Temperature, Salinity and Plankton in the Eastern North Atlantic and Coastal Waters of Britain, 1957. IV. The Species' Relationship to the Water Body; Its Role in Distribution and in Selecting and Using Indicator Species

Abstract

Temperature and salinity have been used to characterize the surface water bodies of the oceanic eastern North Atlantic and coastal waters of Britain. Species of plankton have been entered on temperature-salinity diagrams and it has been demonstrated that each is related in a characteristic manner to one or more of the water bodies, or their extended influences in mixtures. This relationship is maintained by each species regardless of seasonal temperature fluctuations of the water bodies, and within the available salinity variations. Species may be present concurrently in oceanic water of one temperature and oceanic-coastal water of a different, lower temperature. Increases and decreases in numbers of a species occur within the limits of these water bodies. These factors are regarded as demonstrating, for the area investigated, that species' occurrences and distributions may not be dependent on temperature and salinity.Discontinuities occur in the distribution of species, chiefly at boundary zones between different water bodies. These arise because some species may cross the boundary zone into another water, while other species of similar origin do not (or cannot).An hypothesis is proposed to explain these features. Unspecified properties are postulated for those water bodies which are contributing to mixed waters in the area studied. The relationships of the species are regarded as being regulated by their tolerances towards the properties; and occurrences and distributions of the species are discussed relative to the presence of the properties. It is considered that the species' reactions to the properties provide a reasonable basis on which to explain the relationships to the waters in the area, their apparent independence of seasonal temperature changes, and the species' distribution.