Long-term seagrass monitoring in Cairns Harbour and Trinity Inlet: December 2009 and 2010
Other Publication ResearchOnline@JCUAbstract
This report details results from the October 2009 and October/December 2010 seagrass monitoring surveys 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 examines selected representative seagrass meadows in the area annually. 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. Results of the 2009 and 2010 monitoring surveys indicate that seagrass habitat in Cairns Harbour and Trinity Inlet was in a poor condition. Seagrasses were in a highly vulnerable state with meadows reduced to their smallest area and density recorded in the monitoring program. The large seagrass meadows adjacent to the Esplanade and on the opposite of the Inlet between Bessie Point and False Cape suffered major declines in seagrass, becoming patchy and fragmented with only light cover of seagrass within remaining patches. Density and distribution of other small monitoring meadows in the inlet was less affected. The large declines in seagrasses were likely associated with local and regional climate conditions of high rainfall, flooding of local catchments and low light conditions creating unfavourable conditions for seagrass growth. Such changes in Cairns were consistent with similar trends noted at other seagrass monitoring locations on the east coast of North Queensland over the same time period. While these climate conditions provide the likely explanation for seagrass declines, 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: • Assessing light and temperature at the meadow level (in situ loggers) • Examining reproductive and recovery capacity of the meadows • Expanding the geographic scope of the area examined to a broader region and incorporating additional monitoring meadows • Linking water quality assessment with seagrass condition 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 such as those that have occurred over the last two years may have had the capacity to reduce the resilience of seagrasses in the region due to compounding effects of current human activities such as urbanisation, coastal and port development. The vulnerable state of some seagrasses in Cairns underscores the value of continued monitoring to ensure the long-term viability of these marine habitats. While port activities during 2010 were unlikely to have had a major impact on seagrass condition, the current state of low resilience may mean that the seagrass is increasingly vulnerable to impacts to which they have previously been resilient and that there is a greater potential for activities within the Trinity Inlet catchment to influence seagrass condition. Extra vigilance should be maintained for any activity such as maintenance dredging, coastal development, land use change or runoff water quality that has the capacity to impact on water quality and seagrass condition, until these meadows have recovered.
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45
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Department of Employment, Economic Development and Innovation (DEEDI)
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Cairns, QLD, Australia
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