Feeding biology of the brackish-water oncholaimid nematode Adoncholaimus thalassophygas

Abstract

The brackish-water inhabiting nematode Adoncholaimus thalassophygas (De Man, 1876) may be classified as an omnivore and predator according to the gut contents of the adults. A series of ¹⁴C experiments was conducted to investigate the feeding potential of labelled microorganisms and dissolved ¹⁴C glucose. The observed consistent failure to incorporate ¹⁴C from labelled microorganisms, and its consistent success with dissolved ¹⁴C glucose suggests that dissolved organic matter may be more important than microorganisms as a food source for his nematode. This corresponds also with direct observations of living worms which showed very little uptake of particulate food other than that originating from predation. Defecation and mean gulping rates were low and, therefore, ¹⁴C glucose uptake from solution can hardly be explained by the assumption that large amounts of water are swallowed and passing through the gut. By means of mucus secretion, A. thalassophygas forms compact agglutinations of detrital sediment which are sites of enhanced microbial activity. We suggest that hatched juveniles feed primarily on dissolved organic matter released by the intensive microbial activity within this habitat. Adults retain the ability to utilize dissolved organic matter, and supplement their diet by scavenging on carcasses and occasional predation. Thus, the biology of oncholaimid nematodes may be characterized by an intimate linkage to microbial metabolism, although they do not appear to feed directly upon microorganisms.