Effects of Zooplankton Grazing on Phytoplankton Size-Structure and Biomass in the Lower Hudson River Estuary

The impact of mesozooplankton (>210 μm, mostly adult copepods and late-stage copepodites) and micrometazoa (64-210 μm, mostly copepod nauplii) on phytoplankton size structure and biomass in the lower Hudson River estuary was investigated using various 14 C-labeled algal species as tracers of graz...

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Bibliographic Details
Published in:Estuaries 1996-12, Vol.19 (4), p.874-889
Main Authors: Lonsdale, Darcy J., Cosper, Elizabeth M., Doall, Michael
Format: Article
Language:English
Subjects:
Animal and plant ecology
Animal, plant and microbial ecology
Biological and medical sciences
Brackish
Brackish water ecosystems
Carbon
Copepoda
Diatoms
Ditylum brightwellii
Egg production
Estuaries
Fundamental and applied biological sciences. Psychology
Ingestion
Phytoplankton
Plankton
Primary productivity
Surface water
Synecology
Thalassiosira pseudonana
Zooplankton
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Summary:The impact of mesozooplankton (>210 μm, mostly adult copepods and late-stage copepodites) and micrometazoa (64-210 μm, mostly copepod nauplii) on phytoplankton size structure and biomass in the lower Hudson River estuary was investigated using various 14 C-labeled algal species as tracers of grazing on natural phytoplankton. During spring and summer, zooplankton grazing pressure, defined as% = mg C ingested m-2 h-1 mg C produced m-2 h-1 (depth-integrated rates) × 100, on total phytoplankton ranged between 0.04% and 1.9% for mesozooplankton and 0.1% and 6.6% for micrometazoa. The greatest grazing impact was measured in fall when 20.2% and 44.6%, respectively, of the total depth-integrated primary production from surface water phytoplankton was grazed. Mesozooplankton exhibited some size-selective grazing on phytoplankton, preferentially grazing the diatom Thalassiosira pseudonana over the larger diatom Ditylum brightwelli, but this was not found for micrometazoa. Neither zooplankton group grazed on the dinoflagellate Amphidinium sp. We conclude that metazoan zooplankton have a minimal role in controlling total phytoplankton biomass in the lower Hudson River estuary. Differences in the growth coefficients of various phytoplankton size-fractions-not grazing selectivity-may be the predominant factor explaining community size-structure.
ISSN:0160-8347
1559-2758
DOI:10.2307/1352304