Microbial loop carbon cycling in ocean environments studied using a simple steady-state model

RJ Orth
KL Heck
DJ Tunbridge


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 R 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.