OBSERVATIONS ON THE FEEDING ECOLOGY OF ESTUARINE NEMATODES

Observations on living estuarine nematodes show that previous feeding type classifications do not accurately represent the trophic structure of an intertidal mudflat in the Westerschelde Estuary (Netherlands). A new scheme with six major nematode feeding guilds is proposed: (1) m icrovores; (2) ciliate feeders; and (3) deposit feeders sensu stricto are all nematodes without a distinct buccal armature. In the first two groups bacteria and protozoa, respectively are the major particulate food sources, while other items are included in the diet of the third. The three other categories are recognized among the nematodes with a buccal armature: (4) epigrowth feeders; (5) facultative predators; and (6) predators. Diatoms and other microalgae are an important particul ate food for many epigrowth feeders. The importance of bacteria as a f ood source for these nematodes remains poorly documented. A strictly o r mainly predatory behaviour has been described for only few species f rom the study area. Several nematodes, however, are facultative predat ors. The predatory strategy of Calyptronema maxweberi, as described in this paper, suggests the use of a paralysing or lethal secretion in p rey capture, which, to our knowledge, is the first report for aquatic nematodes. Furthermore, the importance of sources other than particula te food in free-living aquatic nematodes is stressed. Our observations show that many aquatic nematodes are in fact opportunistic feeders, w hich may change feeding strategies in response to available food.