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0 1997, by Ihc Amctican Society of I~mnology and Oceanography, IllC. Copepod grazing in the equatorial Pacific

By Michael R. Roman and Anne L. Gauzens

Abstract

The vertical distribution of copepod (>64 pm) grazing was mcasurcd on the equator at 14O”W during March/ April (19 d) and October 1992 (21 d). El NiAo conditions prevailed during the March/April time series. Hydrographic variables were similar to the climatological mean during the October time series.,We found higher weight-specific copepod filtration rates in October when mixed-layer temperatures were generally 3°C cooler; there were more phytoplankton B2.0 pm and more Calanoid copepods than in March/April. The grazing impact of the copepod community (biomass X weight-specific filtration rate) was similar for the 64-200-pm copcpod fraction during both time series (0.023 and 0.028 d- I for March/April and October) but was higher in October (0.114 d-l) as compared to March/April (0.040 d-l) for>200-pm copepods. Within-cruise variability was highest in October when a tropical instability wave advected colder water with higher nitrate and chlorophyll through the study area. We observed over six-fold increases in copepod biomass, weight-specific filtration rates, and copcpod grazing rates during this advective event. Grazing rates calculated by assuming that copepods capture only>2-pm phytoplankton (0.25 d-’ in March/April; 0.88 d- ’ in October) suggest that copepod grazing could limit the production of>2-pm phytoplankton, primarily diatoms, in October but not during the El NiHo conditions of March/April when there was less copepod biomass as well as a greater dominance of cyclopoid copepods. Estimates of fecal pellet productio

Year: 2013
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