Port of Townsville long-term seagrass monitoring: September 2012

This report details the latest results from the annual seagrass monitoring program for the Port of Townsville conducted in 2012. Results of the program are used to assess the health of the marine environment in the Townsville region and the port by using seagrasses as a key indicator of environmental health. The program provides an annual update of seagrass health and resilience to the Port of Townsville Limited (PoTL) to support ongoing management of port operations and planning for port developments. Annual monitoring in Townsville also forms part of a network of seagrass monitoring programs established throughout Queensland looking at the status and condition of seagrasses in the highest risk areas of the State. Key Findings • Seagrasses in Townsville had shown significant recovery in area and density during 2012 after several years of decline. • While many meadows had seen the return of "foundation species" much of the newly recolonised areas were still dominated by initial colonising species such as Halophila. • Townsville was one of the few coastal areas in the Wet and Dry Tropics regions where seagrasses have shown significant recovery in 2012. • Evidence of dugong feeding was observed in many meadows and a large herd of dugong (estimated more than 100) were observed feeding on seagrasses in Cleveland Bay during the monitoring survey. • The observed seagrass increases are a promising sign, however meadows remain vulnerable to further natural and anthropogenic impacts as recovery was still incomplete and meadows were likely to have a reduced resilience following several years of decline. In 2012 Townsville's seagrasses had begun to recover from the declines in abundance and distribution recorded over the last four years. Prior to 2012, Townsville seagrasses were impacted by regional scale climate events that saw similar declines to seagrasses in other areas of tropical eastern Queensland including, Cairns, Mourilyan, Bowen/Abbot Point and Gladstone. Townsville was one of the few locations where coastal seagrasses have shown significant recovery. All but two of the ten monitoring meadows showed substantial increases in meadow area and every meadow increased in biomass. There was also a shift in the landscape category of many meadows, with several changing from isolated patches of seagrass to aggregated patches and many previously fragmented sections of meadows re-joining in 2012. The increase in area for the dense Zostera capricorni meadow in Cleveland Bay was particularly encouraging. However, much of the newly re-established sections of meadows remained dominated by small pioneering species from the genus Halophila. It was likely an increase in the light available for growth and photosynthesis of seagrasses contributed to the observed recovery, through a combination of tidal conditions and a reduction in rainfall and flooding and associated reduction of turbidity. While local weather patterns were correlated with seagrass recovery, a lack of environmental data at the meadow scale makes interpretation of observed changes difficult. The addition of water quality monitoring and in particular light and temperature within the seagrass canopy at monitoring meadows would greatly enhance the existing monitoring program. Although seagrasses have shown significant recovery in 2012, several consecutive years of decline have placed seagrasses in a vulnerable state from which it has not fully recovered, with meadows likely to have a reduced resilience to further impacts. Managing human activities and impacts and monitoring the continued condition of seagrasses will be critical to ensure seagrasses have the opportunity to fully recover and in maintaining the long-term viability of these marine habitats