Respiration rates of free-living marine nematodes in the subtidal coarse-sand habitat of Otsuchi Bay, Northeastern Honshu, Japan

Abstract

Respiration rates of six free-living nematode species dominant in the subtidal coarse-sand habitat of Otsuchi Bay, Northeastern Honshu, Japan, were measured discriminating sex and adult or juvenile. To measure the respiration rate, each nematode was put in a temperature-controlled microchamber of 45 mul in volume, and the dissolved oxygen concentration of the seawater was monitored for more than 3 hrs. Measurements were done at 5, 10, 15, and 20 degreesC, covering the yearly temperature range of the habitat. Metabolic intensities (M.I) of these species at 20 degreesC were within the range of values previously reported for other nematode species. Juveniles of Mesacanthion sp. had the highest M.I. among the species measured, reflecting the carnivorous nature of the species. For Polygastrophora sp., Mesacanthion sp., Metachromadora sp. and Monoposthia sp., M.I. decreased at lower temperature, and the Q(10) value was close to 2. On the other hand, M.I. values of Symplocostoma sp. and Theristus sp. were independent of the change of temperature and the Q(10) value was close to 1. For Symplocostoma sp., Polygastrophora sp. and Mesacanthion sp., M.I. of male was higher than that of female. Males of all these species were rare and may need to be more active than females, to copulate with many females.