These low energy, muddy ocean shelf ecosystems are moderately productive and typically dominated by microalgal and bacterial primary producers, microbial decomposers, and larger deposit feeders like burrowing polychaete worms and molluscs. Unlike subtidal sand beds (M1.7), the microbial community has a strong influence on biogeochemical cycles. Low oxygen zones can form where concentrations of organic matter and associated high bacterial activity deplete this limited resource.