It is common practice to divide hydrobiosphere and hydrosphere into a maritime domain and a continental domain each possessing its own features, its original populations, its sedimentary processes and its distinct geochemical characteristics.
Bordering these two great domains, there exist a number of milieux apparently very different from one another described by an extensive terminology: saltwater lake, lagoon, brackish lagoon, bay (Arcachon), sea marsh, mangrove swamp, salt marsh, polder, estuary, ria, fjord, aba, delta, tidal water splash, coastal sebkha, melaha, etc. These milieux, very rich from an economic point of view, have been and still are the object of many applied studies, either with a view toward their exploitation or their development. For example (Amanieu, 1973), for the year 1971, the production of small-scale fishing alone in the Etangs de Thau and Berre is superior (33 million francs) to the output of the combined French coastal trawlers (30 million francs). Moreover, the value of the conchological production of the Etang de Thau alone (15 million francs) is almost equal so that of the production of the entire sardine fleet (18 million francs).
The generic terms used to qualify these milieux are as imprecise as they are unsatisfactory and show the perplexity of the authors faced with the “mixed” aspect of these milieux and their diversified geochemistry: one can find in literature (biólogical as well as geological) terms such as: transition milieux, mixing zones, intermediary milieux, variable salinity milieux, coastal fringing zones, brackish milieux. Here the the term paralic1 is used, created by Nauman in 1854 to qualify the coal beds in which a certain marine influence can be detected; the term was used by Perthuisot in 1975 to qualify certain evaporitic basins whose salts are essentially of marine origin. In this context, the adjective “paralic” applied to an area, a basin or a milieu simply means that it possesses a certain relationship with the sea.
One can wonder whether the morphological variety and geochemical diversity of paralic milieux found today in nature entail an equivalent diversity in their populations and their biological dynamics.
1 From the Greek “para” near, “halos” salt (and, by extension, the sea)
