A comparative study on the carotenoid pigmentation of the zooplankton of Lake Maarsseveen (Netherlands) and of Lac Pavin (Auvergne, France)—II. Diurnal variations in carotenoid content

Abstract

1. 1. Diurnal studies have been executed on carotenoid content of zooplankton of the sandpit Lake Maarsseveen and of the mountain lake, Lac Pavin. 2. 2. With the vividly red-pigmented zooplankton of Lac Pavin conclusive evidence was found for a distinct 2.5-fold day/night rhythm in the content of carotenoid pigments, showing minima around midday and maxima around midnight. A comparable, less pronounced 1.7-fold diurnal change was detected for the content of keto-carotenoid pigments of the zooplankton of Lake Maarsseveen. 3. 3. In addition to the previously reported differences in quantitative and qualitative aspects of carotenoid pigmentation of the zooplankton of the two lakes, the amplitude of diurnal changes in carotenoid content would also indicate a more elaborate carotenoid metabolism with the zooplankton of Lac Pavin. 4. 4. Explanations as to the complexity of the more or less irregular diurnal patterns are discussed. It is suggested that diurnal changes in carotenoid content, whether or not interacting with diurnal rhythms in accumulation and consumption of lipid reserves, are a manifestation of some circadian physiological periodicity in planktonic crustaceans, and are closely associated with diurnal vertical migration and feeding periodicity.