Benthic quality assessment using M-AMBI in the Seto Inland Sea, Japan

Benthic invertebrates that inhabit the seafloor respond to anthropogenic and natural stresses, and are good indicators for assessing the benthic ecological status. We evaluated the ecosystem health of the Seto Inland Sea based on the multivariate AZTI Marine Biotic Index (M-AMBI), being its first application in a Japanese coastal sea with numerous endemic species. From the 415 locations studied, we were able to use M-AMBI in 384 sites (92.5% in all sites). The result revealed a statistically significant correlation among biotic indices including AMBI, M-AMBI, Richness, and H’ (p < 0.01). Most of the physico-chemical parameters of the sediment (water content, total organic carbon (TOC) content, sulfide content, mud content, and oxidation–reduction potential (ORP)) were significantly correlated with each other excluding sediment temperature. The M-AMBI was significantly correlated with physico-chemical variables including water content, TOC content, sulfide content, and ORP. We found that the sites classified into the organically enriched cluster, and having high contents of TOC, mud, and sulfide and negative ORP, corresponded with sites that had significantly low M-AMBI values (bad-poor ecological status). Conversely, sites in the unpolluted sandy cluster were assigned high M-AMBI values (high-good ecological status). Therefore, M-AMBI would be a useful biotic index in Japanese coasts due to the representation of the comprehensive sediment quality.