Nuisance mucilage produced by Lindavia intermedia (Bacillariophyceae) in New Zealand lakes

The invasive centric diatom Lindavia intermedia arrived in New Zealand in recent decades. It produces a pelagic mucilage, which forms an adhesive substance known as lake snow. While determining cell concentrations of L. intermedia is relatively straightforward, methods to estimate mucilage concentration in lake water have not yet been developed. Two methods for lake snow quantification are reported here: a dragged line, or "snow tow," and in situ filtration. A chemical assay for hexosamine, as an estimate of chitin content, and an atomic absorption method, which measures silicon, were used to measure these components of lake snow. Samples from 4 lakes revealed a correlation between snow tow and filtration data; in principle, the snow tow method (used by municipal authorities) could be calibrated and made quantifiable using the filtration method. Expression of the chitin synthase gene in summer/autumn (but not in winter/spring) correlated with abundance of the chitin component of lake snow, aligning with anecdotal evidence for the timing of its development in lakes. By contrast, cell densities correlated poorly with lake snow abundance. Cell concentrations relative to chitin concentrations were also higher in winter/spring than in summer/autumn across lakes. Dry weight and silicate in lake snow relative to chitin varied by lake and season. The quantification of lake snow and its adhesiveness are important parameters for assessing its nuisance value and fouling characteristics and for developing measures to prevent and remediate its incursion in lakes.