Hard corals are often thought of as largely inanimate, stony creatures, incapable of all but the smallest movements, but despite this both scientists and aquarists have noticed that some seem capable of rescuing themselves from burial by sand.
Until now, no one knew quite how they managed this trick, but thanks to time-lapse photography used for the videos below, we now have the answer.
Dr Pim Bongaerts from the University of Queensland, deliberately buried specimens of Lobactis scutaria (Mushroom coral) and Herpolitha limax (Tongue coral) with sand in an aquarium and then filmed their reaction.
Unlike their more familiar branching coral cousins, these flattened, seemingly sedentary Cnidarians have a considerably thicker fleshy layer of tissue on top of their hard calcium carbonate skeleton, and time-lapse techniques revealed how this was used to push the sand away.
By photographing the buried coral every 10 seconds over a 20-hour period Dr Bongaerts showed that the sand was moved through a series of rhythmic pulses produced by the coral as it inflated and deflated its soft tissues.
Fungiid corals such as these are often found on the sea floor and are not physically attached to the limestone structure of the sea bed like most corals. This allows them to move themselves slowly around to find better habitat, but this active lifestyle leaves them at risk from burial by shifts in sandy sediments of the sea bed, particularly during storms. Now thanks to this unique insight we are able to witness the surprising level of control that these colonial creatures can muster in the face of potentially deadly adversity.
For more information see the paper; P. Bongaerts, B. W. Hoeksema, K. B. Hay and O. Hoegh-Guldberg 'Mushroom corals overcome live burial through pulsed inflation'; Coral Reefs (2012) DOI: 10.1007/s00338-011-0862-z
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