Original paper

Metabolism and ecology of the water mould, Leptomitus lacteus (Oomycota), blooming in winter in a Nova Scotia stream

Taylor, Barry R.; Garbary, David J.; Miller, Anthony Bärlocher


The water mould Leptomitus lacteus bloomed in a small stream in northern Nova Scotia, Canada, for at least four months from December through March when water temperatures were near 0 °C and the stream was frequently ice-covered. The bloom occupied much of the substratum along 1.5 km of stream below the effluent outfall from a composting facility. A true fungus, Saprochaete saccharophila, was a minor component of the bloom. L. lacteus colonies appeared robust against freezing and regrew quickly after scouring floods. L. lacteus preferred riffles and fast-flowing water, evidently because of a high oxygen requirement. In mid-winter, the standing crop of L. lacteus approached 2.5 kg m−2 fresh mass, or 2000 kg along the whole length of stream. The bloom ended abruptly in April when water temperatures rose above 5 °C. In the laboratory, clumps of L. lacteus demonstrated vigorous oxygen consumption near 0 °C. Oxidative metabolism was largely confined to the outer 6 mm of the colonies, interior to which [O2] declined precipitously. Evidence suggests that L. lacteus blooms in winter to take advantage of a rich food source and high [O2] while avoiding competition. Similar blooms of L. lacteus elsewhere may be overlooked because winter weather and ice cover discourage investigations.


leptomitus lacteussaprochaete saccharophilabloomrespirationwater mouldwinter