Tackling the Sulfide Gradient: A Novel Strategy Involving Marine Nematodes and Chemoautotrophic Ectosymbionts

Abstract

Abstract. The Stilbonemutinue (marine free‐living nematodes) arc remarkable for cctosymbiotic bacteria, which cover the greatest part of their body in a highly ordered and species specific pattern. Using SEM we describe the main types of symbiotic cover and give evidence for the role of the bacteria in the nutrition of their host on the basis of stable carbon isotope ratios. In experimental systems the worms migrated repeatedly across a sulfide gradient during 12 h when sulfide concentrations were low, but stayed above the sulfide maximum at high concentrations. The migration across the chemocline exposes the symbionts alternately to reduced sulfur compounds and oxygen; this constitutes an alternative strategy to the ventilation/circulation systems in symbiotic macrofauna from sulfidic habitats.

Leptonemella species (Desmodoridae, Stilbonematinae), benthic marine nematodes with ectosymbiotic bacteria, from littoral sand of the North Sea island of Sylt: taxonomy and ecological aspects

“…Arguments in favor of the hypothesis are given by pointing to the similarities between intestinal and ectosymbiontic microbes (e.g. Jensen 1987b) and to stages of lysis in the intestine (Ott and Novak 1989;Ott et al 1991). Jensen et al (1992) consider that digestion occurs in the posterior part of the gut.…”

“…According to observations on the vertical distribution of Caribbean Stilbonematinae (Laxus oneistus; Ott et al 1995) in laboratory experiments, these nematodes expose their symbionts alternately to reducing or oxidizing conditions by migrations through the chemocline in both directions (Ott et al 1991). Another strategy for providing sulfide oxidizing ectosymbionts with suitable environmental conditions has been suggested by Ott et al (1998) and modified by Vopel et al (2001) for a sedentary, feather-shaped, colonial peritrich ciliate that expands into oxygenated water and contracts into sulfidic water close to the substrate.…”

“…In laboratory experiments, individuals of Leptonemella revealed a high tolerance of hypoxia and high sulfide concentration. Preference tests (methods according to Ott et al 1991) showed the preference of Leptonemella species for the chemocline in the oxygen/sulfide gradient system (Bock 1999).…”

“…About 30 species of these nematodes have been described from many places around the world. They live in sheltered intertidal and subtidal sulfidic sediments, mainly at the interface between the oxidized surface layer and the deeper, anoxic sediment (Ott and Novak 1989;Ott et al 1991). The symbiotic, uniform bacteria which colonize the surface of the worms in various characteristic patterns are chemoautotrophic oxidizers of sulfide and other reduced sulfur compounds (Schiemer et al 1990;Polz et al 1992Polz et al , 1994Hentschel et al 1999).…”

Black spots produced by buried macroalgae in intertidal sandy sediments of the Wadden Sea: Effects on the meiobenthos

“…Rosenberg et aL, (1991) observed that infaunal animals moved away in search of oxygen or to escape from hydrogen sulphide. The ecological potential of habitats exposed to sulphide can only be utilized by those organisms that are physiologically adapted to such hostile conditions which means that they cannot only cope with exposition to lasting hypoxia or even anoxia, but also with exposition to toxic and highly permeable hydrogen sulphide (Powell, 1989;Ott et aL, 1991). In organically enriched (but not overloaded) sediments, biological activities of infauna can promote the decomposition of organic matter and the oxidation of sulphides (Chareonpanish et aL, 1993).…”