Interactions between nutrients, phytoplankton growth, and microzooplankton grazing in a Gulf of Mexico estuary

Publication Status is "Submitted" Or "In Press: 
LDEO Publication: 
Publication Type: 
Year of Publication: 
2005
Editor: 
Journal Title: 
Aquatic Microbial Ecology
Journal Date: 
Feb 9
Place Published: 
Tertiary Title: 
Volume: 
38
Issue: 
2
Pages: 
147-156
Section / Start page: 
Publisher: 
ISBN Number: 
0948-3055
ISSN Number: 
Edition: 
Short Title: 
Accession Number: 
ISI:000227276200005
LDEO Publication Number: 
Call Number: 
Abstract: 

Dilution grazing experiments were conducted on 9 dates over a 16 mo period in Santa Rosa Sound (Florida, USA) measuring microzooplankton grazing (m) and phytoplankton gross-growth rates under in situ (mu(0)) and replete (mu(n)) nutrient concentrations. The rates were measured on 4 phytoplankton fractions: bulk, >5 pm, <5 pm, and cyanobacteria. Many similarities existed among phytoplankton fractions: grazing rates were positively correlated with both mu(0) and mu(n), the relationship between mu(0) and m was nearly 1: 1, and mu(n) always exceeded m. The 1: 1 relationship between mu(0) and m implied that microzooplankton grazing accounted for essentially all in situ phytoplankton growth, allowing no net accumulation under ambient nutrient concentrations. Despite this strong grazing pressure, mu(0) < mu(n) for all phytoplankton fractions, indicating persistent nutrient limitation. Because mu(n) always exceeded m, additional nutrient influx to the sound would generate a disparity between microzooplankton-grazing and phytoplankton-growth rates, resulting in increased biomass in all phytoplankton fractions. However, grazing would remain a major loss term for phytoplankton such that quantitative prediction of the biomass increase would have to incorporate grazing rates. This study therefore provides a useful example of simultaneous 'top-down' and 'bottom-up' control of phytoplankton biomass, We additionally observed that increased nutrient availability led to greater dominance by larger eukaryotic phytoplankton, due to differences in gross-growth rates between the phytoplankton fractions rather than differential grazing. Grazing rates on and gross-growth rates of cyanobacteria, but not the other phytoplankton fractions, were strongly correlated to temperature.

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901IMTimes Cited:8Cited References Count:44

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