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Marine Ecology Progress Series

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MEPS 394:21-33 (2009)  -  DOI:

Interactive effects of timing, intensity and duration of experimental shading on Amphibolis griffithii

Paul S. Lavery1,*, Kathryn McMahon1, Michael Mulligan2, Andrew Tennyson1

1Centre for Marine Ecosystems Research, Edith Cowan University, 270 Joondalup Drive, Joondalup WA 6027, Australia
2Geraldton Port Authority, PO Box 1856, Geraldton WA 6531, Australia

ABSTRACT: The responses of the seagrass Amphibolis griffithii to different experimental shading conditions were examined by characterising biomass, morphological and physiological features. In an in situ experiment, the intensity (ambient, moderate shading [13 to 19% of ambient] and high shading [5 to 11% of ambient]), duration (3, 6, 9 mo) and timing (post-summer, post-winter) of light reductions were manipulated. We observed interactive effects of all 3 factors, the most notable being with timing. When moderate shading was imposed at the end of summer there was a 57% loss of leaf biomass and 67% loss of rhizome carbohydrates within 3 mo. The same shading imposed at the end of winter caused no loss of leaf biomass and only a 25% decline in rhizome carbohydrates. This contrasting effect of time reflects the plant’s photo-physiological characteristics under the water temperature and light conditions. More prolonged or higher intensity shading produced more consistent responses at both times of year: moderate shading resulted in more than 93% loss of leaf biomass after 9 mo and high intensity shading resulted in more than 99% loss after 9 mo. The results highlight the importance of time of year when attempting to predict seagrass responses to shading. The study identified 14 potential early indicators of light reduction; these included leaf δ15N, which may reflect changes in the allocation of nitrogen in the photosynthetic apparatus. There is no evidence that A. griffithii is more susceptible to shading than larger seagrasses such as Posidonia spp.

KEY WORDS: Light reduction · Dredging · Seagrass disturbance · Australia

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Cite this article as: Lavery PS, McMahon K, Mulligan M, Tennyson A (2009) Interactive effects of timing, intensity and duration of experimental shading on Amphibolis griffithii. Mar Ecol Prog Ser 394:21-33.

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