Sources of variability in measurements of copepod lipids and gut fluorescence in the California Current coastal zone

Abstract

The spatial association of zooplankton nutritional state with particulate food abundance was tested along the central California coast in March 1986. Suspension-feeding copepods (Metn'da pacifica, Calanus pacificus californicus, Rhincalanus nasutus, Eucalanus cahfornicus) and suspended particulate matter were sampled at stations with median nearest neighbor distance of 19.6 km. In this field condition of relatively small horizontal gradients in food supply, copepod gut fluorescence, triacylglycerols and wax esters showed little or no association with spatial variations in particulate nitrogen, particulate carbon or chlorophyll a. In contrast, strong diel variation in gut fluorescence was observed including post-sunset increases in ingestion. For the conditions observed during this study, diel variations in feeding behavior explained more of the variance in copepod ingestion than did horizontal variations in food supply. Efficiency of extraction of copepod lipids by homogenization and by standng in chloroform: methanol was also compared. A new double development, single scan method for separation and analysis of zooplankton lipids by Thin Layer Chromatography/Flame Ionization Detection is presented.