Contribution of rotifers to the diet and fitness of Boeckella (Copepoda: Calanoida)

1. The calanoid copepods, Boeckella triarticulata Sars and Boeckella hamata Brehm, are major components of the freshwater zooplankton of New Zealand. It was not known whether these copepods ingest rotifers, nor whether the inclusion of rotifers in their diets might improve their fitness. The present study aimed to identify rotifer taxa which are eaten by each copepod species, and to examine the fitness consequences of the inclusion of one species of rotifer in the diet of B. triarticulata .
2. In feeding experiments using natural rotifer assemblages, both species of copepod ingested the rotifer Anuraeopsis fissa (0.4–4% of daily carbon intake), and B. triarticulata also ingested Polyarthra dolichoptera (6–30% of daily carbon intake) and Keratella cochlearis tecta (1% of daily carbon intake).
3. The contribution of rotifers to the fitness of adult female B. triarticulata was assessed by comparing survival and reproduction among five diets that contained varying densities of algae ( Cryptomonas sp.) and/or Polyarthra dolichoptera (4 μg C L⁻¹). Boeckella triarticulata produced fewer clutches on a rotifer-only diet than on a solely algal diet, and addition of rotifers to a threshold algal diet did not affect copepod fitness relative to the solely algal diets. The present results suggest that Polyarthra at 4 μg C L⁻¹ is not a high-quality food for B. triarticulata .