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

Aquatic Microbial Ecology

Michael C. Murrell¹  Andrew R. Juhl¹ 

关键词: Phytoplankton growth;    Grazing;    Nutrients;    Dilution experiments;    Pensacola Bay;   

DOI  :  10.3354/ame038147

学科分类：生物科学（综合）

来源: Inter-Research

【 摘 要 】

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 (μ₀) and replete(μ_n) nutrient concentrations. The rates were measured on 4 phytoplankton fractions: bulk, >5 µm, <5 µm, and cyanobacteria. Many similarities existed among phytoplankton fractions: grazing rates were positively correlatedwith both μ₀ and μ_n, the relationship between μ₀ and m was nearly 1:1, and μ_n always exceeded m. The 1:1 relationship between μ₀ and m implied that microzooplanktongrazing accounted for essentially all in situ phytoplankton growth, allowing no net accumulation under ambient nutrient concentrations. Despite this strong grazing pressure, μ₀ < μ_n for all phytoplankton fractions,indicating persistent nutrient limitation. Because μ_n always exceeded m, additional nutrient influx to the sound would generate a disparity between microzooplankton-grazing and phytoplankton-growth rates, resulting in increasedbiomass 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 ofsimultaneous ‘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-growthrates 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.

【 授权许可】

Unknown