Macroalgae, in the Upper Yarra and Watts River catchments: Distribution and Phenology

Abstract

Studies on the floristics and phenology of macroalgal communities in the upper Yarra and Watts River catchments have shown that the urbanized reaches of the Yarra River near Warburton are relatively species-rich and that they include nearly all macroalgal taxa found in protected catchments upstream. The lower of three river sites near Warburton, however, includes fewer species and is seasonally dominated by Vaucheria bursata, a saproxenous alga. The macroalgal communities on solid rock are distinct from those on loose rock subject to flood movement, and they include more taxa with basally attached filaments. A nearby enriched tributary, McMahons Creek, is dominated by a Spirogyroideae species and is species-poor. Species richness is also low on small-weirs and natural stream habitats in protected upstream catchments. Experimental timber harvesting above a series of small-weirs introduced weed species into the streams, replacing some of the native macroalgal species. Indigenous macroalgal species return 5 or so years after selective timber thinning, but they do not return even 10 years after clear-felling and fertilizing. The macroalgae of the upper Yarra River basin can be grouped into those that can grow throughout the year, those whose growth is restricted by water temperature, and those with a distinct seasonality unrelated to water temperature.