We tend to think of most corals as being stationary, one-sided colonies of creatures but in some habitats, an abundance of corals occur as living tumbleweeds. When colonial corals occur as unattached rolling living rocks they are called ‘rolloliths’ – while diving one particular site during the Fluval Sea Flores Expedition we observed an incredible diversity of coral genera living this way.
Just about a year ago we shared with you an unattached Goniopora colony from Australia which had tissue on all its side, and a case of aquarium grown red flowerpot corals which had also developed into free-rolling ball-shaped colonies. Previously the rollolith phenomenon had been documented in other, much tougher species of stony corals but we’re here to add a few more genera to that list.
The species of stony corals which are naturally tough in skeleton and grow into submassive shapes like Cyphastrea, Porites and Favites are not surprising to see growing into rolloliths. But the species which really surprised us when we encountered them in their tumbleweed form were unexpected species like Montipora and one particularly awesome looking piece of Pachyseris rugosa.
The rollolithic Montipora was only mildly branching in places but it just barely fit the bill as it did have tissue covering all of its surfaces and underside but the non-spherical shape prevents this colony from rolling too much in all but the strongest of current. The Pachyseris rollolith on the other hand was really cool looking, with the unique pattern of this coral species covering all sides of rounded colony making it look like some kind of strange living crystal.
Given the discovery of these unique living coral tumbleweeds, we wouldn’t be surprised to find just about any species of stony coral living as rollolith provided they occur in the right habitat with just the right amount of wave action and water motion. It’s easy to pigeonhole colonial stony corals as being benthic reef creatures, and while the majority of them are, corals can still surprise us with their resilience and adaptability to unconventional lifestyles.