Grazing by rotifers and crustacean zooplankton on nanoplanktonic protists

Abstract

Predation on nanoflagellates by metazoan zooplankton was investigated using a radioactively labeled flagellate, Poterioochromonas malhamensis, as a tracer cell in laboratory incubations of freshly collected plankton assemblages. Experiments conducted in the fall, winter and spring indicated that rotifers dominated the grazing on nanoflagellates by metazoans in the winter (68%) and spring (92%). Rotifer grazing was not determined in the autumn. It is likely that the greater impact of rotifer grazing in the spring was due to the occurrence of abundant filamentous cyanobacteria and gelatinous colonial phytoplankton which selectively depressed feeding rates of crustaceans compared to rotifers. Crustacean predation on nanoflagellates was highest in the autumn when cladocerans (primarily Daphnia spp.) were abundant. Predation by metazoan zooplankton in this lake appeared capable of removing the total standing stock of heterotrophic and phototrophic nanoplankton in < 1 d. Impacts of ciliated protozoa on nanoplankton, calculated from abundances and literature feeding rates, ranged from approximately one-third to four times that of metazoan predation depending on season and method of calculation. The relative importance of the different groups of predators appears to vary seasonally which is expected to alter the transfer of energy, carbon and nutrients from bacteria to higher trophic levels.

Feeding by heterotrophic dinoflagellates on the common marine heterotrophic nanoflagellate Cafeteria sp.

“…guttula, Luciella masanensis, and Pfiesteria piscicida) are able to ingest the tested species of HNF. Before the present study, ciliates, rotifers, copepods, and cladocerans had been reported to ingest HNFs in aquatic ecosystems (Turner et al 1988, Verity 1991, Sanders et al 1994, Jürgens et al 1996. Therefore, this is the first study reporting the feeding by HTDs on HNFs in aquatic ecosystems.…”

Trophic roles of heterotrophic nanoflagellates and ciliates among planktonic organisms in a hypereutrophic pond

“…Since HNF (Nakano 1994) and ciliates (Stoecker & Capuzzo 1990) are rich in nitrogen and phosphorus, as are bacteria (Nagata 1986, Vadstein et al 1988, they can be qualitatively good food for their predators. Previous studies have demonstrated efficient predation on HNF by oligotrichous ciliates (Jurgens et al 1996), high predation pressure on HNF by rotifers (Dolan & Gallegos 1991. Sanders et al 1994) and on ciliates by copepods (Burns & Gilbert 1993, Dobberfuhl et al 1997).…”

“…Although a great abundance of the genus Daphnia sometimes makes the microbial loop less important (Pace & Funke 1991, Nakano et al 1998, HNF (Sanders & Porter 1990, Carrick et al 1991 'E-mad: shin@agr.ehirne-u.ac jp O Inter-Research 1998 1994, Sanders et al 1994) and ciliates (Tezuka 1974, Carrick et al 1991, Sanders et al 1994) are also considered to be important links in the transfer of bacterial biomass to metazoan zooplankton. Since HNF (Nakano 1994) and ciliates (Stoecker & Capuzzo 1990) are rich in nitrogen and phosphorus, as are bacteria (Nagata 1986, Vadstein et al 1988, they can be qualitatively good food for their predators.…”

Cascading trophic effects on aquatic nitrification: experimental evidence and potential implications

“…However, none of the zooplankton species in this study should be considered to be highly efficient bacterial grazers based on construction of their food gathering structures (Vanderploeg 1994). On the other hand, the same or similar zooplankton species prey upon protists (Hartmann et al 1993, Jack & Gilbert 1993, Sanders et al 1994. The grazing control of nanoheterotrophs by planktonic microciliates is also well documented (e.g.…”