VILLAFAÑE virginia Estela
Photosynthesis vs. irradiance characteristics in phytoplankton assemblages off Patagonia (Argentina): Temporal variability and solar UVR effects
VIRGINIA ESTELA VILLAFAÑE; M ALEJANDRA MARCOVAL; E WALTER HELBLING
MARINE ECOLOGY PROGRESS SERIES
Año: 2004 vol. 284 p. 23 - 34
From November 2002 to June 2003, we carried out experiments to determine the temporal variability of P vs. E curves and the effects of solar ultraviolet radiation (UVR, 280400 nm) on photosynthetic parameters of natural phytoplankton assemblages from Patagonia. Samples were collected at 2 sites, Bahía Nueva and Bahía Camarones (Chubut, Argentina), and exposed to solar radiation for 4 to 6 h under 3 quality radiation treatments (i.e. PAR + UVR, 280700 nm; PAR + UV-A, 320700 nm; and PAR only, 400700 nm), and under 6 to 8 levels of ambient irradiance (i.e. by using 0 to 57 layers of neutral density screens). Samples collected at Bahía Nueva had relatively high Pmax values (~34 μg C (μg chl a)1 h1) during the pre bloom period (i.e. late summer to late fall) and relatively low values (~1.52.5 μg C (μg chl a)1 h1) during the post-bloom period (i.e. late spring to early summer); similar results were observed in samples collected at Bahía Camarones. The light saturation parameter Ek, on the other hand, did not show a clear pattern and values ranging from 50 to 400 μmol m2 s1 were observed throughout the study period. High Pmax values were significantly correlated with the concentration of large diatoms (R2 = 0.6, p < 0.05), the taxonomic group that characterized the pre-bloom period. UVR significantly reduced Pmax values (p < 0.05) during the prebloom but not during the post-bloom period. UVR also significantly affected Ek (p < 0.05) in all Bahía Camarones samples but only in some from Bahía Nueva. UV-A was responsible for the bulk ofphotosynthetic inhibition throughout the study period; the highest UV-A-induced integrated inhibition values in the water column were ~16.5 and 7% for Bahía Nueva and Bahía Camarones, respectively. On the other hand, UV-B-induced photosynthetic inhibition reached maximum values of 2.3 and 3.9% for Bahía Nueva and Bahía Camarones, respectively. Since under certain environmental conditions P vs. E parameters can be significantly reduced by UVR, we suggest that remote sensing algorithms using these parameters should also consider the impact of UVR in their estimates of primary production.