No adaptation to warming after selection for 800 generations in the coccolithophore Emiliania huxleyi BOF 92

Ocean warming is suggested to exert profound effects on phytoplankton physiology and growth. Here, we investigated how the coccolithophore Emiliania huxleyi (BOF 92, a non-calcifying strain) responded to changes in temperature in short- and long-term thermal treatments. The specific growth rate after 10 days of acclimation increased gradually with increasing temperatures (14, 17, 21, 24, 28°C) and peaked at ~23°C, followed by a significant decrease to 28°C. Chlorophyll a content, cell size, photosynthetic rate, and respiratory rate increased significantly from 14°C to 24°C, but the cellular particulate organic carbon (POC) and nitrogen (PON) showed the lowest values at the optimal temperature. In contrast, during long-term thermal treatments at 17°C and 21°C for 656 days (~790 generations for 17°C treatment; ~830 generations for 21°C treatment), the warming significantly stimulated the growth in the first 34 days and the last 162 days, but there was no significant difference in specific growth rate from Day 35 to Day 493. Chlorophyll a content, cell size, cellular POC/PON, and the ratio of POC to PON, showed no significant difference between the warming and control for most of the duration of the long-term exposure. The warming-selected population did not acquire persistent traits in terms of growth and cell quotas of POC and PON, which resumed to the levels in the control temperature treatment after about 9 generations in the shift test. In summary, our results indicate that warming by 4°C (17°C and 21°C) enhanced the growth, but did not result in adaptative changes in E. huxleyi (BOF 92) over a growth period of about 800 generations, reflecting that mild or non-stressful warming treatment to E. huxleyi isolated from cold seas does not alter its phenotypic plasticity

Solar UV Radiation Drives CO 2 Fixation in Marine Phytoplankton: A Double-Edged Sword

Photosynthesis by phytoplankton cells in aquatic environmentscontributes to more than 40% of the globalprimary production (Behrenfeld et al., 2006). Withinthe euphotic zone (down to 1% of surface photosyntheticallyactive radiation [PAR]), cells are exposed notonly to PAR (400–700 nm) but also to UV radiation(UVR; 280–400 nm) that can penetrate to considerabledepths (Hargreaves, 2003). In contrast to PAR, which isenergizing to photosynthesis, UVR is usually regardedas a stressor (Ha¨der, 2003) and suggested to affect CO2-concentrating mechanisms in phytoplankton (Beardallet al., 2002). Solar UVR is known to reduce photosyntheticrates (Steemann Nielsen, 1964; Helbling et al.,2003), and damage cellular components such as D1proteins (Sass et al., 1997) and DNA molecules (Bumaet al., 2003). It can also decrease the growth (Villafan˜ eet al., 2003) and alter the rate of nutrient uptake(Fauchot et al., 2000) and the fatty acid composition(Goes et al., 1994) of phytoplankton. Recently, it hasbeen found that natural levels of UVR can alter themorphology of the cyanobacterium Arthrospira (Spirulina)platensis (Wu et al., 2005b).On the other hand, positive effects of UVR, especiallyof UV-A (315–400 nm), have also been reported.UV-A enhances carbon fixation of phytoplankton underreduced (Nilawati et al., 1997; Barbieri et al., 2002)or fast-fluctuating (Helbling et al., 2003) solar irradianceand allows photorepair of UV-B-induced DNAdamage (Buma et al., 2003). Furthermore, the presenceof UV-A resulted in higher biomass production of A.platensis as compared to that under PAR alone (Wuet al., 2005a). Energy of UVR absorbed by the diatomPseudo-nitzschia multiseries was found to cause fluorescence(Orellana et al., 2004). In addition, fluorescentpigments in corals and their algal symbiont are knownto absorb UVR and play positive roles for the symbioticphotosynthesis and photoprotection (Schlichter et al.,1986; Salih et al., 2000). However, despite the positiveeffects that solar UVR may have on aquatic photosyntheticorganisms, there is no direct evidence to whatextent and howUVR per se is utilized by phytoplankton.In addition, estimations of aquatic biological productionhave been carried out in incubations consideringonly PAR (i.e. using UV-opaque vials made of glass orpolycarbonate; Donk et al., 2001) without UVR beingconsidered (Hein and Sand-Jensen, 1997; Schippersand Lu¨ rling, 2004). Here, we have found that UVR canact as an additional source of energy for photosynthesisin tropical marine phytoplankton, though it occasionallycauses photoinhibition at high PAR levels. WhileUVR is usually thought of as damaging, our resultsindicate that UVR can enhance primary production ofphytoplankton. Therefore, oceanic carbon fixation estimatesmay be underestimated by a large percentageif UVR is not taken into account.Fil: Gao, Kunshan. Shantou University; ChinaFil: Wu, Yaping. Xiamen University; ChinaFil: Villafañe, Virginia Estela. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Helbling, Eduardo Walter. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Enhanced calcification ameliorates the negative effects of UV radiation on photosynthesis in the calcifying phytoplankter Emiliania huxleyi

