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Marine Ecology Progress Series

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MEPS 412:29-44 (2010)  -  DOI:

Temporal and spatial variability of phytoplankton photosynthetic characteristics in a southern European estuary (Douro, Portugal)

Isabel C. Azevedo1,2,*, Pedro Duarte2,3, Adriano A. Bordalo1,2

1Laboratório de Hidrobiologia, Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto, Lg. Abel Salazar 2, 4099-003 Porto, Portugal
2Centro Interdisciplinar de Investigação Marinha e Ambiental (CIIMAR), Rua dos Bragas 289, 4050-123 Porto, Portugal
3Global Change, Energy, Environment and Bioengineering R & D Unit (CIAGEB), Faculdade de Ciências e Tecnologia, Universidade Fernando Pessoa, Praça 9 de Abril 349, 4249-004 Porto, Portugal

ABSTRACT: The timescales of variability in photosynthetic parameters and the relationships between environmental variables and photosynthetic response are important issues for an accurate estimation of phytoplankton primary production, a major feature of aquatic systems. In the present study, variability in phytoplankton photosynthetic parameters of the Douro estuary was analyzed using data from photosynthesis-irradiance (P-E) incubations performed during seasonal tidal cycles, as well as during monthly surveys carried out along a salinity gradient. Tidal surveys were conducted in October 2003 and January, May, and July 2004. Monthly surveys were conducted from December 2002 to December 2003. Diel variability in P-E parameters was highest during the summer survey. The highest values of the biomass-specific maximum photosynthetic rate Pmax were generally observed around noon or in the afternoon, and correlated positively with photosynthetic efficiency α. Seasonal variability in Pmax and α was mostly related to temperature and light, whereas photoacclimation seemed to be the most important factor in diel variability. Spatially, variability increased upstream for mean Pmax and α values, associated with higher chlorophyll a concentration and temperature. By combining a temperature-limiting function with the Steele P-E equation, 60% of Pmax variation was explained. Analysis of inter-seasonal, intra-seasonal, and diel variability of photosynthetic parameters suggests that, in the Douro, photosynthetic parameters Pmax and α are most variable at a seasonal timescale, while for optimal light intensity Eopt, diel variability was, as expected, highest. Thus, predictive models of primary productivity should take into account this seasonal variability when looking at larger timescales.

KEY WORDS: P-E parameters · Phytoplankton · Seasonal and diel variability · Primary production · River discharge · Douro estuary

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Cite this article as: Azevedo IC, Duarte P, Bordalo AA (2010) Temporal and spatial variability of phytoplankton photosynthetic characteristics in a southern European estuary (Douro, Portugal). Mar Ecol Prog Ser 412:29-44.

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