An ecophysiological approach to the microdistribution of meiobenthic Oligochaeta, II : Phallodrillus monospermathecus (Tubificidae) from boreal brackish-water shores in comparison to populations from subtropical beaches

Abstract

Phallodrilus monospermathecus, a typical interstitial oligochaete from Baltic and North Sea beaches, shows a characteristic microdistribution preferring the moist layers usually slightly above ground water which are sufficiently supplied with water and oxygen, protected against wave action and devoid of hydrogen sulfide. - Ecophysiological experiments testing the resistance against temperature, salinity, alcalinity, and hypoxia proved the populations to be extremely euryecous tolerating single factors far beyond their natural range. However, combinations of adverse factors reduced the tolerable limits, especially those of salinity, considerably. - In boreal climate, the habitat fluctuations for many physiographical factors apparently lie well within the tolerable range of the populations. Hence, the distributional pattern of Ph. monospermathecus from Baltic and North Sea beaches must be ascribed mainly to long-term and preference reactions and probably also to biotic factors (food supply, competition), and is less definable by short-term tolerances. This is in contrast to conspecific populations from Bermuda beaches. Here, the subtropical climate shifts the maximal oscillations of physiographical parameters close to the tolerance limits which makes the field distribution of the population explicable already by short-term survival tests (GIERE, 1977a). - Considering the differing distributional limits of Ph. monospermathecus in their climatically diverse habitats, the nature ot ecophysiological adaptation in this ubiquitous meiobenthic species is discussed