Port of Weipa long term seagrass monitoring: September 2009
Other Publication ResearchOnline@JCUAbstract
This report details results of the September 2009 seagrass monitoring survey in the Port of Weipa and discusses changes in inter-annual seagrass meadow dynamics since monitoring began in 2000. 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 monitoring found seagrasses in the Port of Weipa to be in a reasonable but vulnerable condition. Seagrass changes observed were likely to be associated with natural shifts in tidal exposure combined with changing light and temperature associated with local climate. These conditions have led to several meadows showing a long term declining trend. This trend has been of particular concern for Enhalus acoroides meadows, especially the large intertidal meadow opposite Lorim Point, where biomass reached a record low in 2008. The declines have likely left some meadows in a highly vulnerable state with a low resilience to further natural or anthropogenic impacts. In response to the declines North Queensland Bulk Ports (NQBP) and Fisheries Queensland conducted an additional survey of the intertidal Enhalus acoroides meadow in April 2009 to assess if the meadow was in a healthier state at times outside of the regular annual September survey. The April 2009 assessment showed an increase in seagrass from the previous September but biomass still remained significantly lower than for other assessments that have occurred in April (2000-2002). By the following September (2009), the meadow had once again declined to a similar low level recorded the previous year. Not all meadow types in the Port declined with some intertidal Halodule meadows significantly increasing in biomass from 2008 and 2009 and despite the changes observed in seagrass density, the distribution and area for most meadows remained similar to previous years. Seagrasses appear to have been resilient to the impacts associated with regular port maintenance dredging during the life of the current monitoring program. However, Fisheries Queensland remain concerned that the continued low density of some of the meadows in Weipa leaves them particularly vulnerable to additional stresses including those associated with dredging. Further enhancements to the established seagrass program including an examination of light and temperature conditions at vulnerable seagrass meadows would significantly enhance the ability of the program to pinpoint the causes of seagrass declines. An additional seasonal survey of the Enhalus meadow opposite Lorim Point in April 2010 may also be warranted. These measures would provide added assurance of the seagrass meadow's tolerance and capacity to withstand additional stresses. Fisheries Queensland and NQBP will be working on incorporating some of these measures into the long term monitoring program.
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29
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Department of Employment, Economic Development and Innovation (DEEDI)
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Cairns, QLD, Australia
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