Water and organic content of boreal macrozooplankton and their significance for the energy content

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Abstract
Interspecific and intraspecific variation in the proportion of water and organic matter are presented for 18 species of macrozooplankton from Kosterfjorden, western Sweden, sampled over a period of one year. Crustacean species have a water content of between 70 and 84 % of the wet weight and an organic content of between 80 and 95 % of the dry weight. Gelatinous species have a water content of more than 90 % of the wet weight and an organic content of 19 to 82 % of the dry weight. The proportion of water tends to decrease and the proportion of organic matter tends to increase with increasing size of the individual in most species. The proportion of water and organic matter show opposite seasonal trends, with high values for the former from winter to early spring and low values from summer to autum. High energy content in relation to organic content indicates that boreal macrozooplankton represents a group of species that store energy as a strategy to survive unfavourable periods in their life cycles. Equations are given for the relationships between water proportion and organic proportion, water proportion and weight-specific energy content, and organic proportion and weight-specific energy content.