Systematics, ecology and feeding biology of estuarine nematodes

L.A. Bouwman

Research output: Thesisexternal PhD, WU

Abstract

As part of extensive biological and chemical investigations in the Ems estuary, the nematode fauna of this area (mainly located in the sediments of tidal flats) was studied.<br/>First, a new method of isolating nematodes was developed, as none of the existing methods appeared to be quantitatively reliable for the isolation of organisms from silty sediments. The new method is based on differences in specific weight between nematodes (and other meiobenthos),and sediment particles: sediment samples are suspended in Ludox-TM, a colloidal silica, and, whereas organisms float to the surface of this suspension, sediment particles sink to the bottom. The isolation method can be used for either preserved or fresh sediment samples.<br/>In a survey of the estuary 121 nematode species were identified and during subsequent investigations 12 other species were noticed: thus, in all 133 species were identified, 4 of which were new to science. The distribution of species over the estuary was studied and the genesis of species associations was related to environmental conditions. Two main faunas were distinguished: one in the Wadden Sea part of the estuary, the other in the Dollart, both extending into the middle reaches of the estuary. In the lower sediment layers a characteristic nematode fauna was found that consisted of species that were mainly absent from the upper sediment layers It was concluded that faunal associations from the lower sediment layers originate from marine subtidal locations, whereas the associations from the upper sediment layers of tidal flats are specific to estuarine tidal environments.<br/>Several nematode species were cultured in agar in the laboratory and their feeding-biology was studied. From these investigations it appeared that nematodes, specific to the surface of littoral macrophytes 3 use non-selective feeding methods, consuming large amounts of bacteria, and, when their buccal cavity is large enough, also diatoms and other algae; the food organisms are ingested by means of continuous oesophageal pulsations. The interstitial nematodes, on the other hand, probably all feed selectively, oesophageal pulsations only being triggered off when a useful food organism is sensed among an overwhelming majority of similarly sized inedible particles. The larger food organisms, diatoms and other algae, protozoa, and small metazoans (including prey-nematodes) may be ingested whole or punctured and subsequently sucked out; specific buccal structures determine which consumption technique is used: when armature is absent food items are ingested whole, when armature is present food items are attacked and sucked out. Individual bacteria are probably too small for most interstitial nematodes and consequently are ignored as food.<br/>Special attention was focused on the ecosystem of the tidal flats close to the outfall in the southeast Dollart. It appeared that in that area the benthic ecosystem was dominated by a herbivorous food-chain, comprising diatoms and diatomconsuming nematodes (throughout the year) and oligochaetes (only in the warmer part of the year).<br/>It is concluded that the success of nematodes in colonizing almost all estuarine biotopes is due to their size, their sophisticated methods of food acquisition and their tolerance of environmental stress. The discharge of organic waste enhances the effects of natural gradients occurring in the estuary. The main effect is the overall decrease of species diversity and the indirect promotion of a herbivorous foodchain in which nematodes predominate the grazing fauna.<p/>
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • den Hartog, C., Promotor, External person
  • Wieser, W., Co-promotor, External person
Award date9 Dec 1983
Place of PublicationWageningen
Publisher
Publication statusPublished - 1983

Keywords

  • aquatic environment
  • benthos
  • estuaries
  • marine environment
  • nematoda
  • eems-dollard

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