A comparison of taxonomic composition and diversity between reef coral life and death assemblages in Madang Lagoon, Papua New Guinea

The comparative taphonomy of reef coral life and death assemblages makes an important contribution in estimating bias in the taxonomic composition of fossil reef ecosystems. In Madang Lagoon, Papua New Guinea, the taxonomic composition of reef coral death assemblages shows varying degrees of congruence with adjacent life assemblages in fringing reefs. The original composition of coral communities from low energy reef crest sites appears to be more faithfully represented by their correspondent death assemblages than do those from high-energy reef crest sites where mixing of populations obscures the original coral composition. Coral death assemblages from low energy reef crest habitats may represent autochthonous deposits retaining some of the original community structure, whereas those from high energy reef crest habitats may represent detrital deposits retaining little of their original ecological information. In addition, coral zonation patterns appear to be better preserved at broad than local spatial scales. s richness, Shannon-Wiener index of diversity and evenness of life and death assemblages were constant between sites and depths in Madang Lagoon. For all three parameters, however, diversity of reef coral death assemblages is significantly less than that of the corresponding life assemblages. This may be due to the unique life history attributes of reef corals. The great longevity of many reef corals may exceed the amount of time needed to degrade their skeletons. Alternatively, only a subset of the life assemblage is being selectively incorporated into the death assemblage. hed measures of fidelity for non-reef marine environments are different from those found in the reefs of Madang Lagoon. In Madang Lagoon reef corals, many live taxa are not found dead, but most taxa in the death assemblage are found alive. The situation is reversed in shelly faunas from non-reef open marine, coastal and intertidal settings: most live taxa are found dead and few taxa in the death assemblage are found alive. As with the diversity results, this probably has to do with the unique life history of reef corals and/or selective preservation of a subset of taxa in the death assemblage. It may be, however, that the present study is not directly comparable to the other marine studies because (1) corals may undergo very different taphonomic processes from both reef and non-reef molluscs; and (2) the sampling regime of the present study, in targeting within- and between-habitat variability in preservation of taxonomic composition and diversity, may be different from previous studies. The community ecology approach utilized in the present comparative taphonomic study was sufficient to capture the high variability inherent in marine life and death assemblages.