MEPS 297:51-60 (2005)  -  doi:10.3354/meps297051

Large-sized phytoplankton sustain higher carbon-specific photosynthesis than smaller cells in a coastal eutrophic ecosystem

Pedro Cermeño1,*, Emilio Marañón1, Jaime Rodríguez2, Emilio Fernández1

1Departamento de Ecología y Biología Animal, Facultad de Ciencias del Mar, Universidad de Vigo, 36310 Vigo, Spain
2Departamento de Ecología y Geología, Universidad de Málaga, Campus de Teatinos, 29071 Málaga, Spain

ABSTRACT: Size-fractionated, carbon-specific photosynthesis by natural phytoplankton assemblages has been analysed during a full annual cycle in a coastal, productive ecosystem. We observed high variability in the carbon-specific photosynthetic rates by the different phytoplankton size fractions. In surface waters, under high irradiance levels, large-sized phytoplankton showed consistently higher carbon-specific photosynthetic rates than small-sized cells. We suggest the possibility that interspecific differences in acquisition and use of light and nutrients account for this pattern. Under light-limited conditions at the bottom of the euphotic layer, differences in the carbon-specific photosynthesis between size fractions were lower or disappeared, which was likely due to the package effect on larger cells. Our results show that when the whole phytoplankton community is analysed, the relationship between carbon-specific photosynthesis and cell size is variable. Moreover, a higher carbon-specific photosynthesis by larger phytoplankton might represent an ecophysiological basis to explain their dominance in resource-rich environments.

KEY WORDS: Phytoplankton · Cell size · Carbon-specific photosynthesis · Eutrophic ecosystem

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