the community level. For this, two ecosystems have been considered: rockpools, characterized by high physico-chemical variations, and maerl beds, with smaller variations. In the laboratory, artificial assemblages were created from the main calcareous and fleshy macroalgal and grazer species present in these two ecosystems. Created assemblages have been subjected to ambient and future temperature and pCO2 conditions. Ocean acidification and warming altered the structure and functioning of maerl bed assemblages, through an increase in the productivity of non-calcareous macroalgae and a decline in maërl calcification rates. The physiology of grazers is negatively impacted by future changes, which altered assemblages’ trophic structure. On the other hand, ocean acidification and warming had no effect on the productivity of rockpool assemblages. The highly variable environment may thus increase the resistance of rockpool communities to future changes, compared to communities from more stable environments, such as maerl beds.

Continue reading ‘Impact of ocean acidification and warming on the diversity and the functioning of macroalgal communities (full thesis in French)’

Effects of CO2 supply on growth and photosynthetic ability of young sporophytes of the economic seaweed Sargassum fusiforme (Sargassaceae, Phaeophyta)

Young sporophytes of Sargassum fusiforme were cultured at decreased CO2 (20 μatm), ambient CO2 (400 μatm), and high CO2 (1000 μatm), and then the quantum efficiency of open photosystem II (Fv′/Fm′), initial slope of the rapid light curves (α), and relative maximum photosynthetic electron transport rate (rETRm) of the algae under different temperatures and light levels were measured. The study aimed to investigate how the decreased CO2 and high CO2 supply affected the growth and photosynthetic functions of S. fusiforme young sporophytes. While both lowered and increased CO2 supply significantly reduced the growth rates of the alga, greater declines were observed under decreased CO2. The Fv′/Fm′, α, and rETRm of alga remained stable after short-term (120 min) exposures to 18, 22, and 26 °C, as well as to highlight (300 μmol photons m−2 s−1), with no significant difference among the three CO2 supply treatments. Hence, neither decreased nor increased CO2 affected the photosynthetic responses of S. fusiforme young sporophytes to temperature and high light. However, the Fv′/Fm′ of the three CO2 treatments declined by 72% under 60 μmol photons m−2 s−1, suggesting its sensitivity to short-term low light. These observations are crucial for the improved management of S. fusiforme for commercial farming, while ensuring its sustainable production and supply amid seawater pH shifts brought about by global climate change.

Continue reading ‘Effects of CO2 supply on growth and photosynthetic ability of young sporophytes of the economic seaweed Sargassum fusiforme (Sargassaceae, Phaeophyta)’

Nitrogen enrichment offsets direct negative effects of ocean acidification on a reef-building crustose coralline alga

Ocean acidification (OA) and nutrient enrichment threaten the persistence of near shore ecosystems, yet little is known about their combined effects on marine organisms. Here, we show that a threefold increase in nitrogen concentrations, simulating enrichment due to coastal eutrophication or consumer excretions, offset the direct negative effects of near-future OA on calcification and photophysiology of the reef-building crustose coralline alga, Porolithon onkodes. Projected near-future pCO2 levels (approx. 850 µatm) decreased calcification by 30% relative to ambient conditions. Conversely, nitrogen enrichment (nitrate + nitrite and ammonium) increased calcification by 90–130% in ambient and high pCO2 treatments, respectively. pCO2 and nitrogen enrichment interactively affected instantaneous photophysiology, with highest relative electron transport rates under high pCO2 and high nitrogen. Nitrogen enrichment alone increased concentrations of the photosynthetic pigments chlorophyll a, phycocyanin and phycoerythrin by approximately 80–450%, regardless of pCO2. These results demonstrate that nutrient enrichment can mediate direct organismal responses to OA. In natural systems, however, such direct benefits may be counteracted by simultaneous increases in negative indirect effects, such as heightened competition. Experiments exploring the effects of multiple stressors are increasingly becoming important for improving our ability to understand the ramifications of local and global change stressors in near shore ecosystems.

Continue reading ‘Nitrogen enrichment offsets direct negative effects of ocean acidification on a reef-building crustose coralline alga’

Effects of ocean acidification on algae growth and feeding rates of juvenile sea urchins


• Ocean acidification increase the feeding rates of juveniles of P. lividus on algae reared at low pH.
• However the effects of ocean acidification on feeding rates of D. africanum were not differences between algae reared under low pH and control pH.
• This investigation highlights indirect effects of ocean acidification such as increase in herbivores pressure as consequence of change in algae palatability.
• Ocean acidification affects growth of 9 algae species from Canary Islands.
• A future scenario of climate change could affect the palatability of algae and their growth.


