Stimulation of metazooplankton by photochemically modified dissolved organic matter

Daniel, Cesar, Wilhelm Granéli, Emma S. Kritzberg, Alexandre M. Anesio

Limnol. Oceanogr., 51(1), 2006, 101-108 | DOI: 10.4319/lo.2006.51.1.0101

ABSTRACT: We examined the response of bacteria and proto- and metazooplankton to photomodified dissolved organic matter (DOM). Sterile filtered water from a eutrophic and a humic lake, that was either exposed to artificial ultraviolet (UV) radiation or kept dark, was added to semicontinuous laboratory microcosms that lasted for 7 weeks. Bacterial production responded positively to photochemical modification of DOM regardless of lake type. Final heterotrophic biomass (bacteria1proto1metazooplankton) was 47 ± 5 and 37 ± 5 µg carbon (C) L-1 in microcosms with UVexposed and unaltered eutrophic water DOM and 15 ± 4 and 11 ± 2 µg C L-1 in microcosms with UV-exposed and unaltered humic water DOM, respectively. For the eutrophic water, there were no significant differences in proto- or metazooplankton biomasses between microcosms receiving UV-exposed or nonexposed DOM. Differences between eutrophic water microcosms were not significant when flagellates, ciliates, cladocerans, and copepods were examined separately. In microcosms with UV-exposed humic water, biomasses of heterotrophic flagellates, rotifers, nauplii, and cladocerans were higher than in those with nonexposed DOM. Higher final metazooplankton biomass following addition of UV-exposed humic water indicates that photochemically modified DOM can be effectively transferred through the microbial loop.

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