Long Term Seagrass Monitoring in the Port of Mourilyan - November 2006

This report details results from the November 2007 seagrass monitoring survey for the Port of Mourilyan, conducted as part of the annual long term monitoring. The monitoring program was developed following a baseline survey in December 1993 and examines selected representative seagrass meadows in Mourilyan Harbour. Total area of each monitoring meadow, species composition and seagrass density (above-ground biomass) were measured for comparison with previous surveys. The survey found seagrasses were generally well below their peak density and biomass, with many meadows remaining in a highly vulnerable state. However, there were some positive signs with the high-density Zostera capricorni meadow remaining in a relatively healthy condition, the re-establishment of an intertidal Halophila meadow that had been lost in 2006 following Tropical Cyclone Larry, and a significant increase in biomass for the main subtidal seagrass meadow. Despite this, concerns remain for the other intertidal meadows that have become sparse and highly fragmented in recent years and are likely to have low resilience to further stress. The recent changes to seagrass meadows at Mourilyan Harbour are most likely a result of a combination of regional climate, severe storms and localised catchment issues rather than port-related activities. However the reduced resilience of these meadows makes them potentially more vulnerable to additional impacts including those associated with port and harbour operations and developments. This most recent survey should "raise a warning flag" for increased scrutiny of Mourilyan Harbour's marine environment. Should future surveys show a continued deterioration of seagrass condition, a close examination of water quality issues in the catchment may be warranted.