The region of the eastern North Pacific coastline dominated by the California Current was surveyed annually from [2001][2002][2003] to examine (1) benthic macro-invertebrate and algal populations, (2) the magnitude and patterns of key environmental variables, and (3) how dynamic populations and communities of macroalgae and invertebrates respond to spatial differences in nearshore geomorphology, wave dynamics, and oceanography of the coastal shelf. We used a highly replicated spatially nested sampling design consisting of 144 shore segments (bedrock platforms longer than 50 m) with three replicate segments per site (,1 km), three sites per area (,10 km), and sixteen areas (.10 km) grouped into six domains (hundreds of kilometers). Results suggest that (1) low zone diversity was higher at northern latitudes when measured at segment, site, and area scales, but at domain scales there were more species at southern latitudes; (2) community structure showed high fidelity to geographic location with community similarity inversely related to separation distance, and the only regional scale biological discontinuity in community structure was centered near Pt. Conception; and (3) wave runup was the most significant physical parameter affecting overall community structure, however, tidal range, precipitation, air and water temperature, upwelling, salinity, and sand were significant mechanisms forcing differences in community structure within the region.Understanding the underlying causes of gradients of diversity has been a long-standing focus of the ecological community. The problem is complex and has been beset by controversy, yet great strides have been made (Huston 1995;Rosenzweig 1995;Hubbell 2001). A recent focus has been on the relative contributions of local factors, dispersal, and scale-dependent regional factors that influence regional species pools (Ricklefs 2004;Witman et al. 2004;Russell et al. 2006). The increased focus on largescale dynamics, however, has exposed a major shortcoming in many of the datasets that have been used to evaluate diversity hypotheses: the level of detail and resolution is

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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 familylevel 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.

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