These lightless slopes of sand, mud and rocky outrops run down from the shallower shelf break to the very deep abyssal basins. Nutrients falling from upper ocean layers and delivered by currents from the shelf support diverse communities of microbial decomposers, detritivores like crabs and demersal fish, and their predators, but sessile animals are rare and algae are absent. Biomass is relatively low and peaks at mid-slope, diminishing with depth as food and temperature decrease and bathymetric pressure increases.