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Efficiency in biomonitoring studies is essential to maximize return (i.e. useful data) for investment (e.g. time, training, personnel). Here, we test several options for reducing data resolution when streamlining monitoring protocols, and use the results as a framework to discuss the costs and benefits of decreasing information when sampling intertidal assemblages. Specifically, we ask; (1) Is it necessary to collect species abundance data, or is species presence–absence information sufficient to differentiate sites? (2) Is it necessary to sample organismal abundance at the species-level or is coarser (higher taxon or functional group) resolution sufficient to resolve patterns of difference in intertidal community structure? and (3) How general are these patterns across different oceanic regions? We answer these questions using data from Northeast Atlantic, Northwest Atlantic, Northeast Pacific, and Southwest Pacific intertidal monitoring studies. Results show that compared to species-level sampling, genus-level sampling requires knowledge of 25% fewer taxa, but results in only a 5% difference in the ability to discern between-sample similarities. Likewise, family-level sampling involves 50% fewer taxa, and is accompanied by only an 8% difference in between-sample similarities. Species lists and functional groups were variable in performance, working well for some regions, and poorly for others. These findings will assist in the selection of monitoring protocols with the potential for increased geographic scope and temporal frequency of sampling, resulting in longer time series of data collection, and a reduction in the required taxonomic skills for individuals involved in scientifically useful biomonitoring programs.

Most investigations of biogenic habitat provision consider the promotion of local biodiversity by single species, yet habitat-forming species are often themselves components of diverse assemblages. Increased prevalence of anthropogenic changes to assemblages of habitat-forming species prompts questions about the importance of facilitator biodiversity to associated organisms. We used observational and short-term (30 days) manipulative studies of an intertidal seaweed system to test for the implications of changes in four components of biodiversity (seaweed species richness, functional group richness, species composition, and functional group composition) on associated small mobile invertebrate epifauna. We found that invertebrate epifauna richness and abundance were not influenced by changes in seaweed biodiversity. Invertebrate assemblage structure was in most cases not influenced by changes in seaweed biodiversity; only when algal assemblages were composed of monocultures of species with ‘foliose’ morphologies did we observe a difference in invertebrate assemblage structure. Correlations between algal functional composition and invertebrate assemblage structure were observed, but there was no correlation between algal species composition and invertebrate assemblage structure. These results suggest that changes in seaweed biodiversity are likely to have implications for invertebrate epifauna only under specific scenarios of algal change.