Long-term seagrass monitoring in Port Curtis and Rodds Bay, Gladstone: October/November 2004

This report details findings of the first of planned annual seagrass monitoring surveys for Port Curtis and Rodds Bay conducted in November 2004. The program was developed from a baseline survey conducted in 2002 and from recommendations of the Port Curtis Integrated Monitoring Program (PCIMP) review. This survey found that there were some significant changes to the seagrass monitoring meadows between 2002 and 2004. The factors driving seagrass changes had different effects on intertidal and subtidal seagrass meadows, with negative changes occurring in most intertidal meadows but increases in area and density occurring for subtidal meadows. Accompanying the reduced density of intertidal seagrass was a shift in species dominance with "pioneering" Halophila ovalis displacing Zostera capricorni as the dominant species for many meadows. These changes were not confined to monitoring meadows within the port area but also occurred in the "control" meadows to the south of the port in Rodds Bay. An examination of the potential causes of the observed seagrass changes revealed that regional and local climatic events were the most likely driving factors of change, with port activity and developments unlikely to have had a significant impact between 2002 and 2004. Changes in seagrass were consistent with those in other areas of Queensland during the same time period, with the major changes in Gladstone probably due to high rainfall and localised flooding of waterways in February 2003. The changes to seagrass meadows had implications for local fisheries production especially the decline of highly productive intertidal Zostera capricorni meadows, which provide essential nursery habitat for juvenile tiger prawns. It was likely that these Zostera meadows had a good capacity for rapid recovery, should favourable environmental conditions return. Dugong continued to be active on the seagrass meadows near Wiggins Island and Fisherman's Landing in 2004 as evidenced by numerous feeding trails. Their presence and the extensive seagrass distribution in these areas had implications for the management of future port development. As this was the first of planned annual monitoring events we are still establishing the range of natural changes for seagrass meadows in the Port Curtis region. Continued monitoring will increase our ability to determine natural from human induced impacts on seagrass meadows as well as provide an ongoing assessment of the marine environmental health for the port. Despite being in its infancy the program is already beginning to reveal some of these trends and indicates that the marine environment of Port Curtis remained relatively healthy between 2002 and 2004