By indirectly controlling where dugongs feed, tiger sharks keep the seagrass mowed down at all areas.
"Dugong grazing can certainly hold seagrass growth in check," Wirsing explained.
If left unchecked, however, the herbivores would simply eat all of the seagrass.
"That's where tiger sharks come in," Wirsing explained.
Both tiger shark and dugong populations are at dangerous lows in many places, because of human influence.
People often fear tiger sharks, since they have attacked people in the past, but George Burgess, director of the University of Florida's International Shark Attack File, attributes the attacks to tourist recklessness. He said tourists may often "bring their aquatic recreation to places known to be sharky without asking natives about good and bad places."
World Conservation Society biologist Tim Davenport said the dugong situation is just as bad. He explained that "dugongs are now critically endangered" in certain regions, such as in Tanzanian waters, primarily due to a combination of fishing net entanglement and habitat destruction.
