Ecocline

An ecocline is a variation of the physicochemical environment dependent of one or two physico-chemical factors of life, and thus presence/absence of certain species. An ecocline can be a thermocline, chemocline (chemical gradient), halocline (salinity gradient) or pycnocline (variations in density of water induced by temperature or salinity).

An ecotone describes a variation in species prevalence and is often not strictly dependent a major physical factor separating an ecosystem from another, with resulting habitat variability. An ecotone is often unobtrusive and harder to measure.

An ecotone is often associated with an ecocline: a "physical transition zone" between two systems. The ecotone and ecocline concepts are sometimes confused: an ecocline can signal an ecotone chemically (ex: pH or salinity gradient), or microclimatically (hydrothermal gradient) between two ecosystems.