Differential effects of various types of disturbances on the structure of nematode assemblages: an experimental approach

The objective of this study was to test the hypotheses that (1) assemblages of the same broad group of animals respond in a differential way to differ ent classes of disturbance (i.e. there is not simply a generalised stress r esponse), and that (2) the nature of the response differs according to the environmental conditions that the assemblages normally experience. A series of microcosm experiments was carried out to evaluate the responses of inte rtidal nematode assemblages to treatments of physical and biological distur bance and organic enrichment. Assemblages from an exposed sandy estuary poo r in organic matter and from a sheltered muddy estuary rich in organic matt er were compared. Results from univariate, graphical/distributional and mul tivariate methods of data evaluation generally support our initial hypothes is that nematode assemblages exhibit various characteristic changes when ex posed to different types of disturbances. Changes in assemblage structure w ere revealed depending on the type of disturbance, the initial structure of the assemblage and the morphological and physiological adaptations of the species. For both assemblages, biological disturbance caused the least seve re changes in assemblage structure. For the sand nematodes, most extreme ch anges were the result of organic enrichment, while mud nematodes showed the most intense response to treatments of physical disturbance. Assemblages a re most affected by the kinds of disturbances that they do not normally exp erience naturally.