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 in clusion of rotifers in their diets might improve their fitness. The present study aimed to identify rotifer taxa which are eaten by each copepod speci es, and to examine the fitness consequences of the inclusion of one species of rotifer in the diet of B. triarticulata. 2. Ln feeding experiments using natural rotifer assemblages, both species o f copepod ingested the rotifer Anuraeopsis fissa (0.4-4% of daily carbon in take), and B. triarticulata also ingested Polyarthra dolichoptera (6-30% of daily carbon intake) and Keratella cochlearis tecta (1% of daily carbon in take). 3. The contribution of rotifers to the fitness of adult female B. triarticu lata was assessed by comparing survival and reproduction among five diets t hat contained varying densities of algae (Cryptomonas sp.) and/or Polyarthr a dolichoptera (4 mu g C L-1). Boeckella triarticulata produced fewer clutc hes on a rotifer-only diet than on a solely algal diet, and addition of rot ifers to a threshold algal diet did not affect copepod fitness relative to the solely algal diets. The present results suggest that Polyarthra at 4 mu g C L-1 is not a high-quality food for B. triarticulata.