Nutrient accumulation at different supply rates in experimental Mediterranean planktonic communities

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 207:1-11 (2000) - doi:10.3354/meps207001 Nutrient accumulation at different supply rates in experimental Mediterranean planktonic communities Montserrat Vidal*, Carlos M. Duarte Instituto Mediterráneo de Estudios Avanzados (IMEDEA), CSIC - Universitat de les Illes Balears, Miquel Marqués 21, 07190 Esporles (Mallorca, Islas Baleares), Spain *Present address: Laboratoire d¹Océanographie Biologique- UMR 7621, Laboratoire Arago, BP 44, 66651 Banyuls-sur-Mer Cedex, France. E-mail: mvidal@arago.obs-banyuls.fr ABSTRACT: A mesocosm experiment was conducted between June 18 and July 8, 1997, in the Bay of Blanes (NE Spain) to test for the effect of nutrient inputs on Mediterranean plankton communities. The experiment involved a gradient of daily nutrient additions to mesocosms (14 m high, 4.2 m2 cross-sectional area and 33 m3 effective volume), which were scaled to the nutrient loading of the Bay of Blanes in summer (0.64 µM N d-1, referred to as the Œbusiness as usual¹ control). This paper deals with the accumulation of nutrients in different size components (0.2-2, 2-20 and 20-200 µm) of the community and the efficiency with which these size components retain the added nutrients. Summer Mediterranean plankton responded significantly to nutrient additions by increasing their biomass, up to more than 100-fold that initially present in the enclosed water, and by changing the community structure, from an initial dominance of picoplankton to increased dominance of the 2-20 µm size component of the community (which contributes to more than 90% of the accumulated N and P) as the nutrient load increased. Though the initial community was able to accumulate nutrients exceeding the already high summer loading of the Bay of Blanes and thus acted as strong nitrogen (N) and phosphorus (P) sink, it was unable to trap the nutrients above a certain threshold: 4-fold (for N) and 8-fold (for P) the Œbusiness as usual¹ load. Conspicuous biomass increases were most noticeable after the nutrient inputs were increased 16-fold that value. Nevertheless, the biomass response was relatively low and involved a low efficiency (8%) in the trapping of added nutrients. As efficiencies were transiently higher (of 50% or even greater, between consecutive sampling days) we suggest factors other than a low assimilation by osmotrophs as responsible for the resilience of the plankton community for the trapping of nutrients in biomass in response to nutrient additions. The tendency of a lower biomass response to nutrient additions in the warm oligotrophic Mediterranean waters than in more eutrophic waters, if confirmed, should have profound consequences concerning the management of the coastline and the delineation of critical nutrient loadings. KEY WORDS: Nutrient accumulation · Coastal plankton · Size structure · Eutrophication · Mesocosm · NW Mediterranean Sea Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 207. Online publication date: November 22, 2000 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2000 Inter-Research.