Taxonomic sufficiency in distinguishing natural spatial patterns on an estuarine shoreline

Studies of marine benthic communities have shown that pollution impacts can often be detected without identifying taxa to the species level, thus saving considerable time and cost. We tested whether differences among unpolluted intertidal communities along weak estuarine physical gradients could similarly be detected with various species aggregates. We used a spatially hierarchical sampling design to study species-rich, low-shore communities from pebble-sand beaches in Puget Sound, Washington. Previous research showed that: weak north-south gradients in salinity, wave energy, and proportion of fine sediments correlate clearly with species richness of the benthic epibiota and macroinfauna. In this study, we found similar correlations with data aggregated to the family level but weaker correlations at higher levels (class, phylum, or trophic groupings). Multivariate analyses of community data at the species level show distinct separation among geographically distinct areas; similar spatial patterns are visible almost as clearly when data are gathered at lower resolution in the field or when species-level data are aggregated to families. Higher-level aggregations cause spatial patterns to become progressively less distinct. Much of this effectiveness of family-level aggregation stems from the biota being family-rich but with few species per family. For this biota, monitoring programs using only families or other readily identifiable taxa should be able to detect many potential changes in community patterns in space or time. Incorporating occasional surveys using identification and analysis at the species level would add the capacity to examine biodiversity and possible within-family changes in species abundances.