Abstract:
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.
