Ecology and cultivation of the herbivorous brackish-water nematode Eudiplogaster pararmatus

The sediment inhabiting rhabditld nematode Eudiplogaster pararmatus (W. Schneider 1938), is a halophilic member of the family Dlplogasteridae (non-marine animals, often occurring in saprobic environments). It colonizes successfully the waste-water exposed intertidal mud flats in the southeast of the Ems-Dollard estuary, The Netherlands. Microscopic observations in agar cultures witness that E. pararmatus feeds on diatoms. The nematode consumed representatives of 7 different diatom species by puncturing their frustules and swallowing their contents. Adults consumed about 7 cells h-' of Navicula saljnarum (Grunow). Comparable consumption rates were calculated from experiments by other researchers, with 14C labelled diatoms. The reproduction and population growth of E. pararmatus were studied in cultures with various salinities and diatom densities at a temperature of 17 'C. Reproduction occurred under almost all conditions but the number of nematodes increased importantly only in cultures with low salinities (0.5 to 2.5 460 S) and food densities of over 2 X 106 cells cm-3. Growth of individual nematodes was studied at 2 different temperatures in agar cultures with low salinities and adequate food. Temperature appeared to govern the moment of sexual differentiation: at 12 "C, this differentiation occurred after approximately 2.5 wk; at 21 "C, after only 1.5 wk. Generation times observed in cultures varied between 45 d (at 12 "C) and 21 d (at 21 'C); this is in the same range as the generation time found for other brackish water and marine nematodes with a similar life style Tentative calculations of the reproductive rate of exponentially growing populations in the field (in spring, 12" to 18 'C), revealed a generation time of 25 to 33 d; this is slightly shorter than the generation time observed in cultures. Brief exposure to high temperatures during emersion of the flats may be responsible for this difference