The nature of information loss in the paleoecological reconstruction of benthic macrofaunal communities using faunal assemblages from the recent Texas coastal environment

Abstract

The living benthic communities and their death assemblages at two locations on the Texas coast were studied in detail to determine their taxonomic and structural variability so that the processes by which organisms are incorporated into the death assemblage might be understood as well as the extent to which the death assemblage provides information about the original community. The death assemblages were analyzed as paleocommunities to determine the minimum estimate of the amount of data loss and distortion that should be expected in the formation of a fossil assemblage from the original living community. Temporal variability in the living communities was attributable to seasonal and salinity changes in the physical environments at the study sites of Aransas River and Padre Island. The death assemblages did not reflect changes of the magnitude observed in the living communities at either location during the study. The major taphonomic processes that altered the original community data were; differential preservation of faunal, physical and biological addition and removal of fauna from the death assemblage, and predation. Time-averaging in concert with taphonomic processes, and bioturbation condensation of shells produced death assemblages that were very dissimilar to the original communities or the preservable components of the original communities. Taxonomic composition, diversity and equitability measures and trophic proportions were examined and the differences between the living community and the death assemblage data were quantified. Death assemblage analysis incorrectly indicated that the physically more stressed living community at Aransas River was more diverse and equitable than that of Padre Island. The impact of time averaging was greater at Aransas River because the death assemblage was a composite of the taxa from the living, low salinity community and the taxa from a previous high salinity community. The death assemblage, while making paleocommunity analysis uncertain, provides a modern ecological tool for learning about past enviromental extremes. Detailed study of a variety of benthic assemblages is needed to gain a graphic understanding of and to compensate for data loss and distortion in paleocommunity equivalents which will make paleocommunity reconstruction more accurate.