mutualism b/w octos and hermit crabs?

[anat.incor.octo]

hi...i'm a new member!
right now i'm in South Caicos (Caribbean) taking a marine ecology class. for the past few weeks i've been checking up on a caribbean reef octopus that lives near the school's dock. i had only seen him inside his den up until last night when i finally saw him half out of it. unfortunately, my dive light scared him back inside, but as i watched, i realized he wasn't the only guy in the neighborhood. at least 20 hermit crabs were crawling in and around his den, at one point even completely blocking the entrance for a good 20 minutes. i have never seen so many crabs at once before, much less around a predator's den!
i assume they were there scavenging empty shells from the octo's latest meal (of which there are always many scattered about), but still i was surprised--i have never heard of anything like it!
can anyone shed some light on this?
thanks!

 

[Taollan]

I have noticed this as well with the giant Pacific octopus, and in fact there is a whole host of organisms that will be living in a GPO's midden, including hermit crabs, umbrella crab (cryptolithodes), and many snails. There is a paper on this relationship in GPO dens that includes many other associates such as sculpins and starfish:

Hartwick EB, Thorarinsson G (1978) Den associates of the giant Pacific octopus, Octopus dofleini (Wulker). Ophelia 17(1):163-166

I hope this helps out a little bit.

 

[Fini]

They probably love the Octo's leftovers being the messy eaters they are.