Diatom fouling problems in a Tasmanian Hydro Canal, including the description of Gomphonema tarraleahae sp. nov

Open air freshwater hydrocanals in Tarraleah, Tasmania, Australia, exhibit significant diatom biofouling which leads to economic losses in hydroelectricity generation. These fast-flowing (flow velocity 2 m s-1) canals produce between 2 and 18 tonnes dry weight of fouling and 1-5 mg chlorophyll a/m2 over a 20 km long course, with the canal surface area being 192,000 m2. Mostly monospecific diatom communities of Tabellaria flocculosa occur in canal sections with reduced flow, whereas a stalk-forming (up to 200 μm long) Gomphonema species dominates the majority of canal fouling in fast flowing areas. Gomphonema tarraleahae Perkins et Hallegraeff is newly described, the species differing from its close relative, G. angustatum (Kützing) Rabenhorst in its extreme stalking habit and distinctive head and footpoles. Low numbers of G. subclavatum (Grunow) Grunow and two other undescribed Gomphonema species were also present in fouling. Seasonal changes in biofouling are most likely related to temperature (5-15°C annually) and light intensity variation, with shaded, south-facing walls exhibiting higher fouling densities. Implications for fouling mitigation strategies are discussed.