The Upper Rhaetian coral limestone of Adnet, southeast of Salzburg, Austria has been repeatedly referred to as one of the most spectacular examples of an ancient 'autochthonous' coral reef structure. The 'Tropfbruch' quarry is probably the best outcrop for interpreting the distributional patterns of biotic successions and communities of a late Triassic patch reef. Our study is based on the interpretation of a) outcrop photographs, b) reef maps resulting from quadrat transects, and c) the analysis of quantitative data describing the distribution and frequency of reef organisms and sediment. A new methodological approach (combination of reef mapping and photo-transects) is used to obtain quantitative field data which can be compared in greater detail with data from modern coral reefs investigated by corresponding quantitative surveys.  Three unconformities and three well-defined 'reef growth stages' reflecting the vertical and lateral development of the reef structure were differentiated using transects:  Stage 1, representing the reef growth optimum, is characterized by laterally differentiated coral reef knobs with corals in growth position. Criteria supporting this interpretation are the extraordinary size of the corals, their preservation in situ and the great thickness of this interval. The massive coral Pamiroseris grew under higher energy conditions at the rim of the reef knob, whereas branching Retiophyllia colonies preferred less agitated water in the center. Vertical changes are reflected by an increase in frequency of the dasycladacean alga Diplopora adnetensis and by the decreasing size of Retiophyllia. These sedimentological and biological criteria together with the unconformity above indicate a fall in the sea level as a major control mechanism.  Stage 2, separated from stage 3 by an unconformity caused by partial subaerial exposure and karstification, is characterized by vertically stacked coral successions with diverse reef debris. Facies heterogeneity is reflected by differences in the diversity, taphonomy and packing density of reef-building organisms as well as by differences in sediment input from the platform. Water depths and accommodation space were lower, therefore minor sea level fluctuations had a stronger effect on the biotic composition. The high percentage of coral debris and corals reworked by storms and the increase in the input of platform sediment led to a reduction of reef growth.  Stage 3, again separated at the base by an unconformity associated with karstification, is characterized by bioclastic sediments with isolated reefbuilders forming a level-bottom community. The distribution of different coral morphotypes suggests that sea level fluctuations were not the only controlling factor. Variations in the substrate were caused by differences in the input of platform sediment.  The vertical changes in reef community structures correspond to a sequence of 'allogenic replacements', because the change from one community to another is the result of extrinsic environmental factors (short-term subaerial exposure of parts of the reef structure and renewed flooding). Our new data provide no support for the model of ecological reef successions to the Adnet reef. The three-step development seen in Adnet documents the response of low-diverse coral associations to variations caused by small-scale sea level changes, storm activity and sedimentation.  The distribution of communities as well as the vertical development of the Adnet reef structure offer no general model of Alpine Upper Rhaetian reefs, because of the particular setting of the patch reef (platform reef surrounded by calcareous sands). Only the 'capping beds' of the Upper Rhaetian Reef Limestone of the Steinplatte exhibit criteria similar to Adnet (high coverage of spatially separated Retiophyllia A and Retiophyllia B communities, strong inpact of freshwater dissolution pointing to subaerial exposure and small-scale karstification).  Potential modern analogues of features seen in the coral communities of Adnet are the internal structure of the Retiophyllia thickets, the key role of branching corals within the communities, the scattered distribution and low and even diversity of corals subsequent to breaks in settlement, segration patterns of corals indicating 'contact avoidance', toppling of large coral colonies by intensive boring, and decreasing coral coverage from deeper and sheltered settings to more shallower water depths.