Posts Tagged 'light'

Effects of light intensity on the photosynthetic responses of Sargassum fusiforme seedlings to future CO2 rising

Mariculture of the economically important seaweed will likely be affected by the combined conditions of ocean acidification that resulting from increasing CO2 rising and decreased light levels, especially under high culture intensity and high biomass accumulation. To examine this coupling effect on the photosynthetic performance of Sargassum fusiforme seedlings, we cultured seedlings of this alga under different light and CO2 levels. Under low light conditions, elevated CO2 significantly decreased the photosynthesis of S. fusiforme seedlings, including a decreased photosynthetic electron transport rate. Seedlings grown under the low light intensity exhibited higher photosynthetic rates and compensation irradiance, and displayed higher photosynthetic pigment contents and light absorption than seedlings grown under high light intensity, providing strong evidence of photosynthetic acclimation to low light. However, the captured light and energy were insufficient to support photosynthesis in acidified seawater regardless of increased dissolved inorganic carbon, resulting in declined carbohydrate and biomass accumulation. This indicated that S. fusiforme photosynthesis was more sensitive to acidified seawater in its early growth stage, and strongly affected by light intensity. Future research should evaluate the practical manipulation of biomass accumulation and mariculture densities during the early culture period at the CO2 level predicted for the end of the century.

Continue reading ‘Effects of light intensity on the photosynthetic responses of Sargassum fusiforme seedlings to future CO2 rising’

CO2 modulation of the rates of photosynthesis and light-dependent O2 consumption in Trichodesmium

We established the relationship between gross photosynthetic O2 evolution and light-dependent O2 consumption in Trichodesmium erythraeum IMS101 acclimated to three targeted pCO2 concentrations (180 µmol mol-1 = low-CO2, 380 µmol mol-1 = mid-CO2 and 720 µmol mol-1 = high-CO2). We found that biomass (carbon) specific, light-saturated maximum net O2 evolution rates (PnC,max) and acclimated growth rates increased from low- to mid-CO2, but did not differ significantly between mid- and high-CO2. Dark respiration rates were five-times higher than required to maintain cellular metabolism, suggesting that respiration provides a substantial proportion of the ATP and reductant for N2 fixation. Oxygen uptake increased linearly with gross O2 evolution across light intensities ranging from darkness to 1100 µmol photons m-2 s-1. The slope of this relationship decreased with increasing CO2, which we attribute to the increased energetic cost of operating the carbon concentrating mechanism (CCM) at lower CO2 concentrations. Our results indicate that net photosynthesis and growth of T. erythraeum IMS101 would have been severely CO2 limited at the last glacial maximum, but that the direct effect of future increases of CO2 may only cause marginal increases in growth.

Continue reading ‘CO2 modulation of the rates of photosynthesis and light-dependent O2 consumption in Trichodesmium’

Vulnerability of juvenile hermit crabs to reduced seawater pH and shading

Highlights

• Local impacts may potentially increase effects of global environmental changes.
• We assessed combined effects of reduced pH and shading caused by harbor structures.
• Reduced seawater pH and shading affected behavioral responses of hermit crabs.
• Multiple stressors induced high mortality and reduced growth.
• Maintenance of local populations may be impaired by the impact of both stressors.

Abstract

Multiple simultaneous stressors induced by anthropogenic activities may amplify their impacts on marine organisms. The effects of ocean acidification, in combination with other anthropogenic impacts (apart from temperature) are poorly understood, especially in coastal regions. In these areas, shading caused by infrastructure development, such as harbor construction, may potentially interact with CO2-induced pH reduction and affect invertebrate populations. Here, we evaluated the effects of reduced pH (7.6) and shading (24h in darkness) on mortality, growth, calcification and displacement behavior to live predator (danger signal) and dead gastropod (resource availability signal) odors using juveniles of the hermit crab Pagurus criniticornis collected in Araçá Bay (São Paulo state, Southeastern Brazil). After a 98 day experimental period, both stressors had a significant interaction effect on mortality, and an additive effect on total growth. No difference in calcification was recorded among treatments, indicating that individuals were able to maintain calcification under reduced pH conditions. When exposed to odor of live predators, crab responses were only affected by shading. However, an interactive effect between both stressors was observed in response to gastropod odor, leading to reduced displacement behavior. This study shows how local disturbance impacts may enhance the effects of global environmental change on intertidal crustacean populations.

Continue reading ‘Vulnerability of juvenile hermit crabs to reduced seawater pH and shading’

Increased CO2 exacerbates the stress of ultraviolet radiation on photosystem II function in the diatom Thalassiosira weissflogii

Highlights

• Increased CO2 and UVR synergistically reduce photosystem II activity.
• Increased CO2 increases PsbA removal rate but reduces PsbD’s.
• Both increased CO2 and UVR enhance nonphotochemical quenching.
• Increased CO2 decreases the ratio of Rubisco large subunit (RbcL) to PsbA.

