Influence of water mixing on the inhibitory effect of UV radiation on primary and bacterial production in Mediterranean coastal water
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The scaling of the solar ultraviolet radiation (UVR, 280–400 nm) effect on phyto- and bacterio-plankton at the ecosystem level is difficult since its estimate is often based on short-time incubation experiments performed at fixed depths, neglecting the previous days’ radiation history and the variable radiation caused by vertical mixing. To examine this issue, we measured primary (PP) and bacterial (BP) production in samples from coastal water in the Northwest Mediterranean Sea incubated at fixed depths or moving vertically within the water column (0–8 m) with a periodicity of 22 min, exposed to full sun, PAR or maintained in dark. Three experiments were carried out on consecutive days to measure day-to-day variations in planktonic response. In surface waters, PP was inhibited by ~32 to 42% by UVR, and BP was inhibited by ~50 to 70% by solar radiation (UVR + PAR). We observed a general decrease in the integrated inhibition of PP due to UVR for both fixed and moving incubations over the 3 days from ~27% of inhibition to non-significant inhibition. In contrast, large discrepancies were observed in the integrated inhibition of BP due to solar radiation (UVR + PAR) between fixed and moving incubations. Whereas both type of incubations gave similar estimation of solar radiation inhibition on day 1 (~25%), inhibition became much higher for fixed incubation compared to moving incubation on days 2 and 3. Differences in responses between days suggest that light history, spectral quality, photoadaptation or acclimation may be important factors in daily observed responses. Our results also underline, for the first time, the importance of the vertical mixing in the BP inhibition by solar radiation.
KeywordsPrimary production Bacterial production Mediterranean sea Ultraviolet radiation Vertical mixing
We thank the crew of the Service d’Observation du Laboratoire Arago for their assistance during field sampling and incubation. We also acknowledge Météo France for the release of the wind speed data and E. Balseiro for revising the early version of the manuscript. This study was funded by the CNRS-PROOF program (“Induction of microbial community responses and dissolved organic matter transformation by UltraViolet radiation in marine ECOsystems” [UVECO] project) and by National Science Foundation Office of International Science and Engineering U.S-France Cooperative Science Program grant 0340764 to W.H.J.
- Abboudi M, Jeffrey WH, Ghiglione J-F, Pujo-Pay M, Oriol L, Sempéré R, Charrière B, Joux F (2008) Effects of photochemical transformations of dissolved organic matter on bacterial metabolism and diversity in three contrasting coastal sites in the Northwestern Mediterranean Sea during summer. Microb Ecol 55:344–357PubMedCrossRefGoogle Scholar
- Booth MG, Hutchinson L, Brumsted M, Aas P, Coffin RB, Downer RC, Kelley CA, Lyons MM, Pakulski JD, Sandvik SLH, Jeffrey WH, Miller RV (2001) Quantification of recA expression as an indicator of repair potential in marine bacterioplankton communities of Antarctica. Aquat Microb Ecol 24:51–59CrossRefGoogle Scholar
- Joux F, Jeffrey WH, Abboudi M, Pujo-Pay M, Oriol L, Neveux J, Naudin J-J (2009) Ultraviolet radiation in the Rhone lenses of low salinity and marine waters of the northwestern Mediterranean Sea: attenuation and effects on bacterial production and net community production. Photochem Photobiol 85:783–793PubMedCrossRefGoogle Scholar
- Kirchman DL (1993) Leucine incorporation as a measure of biomass production by heterotrophic bacteria. In: Kemp PF (ed) Handbook of methods in aquatic microbial ecology. Lewis Publishers, Boca Raton, pp 509–512Google Scholar
- Smith DC, Azam F (1992) A simple, economical method for measuring bacterial protein synthesis rates in seawater using 3H-leucine. Mar Microb Food Webs 6:107–114Google Scholar
- Steeman-Nielsen E (1952) The use of radioactive carbon for measuring organic production in the sea. J Cons Int Explor Mer 18:117–140Google Scholar
- Tréguer P, Le Corre P (1975) Manuel d’analyse des sels nutritifs dans l’eau de mer. Utilisation de l’Autoanalyzer II Technicon. 2nd édn. Laboratoire d’Océanographie chimique, Université de Bretagne Occidentale, Brest FranceGoogle Scholar