Does the red tide-forming dinoflagellate Noctiluca scintillans feed on bacteria?

Investigations were made to determine if Noctiluca scintillans is able to remove and ingest bacteria and thus influence bacterial numbers in the water column, before and after a Noctiluca 'bloom' (red tide). Laboratory experiments were performed with bacteria-sized fluorescent latex microspheres of 0.5, 1.1, and 4.5 mu m diameter, as well as with live cells of the bacteria Vibrio sp. and Serratia plymuthica. Results indicate that Noctiluca can remove microspheres and bacteria at a rate of 10(4) to 10(6) individual(-1) hour(-1), under the given laboratory conditions. Data on abundance of Noctiluca, different groups of bacteria, yeasts, nanoflagellates, and microbial exoenzyme activity in the southern North Sea are compared. Although removal of bacteria by Noctiluca in the field is generally not reflected in the occurrence of these organisms, it is possible that Noctiluca ingests bacteria in the winter when other food sources are scarce. During its exponential growth, Noctiluca may remove bacteria from the water column together with other potential and actual food organisms trapped in its mucoid webs.