Growth and physiology of nuisance alga Hincksia sordida during a bloom in South East Queensland, Australia

Nuisance blooms of macroalgae are increasingly common in response to nutrient pollution of the coastal zone. In Queensland Hincksia sordida, a filamentous brown alga, have been increasing in the Noosa area in summer over the last two decades. Because the Noosa area is relatively unpolluted compared to other locations where blooms are common our study was aimed at determining the sensitivity of the algae to nutrient availability and characterizing the physiological state of the algae throughout the bloom period. Although physiological condition of the algae fluctuated over the summer, algae were observed to have high rates of photosynthetic electron transport in the field and had high growth rates when cultured in the laboratory. Nitrogen (N) to Phosphorus (P) ratios of the algal tissue indicated that growth was N limited for most of the summer bloom period. Laboratory tests of the response of algal growth to nutrient availability found Hincksia sordida to be highly sensitive to N availability, achieving maximum growth rates at ammonium concentrations of 2–3 μM. We conclude that due to the alga's high sensitivity at low N concentrations blooms of Hincksia sordida may be sustained at low levels of nutrient availability.