Protozoans in two southeastern blackwater rivers and their importance to trophic transfer

Abstract

Protozoan population densities in the sixth-order Ogeechee River and fourth-order Black Creek ranged from 6 x lo4 to 11 x 10" flagellates liter-l and 0 to 1.5 x lo5 ciliates liter-' over a 12-month period. These numbers approximate those reported for various marine and freshwater habitats. A microcosm study with Ogeechee River water showed a density increase from 4 x lo5 to 9 x lo6 flagellates liter -I and 7 x 10) to 4 x lo5 ciliates liter-' in 2 d, representing an estimated net protozoan production of 600 pg C liter -I d-l. This production was mainly attributed to bacterial growth on DOC and subsequent grazing by the protozoans. Although problems always accompany container studies, this indicates an immense potential for protozoan production in the river. Daily transport of protozoan carbon ranged from 1.08 to 1,360 g, and annual estimated transport downstream was 60 t of protozoan carbon in the Ogeechee River. Densities of filter-feeding macroinvertebrates are very high in this river. Many of the filter-feeding species are known to feed primarily on amorphous material in the seston, within which protozoans consitute about 4% by carbon content. Since protozoans can be assimilated at relatively high efficiency (-50%), they appear to bc a trophic link between the metazoans and otherwise unavailable carbon sources in blackwater rivers.

Remineralization of organic matter and degradation of the organic fraction of suspended solids in the River Danube

“…The predominance of small bacteria (0.24 pm3; Kasimir 1992) and a high flagellate abundance (mean: 4.6 X 103 ml-') in the River Danube support this conclusion. The flagellate abundance found in this study is in good agreement with that reported by Kasimir (1992) (range: 1 to 22 X 103 ml-l); similarly, Carlough & Meyer (1989) found l l X 103 flagellates ml-' in the Ogeechee River. Despite high flagellate numbers commonly occurring in rivers, Fenchel (1986) noted that protists are not important in lotic systems because of high wash-out rates.…”

“…Despite high flagellate numbers commonly occurring in rivers, Fenchel (1986) noted that protists are not important in lotic systems because of high wash-out rates. Calculating the community grazing rate for the River Danube according to Carlough & Meyer (1989) and assuming a clearance rate of 10-M l flagellate-' h-' (Andersson & Fenchel 1985), 44.4 X 10"ells ml-' d-' are grazed. Converting this grazing rate into carbon equivalents (assuming a carbon content of 20 fg cell-'; Lee & Fuhrman 1987), 88.8 pg C 1-' d-' are consumed, which is close to the mean bacterial production of 71 pg C I-' d-' in the River Danube.…”

Développement du phytoplancton, des Ciliés et des Rotifères sur deux sites de la Loire moyenne (France), en période d'étiage

“…Un minimum de 200 cellules est compté pour chaque échantillon fixé. Un biovolume moyen est estimé en mesurant une cinquantaine de cellules à l'aide d'un micromètre oculaire et en assimilant ces cellules à des sphères (Carlough & Meyer 1989) ; dans le cas de formes ovoïdes, nous avons considéré une dimension moyenne. Différents ouvrages de détermination ont été consultés (Ward & Whipple 1966, Jahn et al 1979, De Puytorac et al 1987, Finlay et al 1988, Foissner & Berger 1996.…”

The importance of Daphnia in determining mortality rates of protozoans and rotifers in lakes

“…The abundance and biomass of planktonic protozoa tend to be correlated with the availability of resources within and among systems (e.g. Pace 1982;Carlough and Meyer 1989;Sanders et al 1992), but there is also evidence that larger zooplankton may limit the abundance and biomass of protozoa in lakes. For example, the ratio of bacteria to heterotrophic flagellates is -1,000 : 1 across trophic gradients in marine and freshwater systems (Sanders et al 1992).…”