Distribution of soft bottom macrobenthic communities in tropical marinas of Singapore

The establishment of marinas alters physico-chemical conditions and affects distribution of resident epibiotic and pelagic communities along coastal areas. However, information on the soft bottom macrobenthos within and around these boating facilities in the tropics is limited. Here, we investigated if macrobenthic communities differed among three representative tropical marinas, and whether the communities inhabiting the marinas differed from those outside the marinas. Ekman grab sampling of the soft bottom sediment at three Singapore marinas – Raffles Marina (RM), ONE^o15 Marina (OMC), Marina at Keppel Bay (MKB) – yielded a total of 73 taxa from eight phyla. Accounting for temporal variations, taxonomic richness did not differ among marinas, while Shannon index (MKB > RM = OMC) and abundance (RM > OMC > MKB) did. Macrobenthic community composition differed among the marinas, with RM dominated by a high proportion of opportunistic species and OMC supporting species that were sensitive to pollution. The surveys also revealed that communities within and outside marinas differed. Unlike RM which is more enclosed, diversity was higher within MKB than outside it, likely because the latter marina had a layout that encouraged flushing which maintained good water quality. The study showed that while Singapore’s tropical marinas can support diverse groups of macrobenthic taxa, the presence of high proportions of opportunistic species suggested that pollution within the marinas was still significant. Macrofaunal diversity in tropical marinas, such as those in Singapore, may be promoted by designs that improve water exchange.