Original paper

Tolerance of two tubificid species (Tubifex tubifex and Limnodrilus hoffmeisteri) to hypoxic and sulfidic conditions in novel, long-term experiments

Volpers, Markus; Neumann, Dietrich

Abstract

Tubificid assemblages (seven species) from two eutrophic gravel-pit lakes (depth about 16 m) were studied in relation to hydrographic conditions (seasonal profiles of temperature, O2, pH, conductivity). In both lakes, severe hypoxia from June to November was accompanied by sulfide concentrations of up to 25 μmol L-1 (0.85 mg L-1) in the hypolimnion. While the absolute abundance of all tubificids decreased during this stagnation period, the relative abundance of Tubifex tubifex increased consistently because the other tubificid species, such as Limnodrilus hoffmeisteri, suffered particularly high mortality.In long-term laboratory experiments of up to 14 weeks at 10 °C, groups of T. tubifex and L. hoffmeisteri (eight to ten 4 mg-specimens each) were kept under various severely hypoxic and sulfidic conditions in a newly developed, computerised flow-through system simulating profundal conditions. The tubificids were able to remain in an almost natural substratum during the experiments.In T. tubifex, the defecation rate (which is correlated with metabolic rate) was always slightly higher than that of L. hoffmeisteri. It was independent of oxygen content down to 0.5 mg O2 L-1, but stopped below 0.3 mg O2 L-1.L. hoffmeisteri was much more sensitive to a sulfide concentration of about 30 μmol L-1 in hypoxic medium (0.5 mg O2 L-1, corresponding to 0.93 % PO2) than T. tubifex was. Under these conditions, Tubifex tubifex showed much lower mortality and even better growth than L. hoffmeisteri did.The higher sulfide tolerance of T. tubifex in hypoxic conditions correlates with the dominance of this tubificid in the profundal of eutrophic lakes. This also relates to the higher sulfide resistance of both respiration rate and anaerobic energy metabolism in T. tubifex.

Keywords

tubifex tubifexlimnodrilus hoffmeisterisulfide toleranceo2-deficiency tolerancedefecation rateprofundal simulator