Aretz et al_2011.pdf - ORBi - Université de Liège

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Kölner Forum Geol. Paläont., 19 (2011)
M. ARETZ, S. DELCULÉE, J. DENAYER & E. POTY (Eds.)
Abstracts, 11th Symposium on Fossil Cnidaria and Sponges, Liège, August 19-29, 2011
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and recurrence rate of disturbances, such as storms or cyclones that can cause physical damage to coralla,
but it is likely that on a given section of reef flat many nearby colonies of a given Acropora species could
represent clones. Hence, disturbance events causing fragmentation and resedimentation could in some
cases distribute branches of one genotype onto a colony of like genotype. Significantly, the coral branches
did not obviously appear to have been broken off of the host colony, although that is a possibility, but they
may have been transported laterally. Regardless, they were not washed off of the colonies subsequently.
Rather, they must have been held down, perhaps partly by interaction of the polyps in the underlying
corallum and or the branch. That soft tissues responded relatively quickly to the clast is suggested by the
fact that the broken end of the branches were not colonised by other benthos before they were overgrown
by new coral skeleton. Hence, soft tissues may have expanded over the broken branch ends relatively
quickly and this may help anchor the branches into place before skeletal fusion occurred.
Hence, we have demonstrated that live coral branches produced during a disturbance event may come
to rest on probable genetic clone colonies and become fused. The retention of branch fragments on colonies
in high energy reef flat settings suggests an active role of coral polyps to recognise and fuse with each
other. This ability may represent an adaptation to help heal damaged colonies where branches were
broken, but not removed from the host colony. Such an adaptation may be important for protecting
colonies from invasion by parasites and other benthos following disturbance events.
Fig. 1: A) Pebble clast of an Acropora branch encased with a cavity in another colony of Acropora sp. lined with
clypeotheca (arrows). B) Photograph of fused coral branch alive on the reef flat of Heron Reef. C) SEM image on a
polished and etched section of large amount of thickening deposits in the broken branch.
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