Scales of coastal heterogeneity and benthic intertidal species richness, diversity and abundance

Species richness, diversity, total biomass of the benthic macrofauna and macroflora and the biomass of the 2 dominant taxa (Fucus spp and M y t ~l u s eduhs) were examined in relation to coastal heterogeneity at different scales in the intertidal zone The sampling design included randomness at all scales and replication of treatments A 103 km portion of the south shore of the St Lawrence Estuary, Canada, was divided into 1 km stretches of shore (stations)-the large scale-which were classified using a shore heterogeneity index (SHI) into 3 categories (low, medium and high) Species nchness was qualitatively evaluated for each station and substratum heterogeneity on a 100 m (medium scale) was measured as covariate At the smallest scale 4 types of surface (smooth, crevices of 1, 10 and 20 cm) were quantitatively sampled Species nchness tended to increase with SHI category but this tendency was not statistically s~gnificant A multiple regression analysis was carned out to f ~n d which scale of heterogeneity was the most significant for defining species richness Diversity in types of surface did not vary significantly among SHI categones Our results show that large-scale heterogeneity explained a higher proportion of the vanance in species nchness than substratum heterogeneity on a 100 m scale No statistically significant difference was found in total biomass M edulrs and Fucus spp biomass or percent cover among the SHI categones At the small scale (types of surface), the abundance increased significantly from smooth surfaces to 20 cm crevices except for mussels, where abundance was higher in 10 cm crevices The types of surface explained 42% of the variation in total biomass and 21 % of that in Fucus spp biomass Variation in percent cover was explained by the types of surface (40%) a n d to a lesser extent by the SHI (? %) The present study showed that the scales which influenced abundance were smaller than 20 cm in the intertidal zone Thus our results indicated that 2 distinct spatial scales explained the vanab~lity within the same marine intertidal community, i e vanability in species nchness (scale o! 1 km) and in abundance (types of surface, scale of 520 cm)