[Header photograph by Ron Kroetz]

In true Halloween spirit, I would like to share this weird & spooky phenomenon that has been occurring in starfish all around the world for the past 70 years. Imagine watching a beautiful starfish in a rock pool moving slowly over crevices, and suddenly without warning, starts to tear its own arm off strand by strand. The detached arm thrashes around a little and seemingly with a mind of its own, crawls off into a dark corner.

Sea star wasting disease

However, this isn’t a scene from a zombie horror film; many starfish are succumbing to this awful fate. There have been several catastrophic mass die-offs globally with the most recent episode occurring in 2014 and scientists are understandably worried. You can watch an example of this horrifying phenomenon down below:

Youtube video by Stokeiometry

Turns out this phenomenon is caused by a virus called sea star-associated densovirus (SSaDV) and it causes what is known now as the sea star wasting disease or starfish wasting disease. This disease affects over 40 species globally and the increased incidences have been linked to the rising sea temperatures.

When a starfish becomes infected, the first visible symptoms are white lesions closely followed by tissue decay. The starfish becomes lethargic and limp as its water vascular system (similar to our blood circulation) starts to fail. After that its limbs start to stretch and detaches from the body and the starfish wastes away and dies. This can happen very quickly, with scientists noting death occurring 24 hours after the first limb falls off.

Starfish with severed limb | Photograph by Oregon State University

But what about the stories about starfish being able to regrow from a limb that has been cut off? Can’t these starfish just regrow themselves from those broken off arms?

Yes, there have been instances where starfish can regrow fully from a single detached arm. Some species decide to voluntarily give up an arm to escape a predator, and some even use this method to reproduce. But sadly, this isn’t the case here. Self-regeneration is only found in several species of starfish and for that to happen, part of the central disc of the starfish has to detach along with the arm and only then can a full starfish regrow from the severed arm. With this disease, the arms have fallen off because of decay and disease so these arms will end up dying. Lets hope scientists can come up with a cure soon or we will face increasing amounts of mass mortalities in the starfish population!