Influence of taxonomic resolution and morphological functional groups in multivariate analyses of macroalgal assemblages

This paper examines how the use of various taxonomic levels and morphological functional groups influences the interpretation of multivariate analyses when comparing macroalgal assemblages in different regions in the Northeast Pacific. We found that for intertidal assemblages, within-site variation was high at the species level and regions only became discernable from the genus level to the order level. Above order level, regions were less well distinguished. Differentiating assemblages at the genus level were similar to results from functional group analyses. This implies that various levels and morphological functional groups can be used to distinguish intertidal assemblages among regions. Intertidal strata differences could be discerned at all taxonomic levels and using functional groups. In contrast to the intertidal, only a few regions were significantly different for subtidal assemblages, independent of taxonomic resolution used. Functional grouping in subtidal assemblages yielded the same resolution as taxonomic levels. Conversely to the intertidal assemblages, strata differences in the subtidal were found at the species and genus levels and with functional groups but not at the family and higher levels. Overall, these results demonstrate differences in regional and strata comparisons in intertidal and subtidal assemblage analyses and that typically species-level analyses are not required.