MEPS 206:87-95 (2000)  -  doi:10.3354/meps206087

Effect of nutrient supply on the biomass structure of planktonic communities: an experimental test on a Mediterranean coastal community

Carlos M. Duarte1,*, Susana Agustí1, Josep M. Gasol2, Dolors Vaqué2, Evaristo Vazquez-Dominguez2

1Instituto Mediterráneo de Estudios Avanzados (IMEDEA), CSIC-Universitat de les Illes Balears, c/ Miguel Marqués, 21, 07190 Esporles (Mallorca), Spain
2Institut de Ciencies del Mar, CSIC, Passeig Joan de Borbó s/n, 08039 Barcelona, Spain

ABSTRACT: The hypothesis that increasing nutrient supply increases the biomass of autotrophs proportionately more than the biomass of heterotrophs was tested by increasing (0, 1-, 2-, 4-, 8-, and 16-fold over the background loading of 5 mmol N m-2 d-1, 1.6 mmol Si m-2 d-1, and 0.25 mmol P m-2 d-1) the addition of nutrients to large (33000 l) mesocosm units enclosing an oligotrophic coastal Mediterranean planktonic community. Autotrophic plankton biomass increased 50-fold along the range of nutrient inputs, whereas heterotrophic biomass increased only 10-fold. Heterotrophic biomass increased as the 1Ž5 power of the increase in the biomass of autotrophs, implying that the ratio of heterotroph to autotroph biomass (HB/AB ratio) declined rapidly as the biomass of autotrophs increases with increasing nutrient inputs. The biomass distribution within the community shifted from an Œinverted pyramid¹ distribution, involving gr