Top‐down impact of bacterivorous nematodes on the bacterial community structure: a microcosm study

Abstract

The influence of bacterivorous nematodes (Diplolaimelloides meyli, