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Marine Ecology Progress Series

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MEPS 399:27-37 (2010)  -  DOI:

Synechococcus and Prochlorococcus cell death induced by UV radiation and the penetration of lethal UVR in the Mediterranean Sea

Moira Llabrés1,*, Susana Agustí1, Patricia Alonso-Laita1, Gerhard J. Herndl2,3

1Department of Global Change Research, IMEDEA (CSIC-UIB) Instituto Mediterráneo de Estudios Avanzados, Miquel Marqués 21, 07190 Esporles, Mallorca, Spain
2Department of Biological Oceanography, Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands
3Department of Marine Biology, University of Vienna, Vienna Ecology Center, Althanstr. 14, 1090 Vienna, Austria

ABSTRACT: Irradiation experiments performed on natural communities of picocyanobacteria from the southwest Mediterranean Sea indicated that natural levels of solar ultraviolet radiation (UVR: 280 to 400 nm) induced important cell death in Prochlorococcus sp., although Synechococcus sp. appeared to be highly resistant. In the treatments where UVB radiation (UVBR, 280 to 315 nm) was excluded, Prochlorococcus also experienced high cell death with short half-life times of 3.01 ± 0.1 SE (h), showing the contribution of UVA radiation (UVAR, 315 to 400 nm) and photosynthetically active radiation (PAR, 400 to 700 nm) to Prochlorococcus cell death. Underwater radiometric measurements conducted during the cruise indicated that penetration of UVR was significant in the Mediterranean waters studied, with minimum diffuse attenuation coefficients of 0.165 and 0.071 m–1 for 313 and 380 nm, respectively. The lethal UV doses required to decrease the picocyanobacteria populations by half, UVLRD50, calculated experimentally, were related to underwater UVR penetration in the Mediterranean Sea measured during the cruise. By calculating (from incident irradiances and UVR penetration) the daily UV doses at different depths in the water column, we found that, for sunny days, experimental Prochlorococcus LRD50 (187 kJ m–2) could reach from 10 to 26 m depth. For Synechococcus, however, the depth receiving daily UVLRD50 (1375 kJ m–2) was always shallower, above 5 m depth. The differential sensitivity of the 2 genera and the UV transparency of the Mediterranean Sea suggest that solar radiation could be an important factor influencing the dynamics and distribution of cyanobacterial populations in the surface waters of this oligotrophic sea.

KEY WORDS: Prochlorococcus · Synechococcus · Mediterranean Sea · UV radiation · Cell death · UV penetration · Diffuse attenuation coefficient · UVLRD50

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Cite this article as: Llabrés M, Agustí S, Alonso-Laita P, Herndl GJ (2010) Synechococcus and Prochlorococcus cell death induced by UV radiation and the penetration of lethal UVR in the Mediterranean Sea. Mar Ecol Prog Ser 399:27-37.

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