Long term seagrass monitoring in Cairns Harbour and Trinity Inlet: December 2006

This report details results from the December 2006 seagrass monitoring survey for Cairns Harbour and Trinity Inlet conducted as part of an annual long term monitoring program. The monitoring program was established following a baseline survey in December 2001 and examines selected representative seagrass meadows in Cairns Harbour and Trinity Inlet. Total area of each monitoring meadow, species composition and seagrass density (above ground biomass) were measured for comparison with previous surveys. In 2006 seagrasses in Cairns were generally healthy with total area of seagrass meadows the highest since monitoring began in 2001 and biomass for the largest meadows remaining relatively high. Within the overall area and biomass trends there were differences between intertidal and subtidal meadows and between meadows in Cairns Harbour and Trinity Inlet. There was also a substantial change to seagrasses to the south of Bessie Point resulting in the establishment of a new meadow. The changes to Cairns Harbour and Trinity Inlet seagrass meadows appear to be strongly linked to local and regional climate conditions and generally reflected similar changes that have occurred to seagrasses in other areas of Queensland over the same time period. The increases in intertidal seagrasses in the harbour and declines in deeper subtidal meadows further up the inlet were consistent with a return to more "normal" rainfall, temperature and light conditions over the past three years. The increased abundance of seagrass in Cairns Harbour may have flow on effects for fisheries in the area especially tiger and endeavour prawns which utilise these areas as a nursery ground. There was also an increase in seagrass species that are preferred as a food source by dugong and green turtles. Results of monitoring in 2006, combined with similar monitoring in other north Queensland locations, indicate that seagrass habitats and the marine environment in Cairns Harbour and Trinity Inlet were relatively healthy. The monitoring program has developed our understanding of the relationships between climatic changes, anthropogenic disturbance and seagrass abundance and has shown that there have been minimal impacts associated with current port and urban activities