Elemental composition of suspended matter in the Scotia-Weddell Confluence area during spring and summer 1988 (EPOS Leg 2)

The effects of ambient solar UV radiation (280 to 400 nm) were determined using 3 natural marine protist communities incubated in 650 l tanks (minicosms) for 13 to 14 d over the summer of [2002][2003] at Davis Station, Antarctica. Minicosms were exposed to ambient light that was variously attenuated to give treatments of photosynthetically active radiation (PAR, ≥385 nm wavelength), PAR + UV-A radiation (315 to 385 nm), and PAR + UV-A + 4 different treatments of UV-B radiation (280 to 315 nm) that simulated a range of equivalent depths (ED) in the water column from 4.43 to 7.15 m. Results showed a seasonal progression in the response of microbial communities to UV radiation exposure. The first experiment in November showed that the microbial community was significantly inhibited in the PAR + UV-A-exposed treatment but this inhibition declined with increasing addition of UV-B radiation. The second experiment in December showed that UV-A or UV-B radiation had few significant effects. Like in Expt 1, some taxa were inhibited by PAR + UV-A or promoted by UV-B, but most were inhibited at the highest UV-B irradiances (≤4.43 m ED). The last experiment in January showed UV-B induced inhibition of all but one of the dominant taxa. The seasonal transition in UV wavelengths responsible for inhibition of protists may be due to ozone reduction, the light history of protists, and/or changes in species composition. The increasing UV-Binduced inhibition we observed over the summer corresponded to a decline in ozone concentrations over Davis. This recurrent decline in ozone over Antarctica between January and April coincides with blooms of diatoms that appear to have low UV-B tolerance but are responsible for ~47% of annual primary production in Antarctic waters. KEY WORDS: Antarctic · Marine protists · UV-A · UV-B · Ozone · Diatoms · Flagellates · Dinoflagellates Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 52: [131][132][133][134][135][136][137][138][139][140][141][142][143][144][145][146][147] 2008 due to the differing effectiveness of mechanisms to tolerate UV-B exposure, interspecific variation in UV-Binduced damage is reportedly high (e.g. Karentz et al. 1991). This has led to the suggestion that exposure to UV-B radiation may cause changes in the composition and abundance of marine protists with ramifications for trophodynamics and biogeochemical cycles (Laurion et al. 1998, Mostajir et al. 2000, Davidson & Belbin 2002, Sommaruga 2003.Remarkably few studies have addressed the effects of UV-B radiation on community-level interactions among marine microbes and fewer still have been performed in Antarctic waters (Davidson 2006). Some studies have shown that UV-B radiation has the potential to change the structure and function of Antarctic microbial communities (Smith et al. 1992, Davidson et al. 1996, Davidson & van der Heijden 2000, Davidson & Belbin 2002. However, as the results of community-level studies vary with environment, location and the composition of ...

Section: Methodsmentioning

confidence: 99%

Temporal changes in effects of ambient UV radiation on natural communities of Antarctic marine protists

Thomson¹,

Davidson²,

Cadman³

2008

“…The cell volumes were multiplied by 1.33 to compensate for cell shrinkage as a result of Lugol's fixation (Dehairs et al 1992); the cell carbon was calculated using the conversion statistics: 0.19 pg C μm -3 for ciliates (Putt & Stoeker 1989), 0.183 pg C μm -3 for heterotrophic dinoflagellates (Caron et al 1995), 0.22 pg C μm -3 for heterotrophic nanoflagellates (Børsheim & Bratak 1987) and pg C = 0.109 × (live cell volume) 0.991 for all other autotrophic and heterotrophic cells (Montagnes et al 1994). To minimise the number of variables (microbe species), the cell carbon concentrations attributable to each functional component of the microbial community (phytoplankton, protozoa and bacteria) were calculated, and the concentrations for each 10-min-integrated duration of exposure to UV were then determined (see below).…”

Section: Methodsmentioning

confidence: 99%

Modelled effects of ambient UV radiation on a natural Antarctic marine microbial community

