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DOI: 10.1127/1863-9135/2009/0175-0171 1863-9135/09/0175-0171 $ 2.50 2009 E. Schweizerbartsche Verlagsbuchhandlung, D-70176 Stuttgart

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

Barry R. Taylor1, *, David J. Garbary1, Anthony Miller1and Felix Brlocher2

With 5 figures and 2 tables

Abstract: The water mouldLeptomitus lacteus bloomed in a small stream in northern Nova Scotia, Canada, for atleast four months from December through March when water temperatures were near 0 C and the stream was fre-

quently 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 rif-

fles and fast-flowing water, evidently because of a high oxygen requirement. In mid-winter, the standing crop ofL.

lacteus approached 2.5 kg m2 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 ofL. 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 thatL. lacteus blooms in winter to take advantage

of a rich food source and high [O2] while avoiding competition. Similar blooms ofL. lacteus elsewhere may be

overlooked because winter weather and ice cover discourage investigations.

Key words:Leptomitus lacteus, Saprochaete saccharophila, bloom, respiration, water mould, winter.

Fundamental and Applied Limnology

Archiv fr HydrobiologieVol. 175/2: 171180, July 2009 E. Schweizerbartsche Verlagsbuchhandlung 2009

Introduction

Leptomitus lacteus (Oomycota) is a filamentous water

mould, widely distributed in flowing, fresh waters of

Europe, North America and Africa (e.g., Yerkes 1966,

El-Hissy 1974, Willoughby & Roberts 1991, Rankovic

2005, Reithmller et al. 2006). While it may be spo-

radically associated with decaying vegetation in pris-

tine environments (Willoughby & Roberts 1991), L.

lacteus is a characteristic component of sewage fun-gus, a collective term for a community of fungi, water

moulds, filamentous bacteria (especially Sphaerotilus

natans) and protozoans that typically develop whitish,

ragged masses on substrata in organically polluted wa-

ter (Butcher 1932, Hynes 1971).

Leptomitus lacteus is usually reported as a minor

component of sewage fungus (Curtis & Curds 1971,

Esho & Benson-Evans 1983), but it may dominate

blooms below pulp mills (Hendry et al. 1982) and

may replace S. natans in winter (Vallin 1958, Rieth-

mller et al. 2006). Nuttall (1973) describes massive

growths ofL. lacteus in February through April in

Cornish streams receiving drainage from landfills.

Sewage fungus in an 18-km length of the Danube

River switched from dominance by S. natans in sum-mer to dominance by L. lacteus in winter, with both

organisms abundant in AprilMay and OctoberNo-

vember (Hlzinger 1978). Hynes (1971) suggests that

L. lacteus may be uncompetitive in low dissolved oxy-

gen waters, and therefore thrives in winter, when or-

Authors addresses:

1 Department of Biology, St. Francis Xavier University, Antigonish, NS, B2G 2W5, Canada.2 Department of Biology, Mt. Allison University, Sackville, NB, E4 L 1E3, Canada.

* Corresponding author; e-mail: btaylor@stfx.ca