Response of lower trophic organisms to nutrient input and effects on carbon budget: a mesocosm experiment

Response of lower trophic organisms to nutrient input and effects on carbon budget: a mesocosm experiment
Publication Type
Journal Article
Year of Publication

Tsuda A, Fukami K, Kiyosawa H, Suzuki K, Takeda S, Nishioka J, Takahashi M, Johnson K, Wong CS

Plankton & Benthos Research
ISBN Number

Bacteria, copepods, diatom bloom, heterotrophic dinoflagellate, mesocosm, microzooplankton, trophodynamics, Patricia Bay, British Columbia, Canada, 20 m3


Abstract: The roles of heterotrophic organisms (microzooplankton, mesozooplankton, bacteria and heterotrophic nanoflagellates) were examined during a nutrient enrichment experiment using a mesocosm in Saanich Inlet, British Columbia, Canada. Grazing rates of microzooplankton, copepods, and Noctiluca scintillans were respectively estimated by the dilution method, from the egg production, and the apparent growth rate. The primary production increased by about 11 times during the initial 3 days, and the grazing rate by zooplankton also increased by 7.4 times. The primary production exceeded the grazing rate during the initial 5 days, after that, almost balanced rates were observed. Biomass peaks of bacteria and HNFs (heterotrophic nanoflagellates) were observed after the decline of the phytoplankton bloom. Bacterial production and HNF bacterivory gradually increased from the beginning to the end of the experiment. Microzooplankton consistently removed about half of the primary production. The contribution of microzooplankton to grazing was largest during the initial 7 days. Heterotrophic dinoflagellates were the most dominant component of the microzooplankton, but oligotrich ciliates showed the fastest growth response to phytoplankton production. Noctiluca scintillans became an important grazer after the bloom. Overall, the contribution of microzooplankton grazing was the largest of the processes through which phytoplankton were lost. Cell sinking was a minor component contributing to loss of phytoplankton. Thus, oligotrich ciliates and heterotrophic dinoflagellates were the most plausible organisms contributingto the steady state of phytoplankton concentrations.

Date of Published
Accession Number
Type of Article
Alternate Journal