The Respiratory Physiology of the Marine Nematodes Enoplus Brevis (bastian) and E. Communis (bastian) I. the Influence of Oxygen Tension and Body Size

Rogers (1962) has stressed that the major factors influencing the nematode's ability to obtain oxygen by diffusion are the environmental oxygen tension and its body size especially its body radius. Both he and von Brand (1966, 1968) suggest that the smaller intestinal parasites, such as Nippostrongylus brasiUensis (= muris), maintain an aerobic metabolism, but that larger nematodes like Ascaris lumbricoides lead predominantly anaerobic lives. Saz (1969) considers that stages of certain nematodes, including adult A. lumbricoides have no oxygen requirement for normal production of energy. In contrast, Smith (1969 a, b) raises some fundamental objections to the concept of a unique parasite metabolism. He considers that A. lumbricoides may rely on oxygen derived from intermittent contact with the mucosa to raise the level of aerobic metabolism possible within the gut lumen. Less is known of the oxygen requirements of plant-parasitic or free-living nematodes. Some marine forms have been reported to inhabit muds apparently devoid of oxygen (Moore, 1931; Wieser & Kanwisher, 1961), but the concentration of this gas in the environment does influence the life processes of most plant-parasitic and freeliving forms investigated. Low-oxygen concentrations reduce the rate of emergence of larvae from the cysts of Heterodera schachtii (Wallace, 1956) and from the eggs of Meloidoygne species (Collis-George & Wallace, 1968; Wallace, 1968). The mobility of M. incognita larvae is also dependent upon oxygen concentration (Baxter & Blake, 1969). Cooper, van Gundy & Stolzy (1970) have shown that an occasional reduction in the ambient oxygen concentration lowered the rate of reproduction of Aphelenchus avenae and Caenorhabditis spp. in cultures, and HemicycHophora on tomato plants; the aeration of soils is not constant and may, at times, be greatly reduced (Wallace, 1964). Bair (1955) demonstrated that the onset of a fall in respiration with decreasing oxygen tension occurred at higher oxygen tensions for the soil nematode Rhabditis elegans than for the facultative akin parasite R. strongyloides from a lower environmental oxygen regime. This work considers the influence of oxygen tension on oxygen consumption of two species of marine nematodes from different habitats. Enophis brevis occurs in an estuarine mud within the depth of oxygen penetration (Atkinson, 1972); E. commums