Clearance rates of <6 μm fluorescently labeled algae (FLA) by estuarine protozoa: potential grazing impact of flagellates and ciliates

Abstract

Three types of FLA, ranging in size from 1.9-4.5 μm, were made from cultures of Nannochloris atomis, Chlorella capsulata and Thalassiosira pseudonana. Both ciliates and flagellates ingested the FLA at rates greater than they ingested similarly sized fluorescent microspheres. Flagellates 5-10 μm in size predominantly ingested the 2 μm FLA, while oval cells 10 to 15 μm in size, likely athecate dinoflagellates, were important consumers of 3.4 and 5.4 μm FLA. Estimates ciliates, mostly choreotrichs 15-60 μm size, ingested all types of FLA, but with lower clearance rates for the 2 μm FLA than for larger sized FLA. Clearance rates determined for flagellates ranged from 0.004-0.83 μl cell-1h-1, and for ciliates from 0.24-8.3 μl cell-1h-1. -from Authors