The presence of chlorophyll b and the estimation of phaeopigments in marine phytoplankton

A reverse-phase h.p.l.c. technique was used to estimate the concentration of chlorophyll b in phytoplankton cultures, fecal pellets of Calanuipacificus, and suspended paniculate matter from the Central North Pacific, Oregon coastal waters, and Dabob Bay (a temperate fjord in Puget Sound, WA, USA). The purpose was to assess the distribution of this pigment in the euphotic zone and its effect on the fluorometnc estimation of phaeopigments. Analyses of natural waters confirm high chlorophyll b concentrations (median mass ratio of Mb:a > 0.3) at the depth of the chlorophyll a maximum in tropical waters while values for temperate plankton are relatively low (median mass ratio of chl b:a = 0.05) and patchy. Zooplankton fecal pellets showed a significant enrichment in chlorophyll b, suggesting grazing as a mechanism to explain high concentrations of this pigment at the bottom of the euphotic zone. It is estimated that the presence of chlorophyll b could cause an average overestimation of phaeopigment concentration by the fluorometric technique of 38% between 0 and 200 m in the Central North Pacific. This effect is more pronounced at the layer of chlorophyll b maximum (120-140 m).