Freiwald A, Roberts JM (eds), 2005, Cold-water Corals and Ecosystems. Springer-Verlag Berlin Heidelberg, pp 937-977 Shallow-water Desmophyllum dianthus (Scleractinia) from Chile: characteristics of the biocoenoses, the bioeroding community, heterotrophic interactions and (paleo)- bathymetric implications Günter Försterra 1,2 , Lydia Beuck 3 , Vreni Häussermann 1,2 , André Freiwald 3 1 Departamento de Biologia Marina, Universidad Austral de Chile, Avda. Inés de Haverbeck, casas 9, 11 y 13, Campus Isla Teja, casilla 567, Valdivia, Chile (gunter_forsterra@yahoo.com) 2 Department Biologie II, Ludwig-Maximilians-Universität München, Karlstr. 23- 25, D-80333 München, Germany 3 Institute of Paleontology, Erlangen University, Loewenichstr. 28, D-91054 Erlangen, Germany Abstract. We report an unusually shallow-water occurrence of habitat-forming Desmophyllum dianthus (Esper, 1794) from the Chilean fjord region. Most occurrences of the cosmopolitan D. dianthus are known from the bathyal zone. In the northern Chilean fjord region, however, this coral is reported within the euphotic zone. The upper limit of distribution was found at 7 m water depth and is confined to the lower boundary of the low salinity layer. Large accumulations both as living aggregations and as sediment-formers typically occur from 20 m water depth and beyond. The corals prefer to colonise the undersides of rock ledges with downward- facing corallites. The motivation of this study is to analyse and discuss the existence of an azooxanthellate coral that generally thrives in aphotic environment but here extends into the photic zone by means of screening of bioerosion patterns. Based on the detailed analysis of scratching and boring traces, we compare the ichnocoenosis found within the Chilean D. dianthus with the established bathymetrically indicative ichnocoenoses from other areas around the world. These indicator ichnocoenoses are widely used to reconstruct relative water depths of depositional settings in the geological past. The study of the bioeroding assemblage from two living D. dianthus collected at 28 m water depth in the Reñihue Fjord, Chile, shows some remarkable patterns that shed light on the complex way in which the coralʼs soft tissue expands and retracts at the apical zone of the corallum in response to in vivo infestation of endolithic algae. The role of this heterotypic interaction is discussed. To visualise the endolithic ichnocoenoses, we applied several methodologies such as the vacuum cast embedding technique combined with scanning electron