Trophic linkage among heterotrophic nanoflagellates, ciliates and metazoanzooplankton in a hypereutrophic pond

We examined seasonal abundance, production and loss to predation of heterot rophic nanoflagellates (HNF) and ciliates in order to clarify food linkages among HNF, ciliates and metazoan zooplankton in a hypereutrophic pond. Pro duction and loss rates of the protists were estimated using size fractionat ion (< 5 mum, < 30 mum and total) experiments. There were coupled oscillati ons in seasonal abundance between HNF and ciliates, whereas we found none b etween the protists and metazoan zooplankton. Seasonal trends in production of HNF (-12.4 to 86.4 ng C ml(-1) d(-1)) and predation rates on them by ci liates (-25.6 to 52.2 ng C ml-1 d-1) were similar. There were significant c orrelations (p < 0.05) between HNF production and predation on HNF by cilia tes. These results indicate that ciliates are major consumers of HNF, but w e have insufficient evidence of predation on HNF by metazoan predators to d o more than suggest that food linkage between HNF and metazoan predators is not substantial. The dominant ciliate species were Cinetochilum margaritac eum, Urothcha spp., Halteria grandinella and Cyclidium glaucoma. Growth rat es of Urotricha and Cyclidium populations were enhanced by removal of metaz oan predators when the ciliates were dominant. We detected substantial pred ation pressure on Urotricha spp. during its period of dominance and found a significant correlation (p < 0.02) between production and predation of C. glaucoma. Thus, we suggest that there are active food linkages between thes e 2 ciliates and metazoan predators. For C. margaritaceum and H. grandinell a, we did not have enough evidence to suggest predation by metazoan predato rs. Thus, we showed over a 1 yr period that HNF production was almost balan ced by loss to predation by ciliates, and that loss processes other than pr edation might be important for some ciliate taxa.