Hermit Crabs and Rocky Shores

I’ve often thought that hermit crabs must be the most abused animals ever to find their way into captivity.  As members of that oft-used phrase ‘clean-up crew’ they are purchased in vast numbers to fulfill a role with little care or consideration.  What happens when there isn’t anything left to clean up?  I suspect many starve for want of adequate nutrition.

I’ve always had a soft spot for these amiable crustaceans, and first came across them exploring the rocky shores of the UK, where they are a constant and common component of the ecosystem.  My limited wanderings around the globe suggest that this is the case in warmer tropical seas as well, with rocky shores in the Indo-pacific seemingly littered with them, as you can see from these images.

As a diver I’ve often been surprised at just how hard it is to find hermits in the tropics.  I know they are there and I come across them frequently, but in nowhere near the densities that I find them in shallow waters.

A little digging online suggests that many hermits that enter reef tanks are more naturally shoreline dwellers where they can spend time grazing on rocks out of the water, which backs up my observations.

I suspect several factors play a role here: This is where algae-grazing molluscs are found and is thus where where hermits find their homes, and of course, rocky shores are rich with nutrients.  If you graze (or rely upon grazers, or do both), then there’s a good living to be made in the shallows.  Also, if you can survive some of the time out of the water, you can out compete species that cannot?