Paleontological data can provide historical perspective that is inaccessible in modern ecological studies, but progressively in demand in the face of rapidly changing climate and environmental degradation. Studies quantifying the mismatch between living communities and concurrently accumulating death assemblages across multiple phyla are therefore essential in assessing the quality of the fossil record and the applicability of paleontological data to ecology and conservation. Comparisons of living communities to sympatric death assemblages have proved particularly fruitful in assessing biases induced by the fossilization processes and quantifying the expected fidelity of the resulting fossil record. Here we present the results of multi-year sampling via dredging at 52 localities in Onslow Bay (North Carolina, USA). Localities included a wide range of depths and habitats and sampling targeted all macroscopic benthic organisms (both live and dead) obtainable by dredging, including multiple higher taxa with variable skeletal types. Species richness and relative abundance for live and sympatric death assemblages were examined, within and across higher taxa, and relative fossilization potential was estimated for each major taxonomic group.
Results/Conclusions
Samples included 12,981 live and 58,548 dead individuals, 247 species, and 7 phyla (arthropods, annelids, brachiopods, cnidarians, echinoids, mollusks, and sponges). Mollusks and other biomineralized taxa were, not surprisingly, overrepresented in death assemblages. Conversely, groups dominated by organisms with soft-parts or weakly biomineralized skeletons (e.g., arthropods) were typically scarce in death assemblages. Richness and abundance differed predictably when comparing live and dead samples. Namely, higher abundance, higher richness, and greater representation of rare species were observed in death assemblages. The live-dead differences in quantitative measures of community structure that were reported in multiple previous studies were also observed here. That is, we observed depressed Beta diversity and elevated alpha and evenness in death assemblages relative to sympatric living communities. However, overall live community structure was retained in death assemblages, particularly at higher taxonomic levels. The overall live-dead agreement was high (Mantel test r=0.41, p=0.001, 999 permutations). However, compositional similarity within individual phyla and classes was low, with the exception of mollusks (Spearman Rank Correlation, p<0.01). Mollusks outperformed other taxonomic groups, providing more reliable measures of community structure, and could be used to characterize spatio-temporal patterns representative of entire communities. These results support the emerging consensus that the youngest fossil record provides meaningful quantitative ecological estimates, including the spatial structuring of local communities.