Morphological and Ecophysiological Adaptations of the Marine OligochaeteTubificoides benediito Sulfidic Sediments

Abstract

SYNOPSIS. The marine oligochaete worm Tubificoides benedii inhabits coastal tidal sediments in which sulfide can reach toxic concentrations. The role of external ironsulfide deposition in sulfide detoxification is discussed together with a review of morphological and ecophysiological adaptations of T. benedii to sulfide. The body wall of T. benedii turns black in the presence of sulfide. Histochemical studies and micro-X-rayanalyses provide evidence for the reaction of iron in the mucus layer above the cuticle of the worm with environmental sulfide to produce ironsulfide. The deposited ironsulfides are either reoxidized or shed off through moulting, a process otherwise unknown in oligochaetes. However, calculations on the diffusion rate of sulfide into T. benedii show that the deposition of ironsulfides do not play an important role in sulfide detoxification. The first and last few segments of T. benedii are not blackened by sulfide and do not appear to precipitate sulfide. The diffusion rate of sulfide through these segments is so rapid that internal sulfide concentrations reach levels inhibitory to cytochrome c oxidase, the key enzyme of aerobic respiration, within minutes. When internal sulfide concentrations increase to toxic levels, reliance on an anaerobic metabolism represents a successful mechanism of sulfide tolerance in T. benedii. Metabolic adaptations to hypoxia and sulfide include the maintenance of aerobic pathways despite low oxygen or high sulfide concentrations and the ability to gain energy through anaerobic pathways when oxygen and/or sulfide concentrations become limiting