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Marine Ecology Progress Series

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MEPS 489:93-105 (2013)  -  DOI:

Water nutrient stoichiometry modifies the nutritional quality of phytoplankton and somatic growth of crustacean mesozooplankton

Beatriz Díez1,2,*, Lies Van Nieuwerburgh3, Pauline Snoeijs4

1Department of Botany, Stockholm University, 10691 Stockholm, Sweden
2Department of Molecular Genetic and Microbiology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, C.P. 651 3677, Santiago, Chile
3Royal Haskoning DHV, 9702 KB Groningen, The Netherlands
4Department of Ecology, Environment and Plant Sciences, Stockholm University, 10691 Stockholm, Sweden

ABSTRACT: Here, we investigated how changes in water nutrient stoichiometry may change the nutritional quality of phytoplankton for mesozooplankton. For 6 d, we added nutrients to nine 1300 l mesocosms with natural summer phytoplankton from the Baltic Sea to create communities that were N-limited (P‑treatment), Si-limited (PN-treatment) and not limited by nutients (PNSi-treatment). With the addition of P, no major changes occurred in phytoplankton biomass or species composition with time. With the addition of P and N, with or without excess of Si, C:N ratios approached the Redfield ratio, biomass increased and diatoms and dinoflagellates became dominant. Analysis of the 18S rRNA gene showed that the availability and diversity of phytoplankton other than diatoms and dinoflagellates, like prasinophytes or heterotrophic flagellates and ciliates, were not affected by the nutrient treatments. We then tested how the modified phytoplankton communities affected somatic growth in a natural mesozooplankton community dominated by the copepod genus Acartia. After 6 d of grazing, the zooplankton more than doubled their C content per individual when grazing on the Si-limited phytoplankton (PN-treatment) while total community biomass was maintained. In the other 2 treatments, the C content per individual remained the same and total community biomass decreased by ca. 60%, which suggests that the zooplankton was not optimally fed. Thus, a phytoplankton community with stoichiometry close to the Redfield ratio provided the best nutritional quality for the zooplankton, but not when the diatoms were Sisaturated. This study shows that nutrient stoichiometry in the seawater can affect zooplankton growth by modification of the phytoplankton community. It also shows that the food quality of phytoplankton does not depend only on the taxonomic composition, but also on the nutrient stoichiometry.

KEY WORDS: Eutrophication · Phytoplankton · Grazing · Mesozooplankton · Mesocosm experiment · Pigment composition · 18S rRNA gene

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Cite this article as: Díez B, Van Nieuwerburgh L, Snoeijs P (2013) Water nutrient stoichiometry modifies the nutritional quality of phytoplankton and somatic growth of crustacean mesozooplankton. Mar Ecol Prog Ser 489:93-105.

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