Vertical distribution patterns of plankton and their relationship to physical factors over the continental shelf off Oregon

摘要

Discrete layers of phytoplankton and zooplankton were observed over the Oregon continental shelf in summer and fall of 2001 and summer 2002 using optical and acoustical technologies and a pump sampling system. Layers of phytoplankton had steep vertical gradients which were associated with gradients in density and local peaks in shear. These layers had high concentrations of chlorophyll and were persistent for hours to days. The optical signature of co-occurring shallow and deep layers indicated that these layers may have different sources and temporal evolution patterns. Layers of zooplankton were often collocated with layers of phytoplankton. Optical indicators of in-situ grazing were not correlated to zooplankton biomass, indicating that collocated layers containing high abundances of phytoplankton and zooplankton may not be areas of maximal grazing. Acoustic backscatter resolved distribution patterns of zooplankton that were not resolved with stratified net systems or direct pump samples. The size and orientation of zooplankton had large affects on acoustic backscatter and the magnitude of acoustic backscatter was not always correlated to zooplankton biomass.