Meiobenthic assemblages as ecological indicator of natural variability induced by ecosystem engineers

Indonesia is biologically one of the most diverse areas in the world. Nevertheless, its biodiversity is underestimated, and this is particularly evident for meiobenthic assemblages. Seagrass meadows are known to be ecosystem engineers that can significantly modify the habitat heterogeneity and, thereby, increase the meiobenthic diversity. Therefore, a study on the meiobenthic distribution and biodiversity was conducted in two seagrass meadows around Siladen Island (Bunaken Marine National Park): Barat and Lagoon, characterized by different sedimentary regimes, as well as by different anthropogenic impact. An overall high level of diversity indices and richness were recorded (H′: 1.19–1.69; J: 0.46– 0.67; number of taxa: 9–14), with meiobenthic abundances ranging between 770 and 2529 ind. 10 cm−2. The lowest meiobenthic abundance and diversity (i.e. Shannon-diversity, number of taxa) were reported at Barat meadow, probably in response to sedimentological modifications and higher anthropogenic pressure at this site. Differences in meiobenthic assemblage structures were particularly evident when only rare taxa were considered (i.e taxa found in low abundances and characterized by a sporadic distribution in the study area). This result underlines the role of rare species as possible indicators of spatial variability generated by engineer species and different environmental conditions.