Port Curtis and Rodds Bay seagrass monitoring program: November 2011
Rasheed, M.A., Reason, C.L., McCormack, C.V., Chartrand, K.M., and Carter, A.B. (2012) Port Curtis and Rodds Bay seagrass monitoring program: November 2011. Report. Department of Agriculture, Fisheries and Forestry (DAFF), Cairns, QLD, Australia.
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Abstract
This report details the findings of the November 2011 annual seagrass monitoring survey of Port Curtis and Rodds Bay. The report incorporates seagrass meadows monitored annually since 2002 as part of the Port Curtis Integrated Monitoring Program (PCIMP), as well as additional seasonal mapping of seagrasses within the entire Western Basin region of the port conducted every 6 months since 2009 as a part of increased monitoring for harbour expansion and dredging programs. The report integrates 2011 survey data with previous long-term monitoring surveys, assessing seagrass meadow area, biomass and species composition. The 2011 survey included an assessment of intertidal and shallow subtidal meadows in the Western Basin region from The Narrows to Boyne River, as well as long-term monitoring meadows located in Rodds Bay.
In November 2011 the total area of seagrass mapped in the Western Basin region was similar to November 2010 but well below the broad distribution mapped in November 2009. Biomass decreased in five of six regions between 2010 and 2011 (The Narrows, Fishermans Landing, Quoin Island, South Trees and Rodds Bay). The regions with the largest biomass reduction were Fishermans Landing and Quoin Island, where biomass decreased at 50 percent of sites. Of the fifteen PCIMP long term monitoring meadows, only eleven had any above-ground seagrass present during the survey. The subtidal meadow at south Fishermans Landing was absent for the second consecutive year and the Rodds Bay meadows were also absent. Of the monitoring meadows that were present most were similar in total area and biomass to November 2010 but lower than historical peaks.
The major driver of seagrass change is likely to be climate related as similar declines have been observed state-wide following a significant wet season in late 2010 to early 2011. Higher than average rainfall and river flow with subsequent decreases in light are suggested as some of the major drivers of seagrass dynamics in the Port Curtis area. Should climate conditions become more favourable to seagrass growth we would expect to see recovery of these seagrass meadows.
Since late 2009, assessments of light and temperature have begun to provide information on in situ conditions to evaluate changes occurring at the meadow scale. Long-term collection of such data within meadows will enhance the effectiveness of the monitoring program by distinguishing some natural versus anthropogenic drivers of seagrass change. Low light levels at a number of meadows suggest seagrass may already be subject to light stress, reducing their potential resilience to future impacts. The light data collected during 2011 supports a reduction in available light being one of the primary causes of seagrass decline at many meadows.
The scale of loss at some meadows has left the seagrasses of Port Curtis in a condition where they may be vulnerable to additional stresses including those associated with dredging. A more complete understanding of the environmental requirements of seagrasses in Port Curtis is being developed as part of additional seagrass studies connected with the Western Basin development (Chartrand et al., 2012). These studies will help to accurately inform the environmental management of port developments and ensure management triggers are related to the ecological requirements of local seagrasses.
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