Comparisons of Fronts with Terrestrial Boundaries and the “Ecotone” Concept

Marine fronts possess most of the main characteristics of ecotones, as defined for land ecosystems, so fronts can be considered as true ecotones. In addition to land ecotones features, marine fronts are characterized by high biological productivity, a property rarely (if ever) reported for terrestrial ecotones. Moreover, concentration and retention of small planktonic forms in marine fronts plays a much more important ecological role than analogous processes on land. Both high biological production and retention/concentration are responsible for the noteworthy concentration of life at marine fronts. On the other hand, terrestrial landscapes may be modified by human actions, usually increasing contrasts across boundaries (habitat fragmentation); this is another significant difference with marine fronts, which cannot be created by human actions, though they may present significant long-term variability in response to climate change. Fronts and ecotones can represent unique habitats optimal to some species and inhospitable to others; they are places of tension where evolution forces may be at work. The age and history of fronts and ecotones may determine their functional properties, their ecological impacts increasing with their persistence.