The role of benthic microalgae in the ecology of Lake Illawarra

Benthic microalgae (BMA) are an important component of shallow coastal ecosystems, as they contribute significantly to primary production, nutrient cycling and sediment stabilisation. Despite the importance of these processes to the health of estuaries and especially coastal lagoons, there are few studies of BMA in Australian estuaries. This study examined the spatial and seasonal variation in the biomass and distribution of BMA in Lake Illawarra, on the south coast of NSW. Sediment cores were collected throughout the lake on 6 occasions between October 1999 and August 2001. The upper 5mm of these sediment samples were analysed for chlorophyll a. Water quality and light attenuation were also measured. Biomass of BMA varied from 4.2 – 74.3 mg/m2 and was generally higher in shallow sandy areas compared to the deep mud basin. High turbidity is likely to restrict benthic productivity primarily to the shallow areas where light can penetrate to the benthos. However, due to low light adaptation by BMA, increases in water clarity are likely to increase BMA activity and function significantly throughout the lake. This study has highlighted the profound differences in the biological activity of shallow sandy areas vs deep muddy areas within the lake.