Some characteristics of the carbon compounds released by Daphnia

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Abstract
The Daphnia species studied released 18–100% of the algal carbon ingested as dissolved and particulate carbon compounds, presumably mainly as feces. The particulate fraction constituted on average 79 ± 5% of the total released compounds, leaving 21% as dissolved compounds. The particles released were very small and transparent, not visible by light microscopy Moreover, they contained significant amounts of chlorophyll derivatives. The dissolved compounds consisted mainly of small molecules (mol. wt >103 daltons), and were shown to be utilized by planktonic bacteria. Our results show that particulate organic carbon and chlorophyll a should not be used as measures for algal carbon in grazing experiments with Daphnia. Both these parameters were influenced by the animals' fecal particles, yielding lowered clearance rates compared with those obtained by using cell numbers as a measure for algal carbon.

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