As I mentioned earlier, I was fortunate enough to visit Exmouth and Coral Bay to see a variety of marine life, and the reason for the marine life is because of the amazing coral reefs. Not far south from Coral Bay is the Shark Bay Marine Reserve - this reserve has the largest abundance of seagrass in the world - in fact it has 112 known species of sea grass. I visited Shark Bay in December last year, and while I was there for two days, I saw dugongs, turtles, rays, two tiger sharks and at least 40 nurse sharks.
Dugongs, turtles and rays all feed on seagrass. Dugongs eat seagrass like a large hand ripping grass from the roots; they change the structure of the seagrass beds. Rays eat seagrass the same way, but on a smaller scale and turtles, they nibble on the seagrass blades. Sharks protect seagrass by keeping dugongs, turtles and rays at bay, moving them on from the area.
A study in North Carolina, where sharks had been fished out of the area, saw in increase in rays. Apart from seagrass, rays also predate on bivalves (scallops, clams, oysters - the hard-shelled seafood). In 2004, this saw a century old scallop industry collapse ... which is bad news for commercial fisherman!