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

Interactions of anthropogenic stress factors on marine phytoplankton

Phytoplankton are the main primary producers in aquatic ecosystems. Their biomass production and CO2 sequestration equals that of all terrestrial plants taken together. Phytoplankton productivity is controlled by a number of environmental factors, many of which currently undergo substantial changes due to anthropogenic global climate change. Most of these factors interact either additively or synergistically. Light availability is an absolute requirement for photosynthesis, but excessive visible and UV radiation impair productivity. Increasing temperatures enhance stratification and decrease the depth of the upper mixing layer exposing the cells to higher solar radiation and reduce nutrient upward transport from upwelling deeper water. At the same time, stratospheric ozone depletion exposes phytoplankton to higher solar UV-B radiation especially in polar and mid-latitudes. Terrestrial runoff carrying sediments and dissolved organic matter into coastal waters leads to eutrophication while reducing UV penetration. All these environmental forcings are known to affect physiological and ecological processes. Ocean acidification due to increased atmospheric CO2 concentrations changes the seawater chemistry; it reduces calcification in phytoplankton, macroalgae and many zoological taxa. Ocean warming results in changing species composition and favors blooms of toxic prokaryotic and eukaryotic phytoplankton. Increasing pollution from crude oil spills, persistent organic pollutants, heavy metal as well as industrial and household wastewaters affect phytoplankton which is augmented by solar UV radiation. Extensive analyses of the impacts of multiple stressors are scarce. Here, we review reported findings on the impacts of anthropogenic stressors on phytoplankton with an emphasis on their interactive effects and make an effort to provide a prospect for future studies

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

Ocean deoxygenation dampens resistance of diatoms to ocean acidification in darkness

Respiratory activity in the oceans is declining due to the expansion of hypoxic zones and progressive deoxygenation, posing threats to marine organisms along with impacts of concurrent ocean acidification. Therefore, understanding the combined impacts of reduced pO2 and elevated pCO2 on marine primary producers is of considerable significance. Here, to simulate diatoms’ sinking into the aphotic zone of turbid coastal water, we exposed the diatoms Thalassiosira pseudonana and Thalassiosira weissflogii in darkness at 20°C to different levels of pO2 and pCO2 conditions for ~3 weeks, and monitored their biomass density, photosynthetic activity and dark respiration, and examined their recovery upon subsequent exposure to light at 20°C, simulating surface water conditions. Along with decreased cell abundance and size, measured photosynthetic capacity and dark respiration rates in these two diatoms both gradually decreased during the prolonged darkness. Reduced pO2 alone did not negatively affect the photosynthetic machinery in both the dark-survived diatom, and enhanced their subsequent recovery upon light exposure. Nevertheless, the combination of the elevated pCO2 and reduced pO2 (equivalent to hypoxia) led to the biomass loss by about 90% in T. pseudonana, and delayed the recovery of both species upon subsequent exposure to light, though it did not reduce the cell concentration of T. weissflogii during the elongated darkness. Our results suggest that reduced O2 availability diminishes the abilities of the diatoms to cope with the acidic stress associated with ocean acidification, and the expansion of hypoxic waters could delay the photosynthetic recovery of coastal diatoms when they are transported upwards through mixing from dark layers to sunlit waters

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