Port of Townsville long-term seagrass monitoring: October 2011
Other Publication ResearchOnline@JCUAbstract
This report details results from the fourth annual seagrass monitoring survey for Townsville Harbour and discusses changes in inter-annual seagrass meadow dynamics. The annual seagrass monitoring program is used to assess the health of the Townsville's marine environment by using seagrasses as a key indicator of environmental health. The program provides an annual update of the health and resilience of these key fisheries habitats to the Port of Townsville Limited (PoTL) to inform their port development and maintenance programs and 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. Results of the 2011 monitoring survey indicate that seagrasses in Townsville are in a highly vulnerable condition. While some seagrass meadows showed small signs of recovery in density compared to 2010, seagrasses generally remained at their lowest distribution and lowest density since the baseline survey in 2007. The declines seen throughout the monitoring meadows have occurred across both intertidal and subtidal regions. The greatest losses were recorded in the meadows at Cape Cleveland and the subtidal Pallarenda meadow which had reduced to a small remnant patch of seagrass. Additionally, there has been a gradual shift in the species composition of many meadows to be comprised of a greater amount of the smaller pioneering Halophila species. The large declines in seagrass were likely associated with local and regional climate factors including high rainfall, flooding and a reduced light environment creating unfavourable conditions for seagrass growth. Similar declines in seagrasses were found in Cairns, Mourilyan and Gladstone indicating a regional rather than local driver of change. While climate patterns were correlated with seagrass declines, a lack of environmental data at the meadow scale makes interpretation of observed changes difficult. A better understanding of environmental influences on the Townsville seagrass meadows would greatly enhance the existing monitoring program, including information recorded on the actual conditions seagrasses experience within the meadow, rather than inferring conditions from regional climate information. Light and temperature are two of the major factors that have been linked to changes in seagrass, as has been shown for monitoring meadows at other locations. The investigation of these two environmental parameters could potentially be incorporated into the Townsville monitoring program. The seagrass meadows of Townsville 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 (Rasheed et al. 2007). Persistent and natural climate events such as above average wet seasons over the previous two years have affected the resilience of local seagrasses. The vulnerable state of seagrasses in Townsville underscores the need for continued monitoring feeding into management of human activities to ensure the long term viability of these marine habitats. While port activities including capital development and maintenance are not the only threat, they are activities that can be managed in a way that minimises any additional pressure on seagrasses. The results of this program form part of the assessments of annual maintenance dredging through the Townsville Dredge Technical Advisory Consultative Committee (TACC), where planned dredging is critically reviewed to establish if any additional management measures are required. The vulnerable condition of seagrasses warrants extra consideration of the scale and duration of maintenance dredging, capital works and port operations in proximity to these seagrass meadows to ensure their continued capacity for recovery. While this is an excellent step toward protecting seagrasses, critical assessment and continued improvement to management of other activities such as Urban and Industrial runoff and improvements to non-point source impacts such as agricultural runoff into nearby catchments is also needed to ensure the best long term outcome for the regions seagrasses.
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35
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Department of Employment, Economic Development and Innovation (DEEDI)
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Cairns, QLD, Australia
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