Núñez¹,

Davidson²,

Michael³

2006

Ozone depletion over Antarctica has enhanced ultraviolet-B radiation (UVBR, 280 to 320 nm wavelength). We measured the effect of ambient solar UV radiation on the biomass and species composition of phytoplankton, protozoa, bacteria and dissolved organic carbon (DOC) in natural microbial assemblages from Antarctic coastal waters. Results were modelled to determine the features of the irradiance responsible for changes in the biomass of these microbial components and responses of individual phytoplankton taxa. Model results showed that changes in phytoplankton biomass were primarily due to dose rate, indicating that their UV-induced mortality resulted from the equilibrium between damage and repair. However, there was considerable variability between individual species in their response to dose and dose rate. Changes in protozoan biomass were mainly due to dose and were likely due to community-level, trophodynamic interactions. UV radiation did not measurably affect bacterial biomass, but resulted in increasing concentrations of DOC. We found a threshold of erythemal irradiance of 28 mW m -2 , approximating peak noon-time irradiance at 3.6 m depth near the summer solstice in Antarctic coastal waters, below which no change in the community structure was observed, but above which phytoplankton mortality and protozoan biomass increased. Our results indicate that enhanced UVB radiation in Antarctic waters increases phytoplankton mortality and causes changes in the structure, function and composition of the microbial community that are likely to return more photoassimilated carbon to the atmosphere. KEY WORDS: Antarctic · Model · UV · Ozone · Marine microbes Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 42: [75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90] 2006 pervasive, with molecular and cellular impacts on autotrophs flowing, via the food web, to cause changes on the ecosystem level (Vincent & Roy 1993). Most research on the effect of UV on marine microbes has focussed on its impact on phytoplankton (Davidson 1998). However, Bothwell et al. (1994) first showed that studies of UV-induced effects on single species or trophic levels could not be used to predict the impacts in natural communities, as they did not incorporate the effect of UV on trophic interactions. Recent studies show that UVB also directly impacts the production, growth, survival and species composition of bacteria, viruses and protozoa , Mostajir et al. 2000, Vernet 2000, increasing the likelihood that ecosystem-level changes will result from Antarctic ozone depletion. However, few studies have addressed UV-induced changes in the dynamics of natural marine microbial assemblages (Keller et al. 1997a,b, Wickham & Carstens 1998, Mostajir et al. 1999) and findings vary greatly. To our knowledge, no studies have been conducted in Antarctic marine waters other than those we have performed (Davidson & van der Heijden 2000, Davidson & Belbin 2002.Models can be used to better unde...

“…The cell volumes of each species were multiplied by 1.33 to compensate for cell shrinkage as a result of Lugol's fixation (Dehairs et al 1992). Cell carbon concentrations were calculated using the cell volume of each protist taxon and the following conversion statistics: 0.19 pg C µm -3 for ciliates (Putt & Stoeker 1989); 0.183 pg C µm -3 for heterotrophic dinoflagellates (Caron et al 1995); 0.22 pg C µm -3 for heterotrophic nanoflagellates (HNAN) (Børsheim & Bratak 1987); and pg C = 0.109 × (live cell volume) 0.991 for all other autotrophic and heterotrophic cells (Montagnes et al 1994).…”

Section: Methodsmentioning

confidence: 99%

Exposure of natural Antarctic marine microbial assemblages to ambient UV radiation: effects on the marine microbial community

Davidson¹,

Belbin²

2002

The effect of ambient solar UV radiation on natural protist (phytoplankton and protozoan) assemblages from Antarctic coastal waters was determined. Subsamples of the community were exposed to UV radiation attenuated to equivalent water column depths (ED) of 1.0, 2.0, 3.0, 3.6 and ≥ 20 m for periods of between 8 h and 1 wk. Total concentrations of phytoplankton in treatments exposed at 3.0 and 3.6 m ED were similar to those in control treatments. However, exposure of phytoplankton at ≤ 2.0 m ED for ≥1 d reduced overall cell size, concentration and biomass. Following UV exposure, some species of phytoplankton died, some flourished and others were unaffected. In contrast, the total concentrations of protozoans at ≤ 2.0 m ED for ≥1 d were commonly higher than in controls, and 2-to 3-fold higher than at 3.0 and 3.6 m ED. Significant negative correlation was observed between the total concentrations of phytoplankton and protozoa, showing that UV-induced mortality of phytoplankton resulted, directly or indirectly, in an increase in the concentrations of protozoans. Our results showed that UV radiation can change the biomass and species composition of marine microbial communities, altering size and availability of food for higher trophic levels and changing their trophic structure. Thus, increased UVB as a result of ozone depletion is likely to change food web structure and function and may influence biogeochemical cycles.