Long term seagrass monitoring in Cairns Harbour and Trinity Inlet: December 2008

This report details results from the October/December 2008 seagrass monitoring survey for Cairns Harbour and Trinity Inlet and discusses changes in inter-annual seagrass meadow dynamics. Following a baseline survey of Cairns Harbour and Trinity Inlet, a monitoring program was established in December 2001 that annually examines selected representative seagrass meadows in the area. Results of the program are used to ensure port and other human activities are having a minimal impact on the marine environment by using seagrasses as a key indicator of marine environmental health. The program is also used to assess the status of these important fisheries habitats and forms part of a network of seagrass assessment established throughout Queensland.\ud \ud Results of the 2008 monitoring survey indicate that seagrass habitat in Cairns Harbour and Trinity Inlet was in a fair condition. The density of intertidal monitoring meadows had either increased significantly or remained relatively stable compared to the previous year of monitoring, a positive change from three consecutive years of biomass decline. Meadow area remained at similar levels to the previous year for the intertidal meadows. The opposite was true for the small subtidal monitoring meadows within Trinity Inlet where some significant declines in both biomass and area were recorded. Density and distribution of these small Inlet meadows has been highly variable over the past few years and they are particularly vulnerable to additional stresses in the future.\ud \ud The observed changes in biomass and distribution of the Cairns monitoring meadows have been linked to regional and local climate conditions. However the current lack of marine environmental data at the meadow level makes interpretation of the observed changes in Cairns Harbour and Trinity Inlet seagrass difficult. Several enhancements to the monitoring program are suggested that would strengthen the ability to separate out the causes of seagrass change and better inform the management and protection of seagrasses in the future. These include:\ud \ud • Assessing light and temperature at the meadow level (in situ loggers)\ud \ud • Examining reproductive and recovery capacity of the meadows\ud \ud • Expanding the geographic scope of the area examined to a broader region and incorporating additional monitoring meadows\ud \ud • Linking water quality assessment with seagrass condition\ud \ud The seagrass meadows of Cairns Harbour and Trinity Inlet have been identified as one of four regions in the Great Barrier Reef World Heritage Area (GBRWHA) facing the highest level of risk from anthropogenic impacts. Continued impacts from natural events have the capacity to reduce the resilience of seagrasses in the region due to compounding effects of current human activities such as urbanisation and coastal and port development. The vulnerable state of some seagrasses in Trinity Inlet underscores the value of continued monitoring to ensure the long term viability of these marine habitats