Uncoupling the microbial loop: growth and grazing loss rates of bacteria and heterotrophic nanoflagellates in the North Atlantic

Abstract

Experiments were conducted in two different oligotrophic areas at 18°N, 30°W and at 33°N, 20°W. Numbers of bacteria and protozoa, namely heterotrophic nanoflagellates (HNF), heterotrophic dinoflagellates and ciliates, were low in both areas, and the average abundance of microorganisms in the euphotic zone varied little. The microbial loop was uncoupled experimentally by differential filtration. Maximum potential growth rates were 0.087 h-1 for bateria and 0.123 h-1 for HNF. Ingestion rates ranged from 9 to 36 bacteria HNF-1 h-1, clearance rates ranged from 0.3 to 3.0 × 10-5 ml HNF-1 h-1. Results confirmed the hypothesis of a linear food chain consisting of bacteria - HNF - larger protozoa which is tightly coupled in the natural environment. -from Authors