Long term seagrass monitoring in the Port Curtis western basin: quarterly seagrass assessments & permanent transect monitoring progress report: November 2009 to November 2012
Other Publication ResearchOnline@JCUAbstract
Key Findings: • Long-term monitoring at permanent transects revealed that seagrasses in the Western Basin and Rodds Bay underwent distinct seasonal changes as well as significant inter-annual changes in seagrass distribution, abundance and species composition. • Over the duration of the monitoring program (since November 2009), Gladstone has received higher than average rainfall in the past three consecutive wet seasons, punctuated by two of the worst flood events on record. • Significant declines in seagrass abundance occurred at all sites during the monitoring program, particularly following the 2010/2011 floods. Some sites have shown substantial recovery, particularly in the outer harbour; however inner harbour sites have yet to recover to pre-flood levels. • Inner harbour sites were particularly impacted by the floods with many sites losing all seagrass cover. These sites have shown initial recolonisation in subsequent growing seasons, but abundance has declined each senescent season to very low levels. Increased rainfall and flooding and an associated decrease in Photosynthetically Active Radiation (PAR) reaching seagrasses was strongly correlated with the declines in seagrass abundance. • During 2011 seagrass C:P, N:P and C:N ratios plummeted at all sites in the inner and outer harbour, indicating that seagrasses were existing in a nitrogen limited, low light and nutrient rich environment. This was most likely associated with very high rainfall and river flow events in early 2011 bringing large volumes of highly turbid water and increased nutrients to the system. • Seed banks for Halophila ovalis and Zostera capricorni were detected at some locations in the harbour from which recovery could be initiated when conditions are favourable for germination, seedling survival and for subsequent clonal growth and colonisation. • Gladstone seagrasses were capable of rapid clonal growth and the production of flowers, fruits and seeds. However this varied substantially between meadows and time of year. It is likely that propagule limitation at some sites may be inhibiting seagrass recovery. • It is estimated that the major area of dense seagrass in Gladstone, the intertidal Zostera capricorni meadow at Pelican Banks, incorporates up to 0.63 grams of carbon m⁻² day⁻¹ into its above-ground biomass, which translates to more than 4 tonnes of carbon per day for the meadow at peak distribution and density.
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13/16
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93
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TropWATER, James Cook University
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Cairns, QLD, Australia
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