The calcifying phytoplankton species, coccolithophores, have their calcified coccoliths around the cells, however, their physiological roles are still unknown. Here, we hypothesized that the coccoliths may play a certain role in reducing solar UV radiation (UVR, 280-400 nm) and protect the cells from being harmed. Cells of Emiliania huxleyi with different thicknesses of the coccoliths were obtained by culturing them at different levels of dissolved inorganic carbon and their photophysiological responses to UVR were investigated. Although increased dissolved inorganic carbon decreased the specific growth rate, the increased coccolith thickness significantly ameliorated the photoinhibition of PSII photochemical efficiency caused by UVR. Increase by 91% in the coccolith thickness led to 35% increase of the PSII yield and 22% decrease of the photoinhibition of the effective quantum yield (I broken vertical bar(PSII)) by UVR. The coccolith cover reduced more UVA (320-400 nm) than UVB (280-315 nm), leading to less inhibition per energy at the UV-A band.National Basic Research Program of China [2009CB421207]; National Natural Science Foundation of China [40930846, 40676063]; MEL Young Scientist Visiting Fellowship ; Xiamen University and Ph. D. Foundation of Wenzhou Medical College [MELRS0935, 89209008

Combined effects of CO 2 level, light intensity, and nutrient availability on the coccolithophore Emiliania huxleyi

Abstract(#br)Continuous accumulation of fossil CO 2 in the atmosphere and increasingly dissolved CO 2 in seawater leads to ocean acidification (OA), which is known to affect phytoplankton physiology directly and/or indirectly. Since increasing attention has been paid to the effects of OA under the influences of multiple drivers, in this study, we investigated effects of elevated CO 2 concentration under different levels of light and nutrients on growth rate, particulate organic (POC) and inorganic (PIC) carbon quotas of the coccolithophorid Emiliania huxleyi . We found that OA treatment (pH 7.84, CO 2 = 920 μatm) reduced the maximum growth rate at all levels of the nutrients tested, and exacerbated photo-inhibition of growth rate under reduced availability of phosphate (from 10.5 to 0.4..

High levels of solar radiation offset impacts of ocean acidification on calcifying and non-calcifying strains of Emiliania huxleyi

Coccolithophores, a globally distributed group of marine phytoplankton, showed diverse responses to ocean acidification (OA) and to combinations of OA with other environmental factors. While their growth can be enhanced and calcification be hindered by OA under constant indoor light, fluctuation of solar radiation with ultraviolet irradiances might offset such effects. In this study, when a calcifying and a non-calcifying strain of Emiliania huxleyi were grown at 2 CO2 concentrations (low CO2 [LC]: 395 µatm; high CO2 [HC]: 1000 µatm) under different levels of incident solar radiation in the presence of ultraviolet radiation (UVR), HC and increased levels of solar radiation acted synergistically to enhance the growth in the calcifying strain but not in the non-calcifying strain. HC enhanced the particulate organic carbon (POC) and nitrogen (PON) productions in both strains, and this effect was more obvious at high levels of solar radiation. While HC decreased calcification at low solar radiation levels, it did not cause a significant effect at high levels of solar radiation, implying that a sufficient supply of light energy can offset the impact of OA on the calcifying strain. Our data suggest that increased light exposure, which is predicted to happen with shoaling of the upper mixing layer due to progressive warming, could counteract the impact of OA on coccolithophores distributed within this layer

Ocean acidification increases the accumulation of toxic phenolic compounds across trophic levels

Increasing atmospheric CO2 concentrations are causing ocean acidification (OA), altering carbonate chemistry with consequences for marine organisms. Here we show that OA increases by 46–212% the production of phenolic compounds in phytoplankton grown under the elevated CO2 concentrations projected for the end of this century, compared with the ambient CO2 level. At the same time, mitochondrial respiration rate is enhanced under elevated CO2 concentrations by 130–160% in a single species or mixed phytoplankton assemblage. When fed with phytoplankton cells grown under OA, zooplankton assemblages have significantly higher phenolic compound content, by about 28–48%. The functional consequences of the increased accumulation of toxic phenolic compounds in primary and secondary producers have the potential to have profound consequences for marine ecosystem and seafood quality, with the possibility that fishery industries could be influenced as a result of progressive ocean change

Reviews and Syntheses: Ocean acidification and its potential impacts on marine ecosystems

Ocean acidification, a complex phenomenon that lowers seawater pH, is the net outcome of several contributions. They include the dissolution of increasing atmospheric CO2 that adds up with dissolved inorganic carbon (dissolved CO2, H2CO3, HCO3−, and CO32−) generated upon mineralization of primary producers (PP) and dissolved organic matter (DOM). The aquatic processes leading to inorganic carbon are substantially affected by increased DOM and nutrients via terrestrial runoff, acidic rainfall, increased PP and algal blooms, nitrification, denitrification, sulfate reduction, global warming (GW), and by atmospheric CO2 itself through enhanced photosynthesis. They are consecutively associated with enhanced ocean acidification, hypoxia in acidified deeper seawater, pathogens, algal toxins, oxidative stress by reactive oxygen species, and thermal stress caused by longer stratification periods as an effect of GW. We discuss the mechanistic insights into the aforementioned processes and pH changes, with particular focus on processes taking place with different timescales (including the diurnal one) in surface and subsurface seawater. This review also discusses these collective influences to assess their potential detrimental effects to marine organisms, and of ecosystem processes and services. Our review of the effects operating in synergy with ocean acidification will provide a broad insight into the potential impact of acidification itself on biological processes. The foreseen danger to marine organisms by acidification is in fact expected to be amplified by several concurrent and interacting phenomena