BIVALVE DEAD-SHELL ASSEMBLAGES ARE STRONG SURROGATES FOR WHOLE BENTHIC MACROINVERTEBRATE COMMUNITIES IN PUGET SOUND

To integrate paleoecological data with the “whole fauna” data used in biological monitoring, analyses usually must focus on the subset of taxa that are inherently preservable (by virtue of biomineralized hardparts) and those skeletal remains must also be identifiable in fragmentary or otherwise imperfect condition (perhaps requiring genus- or family-level identification). However, can shelly death assemblages reflect similar patterns of compositional variation among samples as exhibited by the entire infaunal macroinvertebrate community? We evaluated faunal count data from ten established subtidal stations in Puget Sound, Washington State. Among-sample distance matrices were produced for data based on five taxonomic subsets (the whole fauna, polychaetes, malacostracans, living bivalves, dead bivalves) at four levels of taxonomic resolution (species, genera, families, orders) evaluated under four numerical transformations of the original count data (proportional abundance, square-root and fourth-root proportional abundances, presence-absence), resulting in a total of 80 surrogate matrices. Second-stage ordination was used to plot inter-matrix correlations and determine the strength of surrogates as proxies of the original live-collected whole fauna data. We found that living and dead bivalves had nearly identical potential to serve as surrogates of the whole fauna; they were further offset from the whole fauna than was the polychaete subset (which dominates the whole fauna), but were far superior as surrogates than malacostracans. Genus- and family-level data were consistently strong surrogates of species-level data for most taxonomic subsets, and correlations declined for all subsets with the intensity of data transformation. These strongly positive results in a setting with potential to impose strong taphonomic bias on shell preservation (e.g., strong tides, and dissolution stress from cold bottom waters) are encouraging for use of bivalve dead-shell assemblages as a complement to monitoring data in regions with strong natural environmental gradients.