Urchins fighting?

[Angelwolf21203]

I'm wondering if there are certain species of urchins that will kill eachother? I just recently added a purple and white pincushion urchin which is about golfball size, and a smaller dime-sized black long spine to my tank. They are joining a larger longspine, also about goldball sized, and a small marble sized red tuxedo urchin. The two new additions just don't seem to be leaving eachother alone! It's almost as if the small long spine is trying to knock the pincushion over to get to it's underside. I separated them, turned the pincushion back right side up and moved the long spine away. They both went their separate ways, but about half an hour later the long spine was at it again! I pulled the pincushion out of the tank and put it in my sump, because there's a ton of algae down there anyway, and no one else to bother it. But I have never heard of this, before. Had anyone seen or heard about this?

 

[ichthyoid]

I was intrigued, looked into it & found the study below, which confirms aggression between urchins does occur.

That said, I have seen massive congregations of black spine (Diadema) urchins, numbering in the thousands in the out islands of the Bahamas. I don’t know if that was related to spawning, feeding, aggression or something else?

Aggression among sea urchins on Caribbean coral reefs

The existence and nature of intra- and interspecific aggression were examined for five species of sea urchins inhabiting Caribbean coral reefs. The st…

www.sciencedirect.com

 

[Angelwolf21203]

I was intrigued, looked into it & found the study below, which confirms aggression between urchins does occur.

That said, I have seen massive congregations of black spine (Diadema) urchins, numbering in the thousands in the out islands of the Bahamas. I don’t know if that was related to spawning, feeding, aggression or something else?

Aggression among sea urchins on Caribbean coral reefs

The existence and nature of intra- and interspecific aggression were examined for five species of sea urchins inhabiting Caribbean coral reefs. The st…

www.sciencedirect.com

Thanks for the info! I'm just thinking maybe because they are 2 different types. Interesting, either way, though. And I'm glad to have a sump so I can let the other one at least recover, and have plenty to eat.