Seasonal dynamics of phytoplankton and zooplankton biomass off Monterey Bay, California

Amy Little
U.S. Geological Survey

Wednesday, October 1, 2003
Pacific Forum 3:00 p.m.

During 19982000, the seasonal cycles of phytoplankton and zooplankton were examined from moorings deployed in central California waters using the biological variables of fluorescence and acoustic backscatter and the physical variables of temperature and velocity. Annual composites for each of the biological and physical variables were constructed from the data series in order to extract the cross-shore seasonal pattern and to examine relationships among these variables. A cross-shore chlorophyll gradient, with peak average chlorophyll values of 3.3 μg/l, was discovered at the most inshore site of the Monterey submarine canyon. For zooplankton the peak biomass of 726 mg/m2 was measured at the mid-shore site. Cross-site analysis of depth-integrated zooplankton biomass, measured by acoustic backscatter, indicates that offshore zooplankton populations peak earlier than inshore zooplankton populations. Furthermore, time lag analysis suggests that higher inshore chlorophyll biomass is followed by higher mid-shore zooplankton biomass. With offshore zooplankton populations leading the zooplankton productivity, it is hypothesized that offshore zooplankton populations migrate onshore during periods of high primary production.  

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