A few months ago, a worker at Crandon Marina on the northern tip of Key Biscayne noticed a strange-looking seagrass on the floor of Biscayne Bay. When Florida International University marine scientist Justin Campbell got a look at it, he identified it as strange indeed — a nonnative species from the Indian Ocean called Halophila stipulacea. The grass is short, with broad blades, and extremely hardy, Campbell said.