An ecological survey of the abundance and diversity of benthic macrofauna in Indonesian multispecific seagrass beds

Seagrasses are one of the most productive ecosystems in coastal areas and support a wide variety of associated fauna. The tropical Indo-Pacific region is considered to have the highest diversity of seagrass plant species and the largest distribution areas of seagrass, yet the seagrass macrofauna in this region are poorly understood. To help fill this gap in our knowledge, an ecological survey was conducted to describe the abundance and diversity of benthic macrofauna from tropical seagrass beds and to determine between-station variations within a transect and between-site variations in macrofaunal abundance, taxa richness and community structure. Benthic macrofaunal samples associated with seagrass beds were collected with a core sampler on the east coast of North Sulawesi in May 2014 and on the west coast in October 2015. A total of 149 species from 14 higher taxa was collected. The most species-rich groups were polychaetes (56 species, 26% of total individual numbers), decapods (20 species, 9% of total numbers) and amphipods (18 species, 35% of total numbers). Between-station variations within a transect displayed different patterns between the east coast and the west coast. On the east coast, there were marked variations in abundance between stations within a transect for the macrofauna and amphipod assemblages. Both taxa richness and abundance varied with station for the macrofauna and polychaete assemblages on the west coast, resulting from the heterogeneity of the substrate along a transect. One-way ANOSIM together with MDS ordination indicated that macrofaunal community structure in seagrasses differed significantly between the east coast and the west coast, corresponding with the division of seagrasses into two broad categories of habitats, i.e., mangrove-seagrass-reef continuum and seagrass-reef continuum. Compared with other studies in tropical areas, the abundance and diversity of benthic macrofauna in the present study were moderate. The reason for the two markedly distinct macrofaunal communities might be attributed to multiple factors, including sediment pattern, seagrass structure and temporal changes.