This project has investigated the responses of the seagrass Posidonia sinuosa to light reduction with the aim of understanding its response mechanisms and to identify characteristics that could form appropriate monitoring indicators. Shoot density reductions have been the most consistent response observed down depth-related light gradients and in response to imposed shading. While some morphological and physiological differences were also observed, they were highly variable and the most pronounced in conditions of severe light reduction. P. sinuosa can survive considerable periods at only 9% ambient light availability with 8% of shoots still remaining after 206 days.
Posidonia sinuosa shoot density during control, light (88% of ambient), moderate (28%) and heavy shading (9%) and the following recovery period in Cockburn Sound. After 3 months of shading, 84% of shoots were lost in the heavy shade. Recovery was considerably faster in moderate shade, but was still significantly less than the controls after 384 days in ambient light.
Following a brief (2 hour) incubation of a mature leaf (ML) with 13C, the concentration in the young leaf (YL) and the adjacent rhizome was monitored for 4 weeks to determine whether internal nutrient cycling can prolong shoot life when shaded. Percent of the 13C in the ML declined as it was exported to the YL and rhizome which contained 44% and 20% of that taken up by the ML, respectively and was not significantly affected by shading.
Professor Paul Lavery
Department of Environment and Conservation, Ray Masini
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