Diel fluctuation in zooplankton grazing rate as determined from the downward vertical flux of pheopigments
نویسندگان
چکیده
The diel grazing activity of zooplankton was measured at a single study site in a temperate fjord, Dabob Bay, Washington, USA at several periods during spring, summer and fall of 1979-1981. Pheopigments were used as an indicator of herbivorous zooplankton activity. The downward vertical flux of pheopigment-containing fecal pellets was measured with sediment traps deployed over repetitive 4 h periods. Experiments were run for 24 to 36 h. A maximum in the flux of pheopigments was consistently noted within the euphotic zone during hours of darkness. Diel fluctuations in pheopigment flux showed amplitudes up to 29-fold. Nightly grazing activity accounted for 41 to 82% of the daily (24 h) grazing and was indirectly related to seasonal changes in daylength.
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