The conservation of brackish-water systems: priorities for the 21st century

Abstract

There is a marked contrast between the theory and the practice of conservation in terrestrial environmentson the one hand and in most aquatic environments, including those of the coastal marine zone, on theother. It is effectively axiomatic in the terrestrial sphere that conservation requires active management. Itis not sufficient simply to safeguard an area from external threats, although that could also be important.Without active intervention, a given terrestrial system is likely to change into another, almost certainly oflesser conservation interest. The habitat must be manipulated so as to maintain it in a form suitable forthe species and the communities of interest, and the populations of certain species—most especiallyvarious potentially superior competitors and often significant consumers—must be controlled in order tofavour others. Burning, grazing and many other tools are routinely used to prevent natural changes. Toa degree, the same is also true of freshwater habitats: control of water tables, of water quality, of fringingstands of vegetation and of submerged aquatics are all well-known and much practised measures.Marine and brackish-water systems are treated differently, however. Through much of the past, thesehave been conserved only insofar as they lay within the boundaries of conservation areas declared—andmanaged—for other purposes, whether these have been botanical or ornithological. More recently,however, they have become the focus of conservation interest in their own right with the declaration ofMarine Nature Reserves, or Special Areas of Conservation as a consequence of the ‘Habitats Directive’(