Jonathan Martin usually studies fish, but on a diving trip earlier this month near Whytecliffe Park, he noticed dozens of dead starfish in the water.
The starfish, also known as sea stars, looked deflated, and many had lost limbs.
Martin says he isn't sure what's causing the die-off, but speculates a population boom could be a factor because an increased population leads to increased competition for food and also heightens the impact of disease.
Martin has reached out to other marine scientists around the world to help solve the mystery, including Christopher Mah, a research collaborator with the Smithsonian Institution National Museum of Natural History.
In his blog, Mah writes the die-off appears to be similar to starfish wasting disease. Martin is waiting to hear back from other researchers as well.
Martin recently shot a video (posted below) at the dive site near Kelvin Grove, and says similar scenes have been noted at Whytecliff Park and other popular dive sites.