Feeding biology of a predatory and a facultatively predatory nematode (Enoploides longispiculosus and Adoncholaimus fuscus)

This paper reports on the feeding biology of a predatory and of a facultati vely predatory nematode, Enoploides longispiculosus and Adoncholaimus fuscu s, respectively. Both species represent genera which are common and abundan t in the littoral of the North Sea and in adjacent estuaries. Observations on the foraging behaviour of both species are given, and for the former spe cies, a range of prey from its natural habitat is identified. Respiration w as determined using a polarographic oxygen electrode technique and compared to consumption determined as predation rates on the monhysterid nematode D iplolaimelloides meyli. The daily C-loss due to respiration accounted for 1 5% of the measured C-consumption in E. longispiculosus and for 111% in A. f uscus, proving the observed feeding rates in the latter species to have bee n inadequate for the maintenance of its aerobic metabolism. Daily respirati on rates at an average environmental temperature were 219 ng C ind(-1) d(-1 ) for adults of A. fuscus and 21.9 ng C ind(-1) d(-1) for adults of E. long ispiculosus. Using radiotracer techniques, no uptake of bacterial cells or of organic matter in the dissolved phase was demonstrated for E. longispicu losus. Tn A. fuscus, however, a significant drinking of label in the dissol ved or volatile fraction occurred; bacterial cells were taken up at a level insignificant to the nematode's daily C-ration. It is concluded that E. lo ngispiculosus has a fairly strict predatory feeding strategy, while A. fusc us gains a majority of C from additional foraging strategies, among which t he uptake of dissolved material and scavenging on macrofauna carcasses (as reported in the literature) may be of particular importance.