The recent decrease in seawater pH has stimulated a great deal of research on the effects of ocean acidification on various organisms. Most of these studies have mainly focused on the direct effects of acidification on organisms. However, the effects on ecological interactions have been poorly studied. In this paper we have focused on determining the effects of acidification on feeding rates of two species of sea urchins, Paracentrotus lividus and Diadema africanum through laboratory experiments. Nine algae species were reared under two pH treatmens (ph = 8.1 vs. pH = 7.6) for 10 days. We evaluated possible changes in calcification rates, growth and internal structure. Then these algae were offered to juvenile sea urchins for 7 days, evaluating the consumption rates of juvenile sea urchins under these different pH conditions. The algae reared in the control treatment showed higher growth rates and concentration of calcium carbonate, however no internal structural changes were observed in any algae. Juvenile Paracentrotus lividus showed higher consumption rates on algae previously subjected to pH 7.6 than on algae reared under control conditions and between algae species in low pH.The algae most consumed were C. liebetruthii, C. abies-marina and C. elongata by P. lividus juveniles from low pH treatment. However in D. africanum the feeding rates were similar between treatments. This study demonstrated the negative effects of low pH on various species of algae in growth, and indirectly the increase in herbivory rates of juvenile sea urchins on algae reared under low pH.

Continue reading ‘Effects of ocean acidification on algae growth and feeding rates of juvenile sea urchins’

CO2 emissions boost the benefits of crop production by farming damselfish

Farming is a technique employed by both humans and animals to enhance crop yields, allowing their populations to increase beyond the natural carrying capacity of the environment. Using volcanic CO2 vents, we investigate how a species of herbivorous fish (the black scalyfin Parma alboscapularis) may use increasing anthropogenic CO2 emissions to enhance its crop yields. We found that these farming fish can take advantage of this resource enrichment, to grow crops within smaller territories and increase the capacity of the environment to support more densely packed fish populations.

Continue reading ‘CO2 emissions boost the benefits of crop production by farming damselfish’

Effects of ocean acidification on the levels of primary and secondary metabolites in the brown macroalga Sargassum vulgare at different time scales


Sargassum vulgare growing at CO2 vents was compared with those growing at control site.
S. vulgare from control site was transplanted to CO2 vents for 2 weeks.
• In short-term responses, S. vulgare showed increased level of sugars, PUFAs, and EAAs.
• Natural population at vents showed decreased sugars, PUFAs, phenols, and increased EAAs.
• Nutritional values of algae will decrease under acidification in long time scale.


Most of the studies regarding the impact of ocean acidification on macroalgae have been carried out for short-term periods, in controlled laboratory conditions, thus hampering the possibility to scale up the effects on long-term. In the present study, the volcanic CO2 vents off Ischia Island were used as a natural laboratory to investigate the metabolic response of the brown alga Sargassum vulgare to acidification at different time scales. For long-term effects, algal populations naturally growing at acidified and control sites were compared. For short-term responses, in situ reciprocal transplants from control to acidified site and vice-versa were performed. Changes in the levels of sugars, fatty acids (FAs), amino acids (AAs), antioxidants, and phenolic compounds were examined. Our main finding includes variable metabolic response of this alga at different time scales to natural acidification. The levels of sugars, FAs, and some secondary metabolites were lower in the natural population at the acidified site, whereas the majority of AAs were higher than those detected in thalli growing at control site. Moreover, in algae transplanted from control to acidified site, soluble sugars (glucose and mannose), majority of AAs, and FAs increased in comparison to control plants transplanted within the same site. The differences in the response of the macroalga suggest that the metabolic changes observed in transplants may be due to acclimation that supports algae to cope with acidification, thus leading to adaptation to lowered pH in long time scale.

Graphical abstract

Unlabelled Image

Continue reading ‘Effects of ocean acidification on the levels of primary and secondary metabolites in the brown macroalga Sargassum vulgare at different time scales’

The role of irradiance and C-use strategies in tropical macroalgae photosynthetic response to ocean acidification

Fleshy macroalgae may increase photosynthesis with greater CO2 availability under ocean acidification (OA) and outcompete calcifying macroalgae important for tropical reef accretion. Macroalgae use energy-dependent carbon concentrating mechanisms (CCMs) to take up HCO3, the dominant inorganic carbon for marine photosynthesis, but carbon-use strategies may depend on the pCO2, pH and irradiance. We examined photosynthesis in eight tropical macroalgae across a range of irradiances (0–1200 μmol photon m−2 s−1), pH levels (7.5–8.5) and CO2 concentrations (3–43 μmol kg−1). Species-specific CCM strategies were assessed using inhibitors and δ13C isotope signatures. Our results indicate that the log of irradiance is a predictor of the photosynthetic response to elevated pCO2 (R2 > 0.95). All species utilized HCO3, exhibited diverse C-use pathways and demonstrated facultative HCO3 use. All fleshy species had positive photosynthetic responses to OA, in contrast to a split amongst calcifiers. We suggest that shifts in photosynthetically-driven tropical macroalgal changes due to OA will most likely occur in moderate to high-irradiance environments when CCMs are ineffective at meeting the C-demands of photosynthesis. Further, facultative use of HCO3 allows greater access to CO2 for photosynthesis under OA conditions, particularly amongst fleshy macroalgae, which could contribute to enhance fleshy species dominance over calcifiers.

Continue reading ‘The role of irradiance and C-use strategies in tropical macroalgae photosynthetic response to ocean acidification’

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Ocean acidification in the IPCC AR5 WG II

OUP book