The ecologry of anchihaline caves

The dark, mostly brackish, aquatic habitats along the coasts are inhabited by a number of phylogenetically and/or biogeographically interesting animal taxa, whose ecology is poorly known. We are especially ignorant about the nature of the deoxygenated strata that occur in most of these habitats. Are these strata anoxic or only dysoxic? And how are their inhabitants adapted to low oxygen tensions?