Abstract

Diatoms usually dominate phytoplankton community in coastal waters and experience rapid changes of underwater light. However, little is known regarding how increased CO2 would affect diatoms’ capacity in dealing with changing photosynthetically active radiation (PAR) and ultraviolet radiation (UVR). Here, we cultured a globally abundant diatom Thalassiosira weissflogii under two levels of CO2 (400, 1000 ppmv), and then analysed its PSII function during an increase in PAR and UVR to mimic an upward mixing event. UVR noticeably reduced photosystem II (PSII) activity (FV/FM) during the high light exposure, which was more significant for cells grown at the higher CO2 condition. The PsbA removal rate (KPsbA) was synergistically increased by high CO2 and UVR, while the PsbD removal rate (KPsbD) was decreased under higher CO2. Both CO2 and UVR had an inducible effect on sustained phase of nonphotochemical quenching (NPQs). The higher CO2 decreased the ratio of Rubisco large subunit (RbcL) to PsbA regardless of the radiation treatments. It seems that the increased NPQs and turnover of PsbA induced by higher CO2 were not enough to offset the stressful effect it brought about, particularly when higher CO2 was combined with UVR. These findings indicate that increased CO2 may exacerbate the harmful effect of UVR on PSII function in the T. weissflogii through reducing PsbD removal rate and the ratio of RbcL to PsbA during UVR exposure, and thus would affect its abundance and distribution in future ocean environment.

Continue reading ‘Increased CO2 exacerbates the stress of ultraviolet radiation on photosystem II function in the diatom Thalassiosira weissflogii’

The response of three Southern Ocean phytoplankton species to ocean acidification and light availability: a transcriptomic study

Ocean acidification (OA) and high light was found to negatively affect the Antarctic key species Phaeocystis antarctica, Fragilariopsis kerguelensis and Chaetoceros debilis. To unravel the underlying physiological response at the transcriptomic level, these species were grown under ambient and elevated pCO2 combined with low or high light. RNA sequencing revealed that the haptophyte was much more tolerant towards OA than the two diatoms as only these showed distinct OA-dependent gene regulation patterns. Under ambient pCO2, high light resulted in decreased glycolysis in P. antarctica. Contrastingly, upregulation of genes related to cell division and transcription as well as reduced expression of both cata- and anabolic carbon related pathways were seen in C. debilis. OA in combination with low light led to reduced respiration, but also surprisingly to higher expression of genes involved in light protection, transcription and translation in C. debilis. Though not affecting P. antarctica, OA combined with high light caused also photosensitivity in both diatoms. As additional response reallocation of carbon to lipids was found in C. debilis under these conditions. Overall, we conclude that P. antarctica is better adapted than the two diatoms to OA and high light.

Continue reading ‘The response of three Southern Ocean phytoplankton species to ocean acidification and light availability: a transcriptomic study’

Assessing the effects of climate change on Baltic Sea macroalgae – implications for the foundation species Fucus vesiculosus L.

Marine macroalgae are important foundation species on rocky shores. The large, habitat-forming species, in particular support a variety of associated flora and fauna. The Baltic Sea is naturally species-poor due to brackish water, and perennial, large macroalgae such as Fucus vesiculosus have high ecological importance and are characterized as foundation species in hard substrate bottoms. In the Baltic Sea, climate change has been predicted to result in elevated seawater temperatures, declining salinity, caused by increases in rainfall, coastal eutrophication and ocean acidification (OA). These changes may be harmful for macroalgae either directly or through interacting effects. This thesis investigates the potential effects of climate change on the Baltic macroalgae, focusing on the foundation species Fucus vesiculosus.

Continue reading ‘Assessing the effects of climate change on Baltic Sea macroalgae – implications for the foundation species Fucus vesiculosus L.’

Coral responses to temperature, irradiance and acidification stress: linking physiology to satellite remote sensing

The success of the symbiosis of scleractinian corals with dinoflagellates of the genus Symbiodinium is highly dependent on the availability of sufficient, but not excess, light for photosynthesis. After decades of fundamental research into the effect of light on the coral-dinoflagellate symbiosis, an important practical application is emerging in remote monitoring of bleaching at coral reefs. Coral bleaching that originates with the dysfunction of photosynthesis can be either photoacclimatory, a controlled adjustment in response to environmental change, or it can be associated with photodamage, an uncontrolled response to environmental change. It is the latter that tends to lead to severe bleaching events that decrease the rate of carbon fixation, generate excessive oxygen radicals and may ultimately lead to coral death if unfavourable conditions persist. Current best practice methods for the prediction of coral bleaching use water temperature as detected via satellite, and predict the onset of coral bleaching accurately, but not the percent of corals bleached at a reef or the extent of the ensuing mortality.

Continue reading ‘Coral responses to temperature, irradiance and acidification stress: linking physiology to satellite remote sensing’


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