Macroalgae in Lake Illawarra, New South Wales, Australia

Abstract

Macroalgal blooms are a recurring problem in Lake Illawarra, and other shallow urbanized estuaries throughout the world. Since 1988, macroalgal harvesting has been used as a management tool in Lake Illawarra, although the ecological impacts of this harvesting are not yet known. Ecologically sustainable management of macroalgae requires knowledge of the environmental factors determining macroalgal abundance and diversity, and the key factors limiting the growth of those species. This paper reports on some of the main issues relating to the excessive growth of macroalgae in Lake Illawarra. The biomass, distribution, species composition and nutrient contents of macroalgae in Lake Illawarra were examined between 2000 and 2003. At least 35 species (16 green, 10 red and 9 brown) of macroalgae currently exist in the Lake, with the most problematic species being the opportunistic chlorophyte Chaetomorpha linum. Macroalgae generally had high tissue nitrogen concentrations (up to 3.87 % dry wt.), reflecting the high nitrogen storage capacity, despite Lake Illawarra being considered nitrogen limited. Macroalgal biomass has dropped considerably since the mid-1990s, although nuisance algal blooms still occur periodically, particularly following wet weather.