High Ecological and Environmental Fidelity of Marine Benthic Fossil Assemblages

Ecological and environmental estimates derived from paleontological data may be distorted due to taphonomic biases and time averaging. To assess how well fossils preserve ecological and environmental information, we compared multi-taxic macroinvertebrate benthic communities (135 species from 6 phyla) with sympatric skeletal accumulations (death assemblages; 150 species) for 52 coastal sites in North Carolina (USA). The series of resulting studies indicate that death assemblages have high informative value, and their fidelity relative to living communities is remarkably robust. First, the assessment of live-dead faunal composition captured community organization along an onshore-offshore depth gradient. In multivariate ordinations Axis 1 locality scores correlated significantly with locality water depth, and taxon scores were concordant with the observed occurrences of taxon depths. Moreover, the live and dead datasets yielded consistent habitat delineations in multivariate ordinations. This direct test across modern sites with known bathymetry supports the use of multivariate proxies derived from benthic marine death assemblages as a quantitative proxy for water depth. In addition, dead mollusks were an excellent proxy for all taxa when tracking depth gradients. Second, although community composition differed between the live and death assemblages, these differences were predictable with an overabundance of phyla and classes with robust skeletons in death assemblages. Third, compositional spatial heterogeneity (beta diversity) did not differ significantly between live and dead whether using all organisms, only mollusks, or only non-mollusks. These congruent estimates suggest that mollusks alone can also serve as reliable surrogate community proxies for beta diversity. Finally, high live-dead fidelity is also supported by congruence in quantitative indices of functional diversity (functional richness, redundancy, and vulnerability), biological traits, overlap in multidimensional functional space, and species distributions among functional groups. That is, despite the overabundance of mollusks and other skeletonized taxa, the live and dead estimates of functional diversity were concordant. Consistent with previous work in other study systems, these results indicate that shallow marine death assemblages can yield robust ecological estimates adequate for assessing the historical variability of ecosystems. Despite filters imposed by differential preservation and time averaging, the fossil record is likely reliable with respect to relative comparisons of biodiversity and ecology across shallow benthic marine assemblages. The high spatial fidelity of death assemblages supports the emerging paradigm of Conservation Paleobiology that paleontological data can quantify anthropogenic changes in marine ecosystems and advance our understanding of spatial and temporal aspects of biodiversity.