Spatial variation in the composition of motile macroinvertebrate assemblages associated with two bed types of the seagrass Posidonia oceanica

Abstract

The influence of continuous (non-fragmented) and reticulate (fragmented) bed type and plant architecture on the species richness, abundance and assemblage composition of motile macroinvertebrates associated with the seagrass Posidonia oceanica was investigated at 3 different spatial scales (10s of metres [‘small’], 100s of metres [‘medium’] and kilometres [‘large’]). Univariate and multivariate analyses did not identify significant differences in the attributes of macroinverte- brate assemblages between the 2 P. oceanica bed types over the 3 spatial scales considered. On the other hand, significant spatial variation in macroinvertebrate attributes was detected at the large spa- tial scale. Results of univariate regression and multivariate correlation analysis consistently indicated significant relationships between attributes of the macroinvertebrate assemblages and epiphyte bio- mass at the large spatial scale. Although less consistent, significant relationships were also detected between attributes of the macroinvertebrate assemblages, and mean sediment grain size, total organic carbon in sediment and shoot biomass at the large and medium spatial scales. The findings indicate that naturally fragmented and non-fragmented P. oceanica beds have similar habitat charac- teristics for the associated macroinvertebrates and that local factors, which influence seagrass bed architecture and particularly epiphyte load, have greater influence on the seagrass fauna. Data from the present study support the notion that fragmented seagrass beds should receive the same attention as non-fragmented ones with regard to habitat conservation and protection.