Laboratory experiments on the infaunal activity of intertidal nematodes

Abstract

The impact of oxygen on the vertical distribution of an intertidal nematode community was investigated in a manipulation experiment with sediments collected from the Oosterschelde (The Netherlands). The vertical distribution of nematodes was examined in response to sediment inversion in perspex cores with or without the presence of an air-flushed silicone tube introducing oxygen to the bottom sediment layer. Following an incubation of 1 week, peak densities of nematodes were recorded in the deep layers of the sediment in cores with subsurface oxygenation. In contrast, this concentration of nematodes was absent in the cores that lacked bottom oxygenation and the majority of the total assemblage was still located in anoxic sediment layers. This suggests that oxidised sediments with traces of oxygen represent favourable conditions for nematodes and indicates that these nematodes are tolerant to short-term anoxia and burial. Observations on the species level suggest that oxygenation, primarily through its direct impact on geochemical properties of the sediment, may be an important factor governing the subsurface activity of nematodes.

Contrasting macrobenthic activities differentially affect nematode density and diversity in a shallow subtidal marine sediment

“…The recorded high nematode density at depth was mainly visible in Sabatieria celtica and to a lesser extent in Microlaimus conothelis and Richtersia inaequalis profiles. Whereas it is generally accepted that S. punctata and S. pulchra are resistant (Jensen 1981, Steyaert et al 2005) to anoxia and associated elevated hydrogen sulphide concentrations, observations on the distribution of S. celtica on the one hand and M. conothelis on the other are less clear: Soetaert et al (1994Soetaert et al ( , 1995 showed a deep and opportunistic distribution of S. celtica, whereas Jensen (1983) and the control treatment in the present study point to a preference for oxygenated layers. Similarly, Heip et al (1985), Wetzel et al (1995) and Steyaert et al (1999) point towards a deep distribution of M. conothelis, whereas the control treatment in the present study showed avoidance of deep layers.…”

“…the low R 2 value in the DISTLM analysis). (1) This may point at missing measurements of important structuring factors such as oxygen penetration depth (Steyaert et al 2005). (2) It may indicate a uniform response of the nematode species to the altered environmental variables, as reflected in the higher correlation with the univariate measures nematode density and diversity.…”

Nematodes as indicators of environmental quality in seagrass (Posidonia oceanica) meadows of the NW Mediterranean Sea

“…Several studies pointed out that small, short and stout Nematodes, which are characterized by higher growth rates and a reduced age at first breeding, act as opportunists in shallow and ocean-margin areas [85][86][87]. Nematodes of MPA meadows showed a more heterogeneous community with a comparatively broader range of the most abundant genera and resulted characterized by the presence of sensitive genera, such as Richtersia, Halalaimus and Bolbolaimus [e.g., 32,54,88,89] in both periods, indicating good environmental quality. The nematode assemblages were likely to be related with organic enrichment associated to sewage discharge, which resulted as the main factor explaining their variability.…”

An experimental protocol to select nematode species from an entire community using progressive sedimentary enrichment

“…Only the contributions of species to ∼50% of the overall dissimilarity between the treatment groups are given. R R R R T1A T1A T1A T1A T2A T2A T2A T2A T3A T3A T3A T3A T1A RAc RB RBc T2A T1Ac T1B T1Bc T3A T2Ac T2B T2Bc T4A T3Ac T3B T3Bc ANOSIM ( Faunistic comparisons T4A T4A T4A T4A T5A T5A T5A T5A T6A T6A T6A T6A T7A T7A T7A T7A T5A T4Ac T4B T4Bc T6A T5Ac T5B T5Bc T7A T6Ac T6B T6Bc T8A T7Ac T7B T7Bc ANOSIM ( Faunistic comparisons T8A T8A T8A T8A T9A T9A T9A T9A T9A T8Ac T8B T8Bc T10A T9Ac T9B T9Bc ANOSIM ( Steyaert et al (2005) also demonstrated that T. communis, which is another close species to T. longicaudata, is a typical inhabitant of poorly oxygenated sediment, which visibly supports its low oxygen requirements. In contrast, recent experiments have revealed that the Ptycholaimellus species either migrate away from anoxic spots in the sediment (Franco et al, 2008) or experience high mortality in experimental anoxic/suboxic set-ups (Steyaert et al, 2007).…”