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Marine Ecology Progress Series

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MEPS 416:17-33 (2010)  -  DOI:

Differential responses of phytoplankton and heterotrophic bacteria to organic and inorganic nutrient additions in coastal waters off the NW Iberian Peninsula

Sandra Martínez-García1,*, Emilio Fernández1, Xosé-Antón Álvarez-Salgado2, Jose González1, Christian Lønborg2,3, Emilio Marañón1, Xosé-Anxelu G. Morán4, Eva Teira1

1Departamento Ecoloxía e Bioloxía Animal, Universidade de Vigo, Campus Lagoas-Marcosende, 36310 Vigo, Spain
2CSIC, Insituto de Investigacións Mariñas, Eduardo Cabello 6, 36208 Vigo, Spain
3Scottish Association for Marine Science, Oban, Argyll PA37 1QA, UK
4Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Camín de L’Arbeyal s/n, 33212 Xixón, Spain

ABSTRACT: The short-term effects of inorganic N and P (nitrate, ammonium, phosphate) and organic C and N (glucose, amino acids) input, added separately as well as jointly, on microplankton community structure and metabolism were studied in 6 microcosm experiments conducted from February to July 2008 in a eutrophic coastal embayment in NW Spain under contrasting hydrographic conditions. The responses of planktonic communities were highly variable. Strong positive effects of combined inorganic and organic nutrient enrichments for phytoplankton and heterotrophic bacteria were found. In most experiments enhanced phytoplankton biomass and productivity (primary production increased up to 5.5-fold) was measured after mixed (inorganic plus organic) additions but phytoplankton responded only in one of the experiments after inorganic additions. Heterotrophic bacteria responded faster than phytoplankton to the additions but were never affected by inorganic nutrient additions, suggesting a C limitation of bacterial activity in this coastal environment. Heterotrophic bacteria biomass, productivity, and respiration responded to mixed additions (containing C, N, and P) in all the experiments (bacterial production increased from 14- to 34-fold) whereas its response to organic (containing C and N) additions greatly differed among experiments (bacterial production increased from 0.6- to 21-fold), which could be partially related to P availability. A general increase in bacterial growth efficiency occurred only after mixed additions (up to 2-fold). The tendency towards heterotrophy of the microbial plankton community was weaker after the mixed (Production/Respiration (P/R) ratio changes from 0.34- to 1.6-fold) than after the organic additions (P/R changes from 0.16- to 0.8-fold). Our results suggest that phytoplankton requirememnts for organic nutrients for growth and P deficiency of bacterial populations intermittently occur in this coastal area.

KEY WORDS: Nutrient additions · Organic nitrogen · Phytoplankton · Bacteria

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Cite this article as: Martínez-García S, Fernández E, Álvarez-Salgado XA, González J and others (2010) Differential responses of phytoplankton and heterotrophic bacteria to organic and inorganic nutrient additions in coastal waters off the NW Iberian Peninsula. Mar Ecol Prog Ser 416:17-33.

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