Evaluation of spatial and temporal variability of multiple measures of diversity in three intertidal assemblages

Abstract

Estimates of biodiversity in species assemblages are important in prioritizing conservation efforts, especially in urbanized habitats. Many indices have been developed to measure different aspects of biodiversity. The most commonly used, species richness (SR), is measured directly or estimated from samples. Species density (SD), or the mean number of species per sample, also describes species richness, although the 2 indices measure different aspects of diversity. The proportions of rare and common species and the heterogeneity of an assemblage measure different components of biodiversity. Few studies have examined spatial and temporal patterns of diversity for multiple measures of diversity for different assemblages living in the same patches of habitat. Here, SR, SD, the percentages of rare and common taxa, spatial heterogeneity of assemblages within sites and site-endemism were compared among 3 assemblages living on intertidal boulders in summer and winter for 2 years at 6 sites. The assemblages were algae, mainly found on the tops of boulders, sessile animals, mainly found on the undersurfaces of boulders, and mobile animals, which move between surfaces and among boulders. Temporal and spatial patterns varied inconsistently among all measures for the different assemblages, although most temporal changes were common among sites. Importantly, algae, sessile animals and mobile animals, which may be considered to constitute a single intertidal-boulder assemblage, showed different spatial and temporal patterns for all indices. Thus, when making decisions about protecting or managing biodiversity, it is important to examine not only multiple indices that relate to diversity, but also different components of an assemblage.