Deepwater seagrass dynamics: light requirements, seasonal change and mechanisms of recruitment for deepwater seagrasses: interim report
Other Publication ResearchOnline@JCUAbstract
[Extract] KEY FINDINGS This interim report provides a progress update from a long term study into the drivers and dynamics of tropical deepwater seagrasses (>10m). This is the first detailed study of its kind in Australia. Key results to date include: • Deepwater experimental sites have been established at three locations along the Queensland coast (Mackay, Green Island and Lizard Island) and regular (at least quarterly) sampling has shown differences in the species composition, abundance and seasonal patterns of recruitment and senescence among these deepwater seagrass communities. • Halophila decipiens was found at all three locations, while Halophila ovalis, Halophila spinulosa and Halodule uninervis were also present at the Lizard Island site. • Early results indicate there may be latitudinal differences in the extent of seasonality for deepwater seagrasses, with seagrasses more persistent throughout the year in the Far North and becoming annual with a short growing season to the south. • At Green Island, Halophila decipiens displayed a distinct pattern of seasonal recruitment and senescence, recruiting in later winter to early spring and senescing over the summer months. At Lizard Island and Mackay, the precise timing of recruitment and senescence is still being investigated but abundance appears to peak around November, similar to Green Island seagrasses. • Halophila ovalis, the dominant species at Lizard Island, was present year round with peak abundance (percent cover and shoot density) around November. • Intra-annual trends in seagrass abundance are likely driven by the availability of Photosynthetically Active Radiation (PAR) but water temperature may also play an important role in driving recruitment and senescence. • PAR was generally lower and more variable at the Mackay site than at Green Island and Lizard Island sites and may explain the very low abundance of seagrass detected at the site; however propagule supply is likely another major factor. • Significant Halophila decipiens seed banks have been identified at both the Green Island and Lizard Island sites whilst no seeds have been found in the sediments at the Mackay site thus far. Care needs to be taken in the interpretation of these results as they are initial findings only. More definitive results will be developed with longer term data sets during the course of the program and as the results of the laboratory manipulations become available.
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13/20
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29
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TropWATER, James Cook University
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Cairns, QLD, Australia
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