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Marine Ecology Progress Series

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MEPS 244:81-88 (2002)  -  doi:10.3354/meps244081

Predation on seeds of the seagrass Posidonia australis in Western Australia

Robert J. Orth1,*, Kenneth L. Heck Jr.2, David J. Tunbridge3

1Virginia Institute of Marine Science, School of Marine Science, College of William and Mary, 1208 Greate Road, Gloucester Point, Virginia 23062, USA
2Dauphin Island Sea Laboratory, University of South Alabama, 101 Bienville Boulevard, Dauphin Island, Alabama 36528, USA
3Marine and Freshwater Research Laboratory, School of Environmental Science, Murdoch University, PO Box 30, Murdoch, Western Australia 6150, Australia

ABSTRACT: Despite much evidence that predation governs seed abundance, and ultimately seedling and adult plant distribution and abundance in terrestrial ecosystems, there is a dearth of information from seagrass dominated ecosystems. We report here on the first study to examine predation rates from seeds of Posidonia australis measured during field tethering experiments at 5 locations in Western Australia. Seeds that were recently dehisced from ripe fruits and at a similar stage of development were tethered in seagrass and adjacent unvegetated sand for 24 h and then assessed for damage. Seed predation was noted at all sites and ranged from partially to completely eaten seeds. Higher daily proportional damage was observed in seagrass (34 to 53%) than on unvegetated sand (3 to 20%), but was significantly greater at only 3 of the 5 sites. There was no significant difference in proportional mortality for seeds among seagrass meadows, whereas in sand, there was a significant site effect. While we were unable to identify specific seed predators, the type of damage we observed on the seeds suggest small fish or invertebrates are the primary causative agents. Our results add to the growing body of evidence that seagrass seed predation does occur, that it has the potential to affect recruitment, and has implications for understanding the dynamics of P. australis meadows. Finally, our data present an interesting contrast to the paradigm for seagrass faunal studies, which almost invariably have shown higher proportional mortality in bare sand than in seagrass.

KEY WORDS: Seeds · Seagrass · Predation · Posidonia australis · Western Australia · Tether

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