The Distribution of Free-Living Nematodes in Relation to Salinity in the Middle and Upper Reaches of the River Blyth Estuary

Abstract

The habitat of mud-dwelling estuarine nematodes consists essentially of an extremely complex mixture (Baver 1948) of inorganic and organic particles surrounded by interstitial water. Except when the mud dries out completely the body surface of a nematode in this habitat is continually in contact with the interstitial water. Exposure, salinity changes, and other characteristics of estuaries affect nematodes only in so far as they affect conditions in this water. The ecological factors peculiar to this habitat can be seen to be very different from those affecting nematodes living on rocky shores, intertidal seaweeds or marine beaches. The original work on the marine nematodes of this country is that of Bastian (1865). This was followed by a number of recordings and descriptions of new species made by Southern (1914) during the Clare Island survey. Since then the nematodes of the Plymouth area have been described by Schuurmans-Stekhoven (1935b) and by Wieser (1951, 1952) in two important works. In his latest paper Wieser studied the vertical distribution of nematodes inhabiting intertidal seaweeds, and although the detailed ecology of the species found in this habitat cannot be extrapolated to the present investigation, the species recordings and the general intertidal ecology of the nematodes studied have been useful for comparison. Moore (1931) and Mare (1942) have studied nematodes as a group, without distinguishing the species, during wider investigations on marine benthic communities, and Rees (1940) has dealt generally with intertidal nematodes. The work of Rees dealt with the horizontal and vertical distribution of nematodes found during a wider survey of the ecology of a mud flat in the Bristol Channel, but none was identified. His work has been used as the only available point of departure for the present investigation. The distribution of free-living nematodes in water of varying salinity has been the subject of much research in the Baltic and in certain areas of the Zuiderzee. An extensive literature exists for the Belgian coast, the North Sea coast of Germany and the Dutch coast, which is summarized in Schuurmans-Stekhoven (1935a) and more recently by Wieser (1951). In the Zuiderzee and the Baltic, rates of salinity change are much less rapid than those found in estuaries and the distribution of