Seagrass seed dispersal by marine mega-herbivores: Dugongs (Dugong dugon) and green sea turtles (Chelonia mydas)

Marine mega-herbivores, such as dugong (Dugong dugon) and sea-turtles (Chelonia mydas), are known to move 100s of kilometres within short time frames and are almost obligate seagrass consumers. Consequently, they may be an... [ view full abstract ]

Marine mega-herbivores, such as dugong (Dugong dugon) and sea-turtles (Chelonia mydas), are known to move 100s of kilometres within short time frames and are almost obligate seagrass consumers. Consequently, they may be an important long distance disperser of seagrass seeds, contributing significantly to meadow connectivity and re-establishment after loss. If so, it is important to quantify the role they play in facilitating seed dispersal. This is only true if they consume significant numbers of seeds and these seeds remain viable after passing through their gut. Therefore, we studied the potential role of two different mega-herbivore species in seagrass seed dispersal by examining seed viability after gut passage. Dugong faecal samples were collected from three intertidal seagrass meadows within the northern Great Barrier Reef (Whitsundays to Townsville) during the peak period of seagrass reproduction from September to December 2014. Sea-turtle scats were also collected from two individuals held in a rehabilitation centre that had been fed seagrass seeds of a single species. Seeds of four seagrass species were found to traverse the digestive tract in dugongs. The single species of seagrass seeds fed to turtles also passed though their digestive tract with minimal damage. Tetrazolium staining of the seeds recovered from dugong faecal matter showed that close to 10 percent of seeds passed were found to be viable. A small number of seagrass seeds had also begun to germinate within the dugong faecal matter before staining. Our results demonstrate that biologically significant numbers of viable seeds can be transported and dispersed by marine mega-herbivores; suggesting that this mode of dispersal needs to be considered when trying to understand the processes determining seagrass population stability and re-establishment dynamics.