Coral-bryozoan mutualism: structural innovation and greater resource exploitaton.

Shell-encrusting species of the coral Aulopora and the bryozoan Leioclema changed ecological pgilds and escaped limits imposed by substrate size through mutstic intergrowth during the Early Devonian. Where colonies of these species intergew, they produced upright, arborescent masses consisting of sparsely branched uniserial Aulopora sp. entirely covered, except for calyx openings, by a thin encrustation of Leioclema sp. These interrowts appear to constitute a mutualistic association with benefits induding escape from limited space on the substratum into a higher tier of suspension feeders, as well as more modules per colony. Such mutualism between benthic modular competitors may have developed more readily than assocations between solitary competitors.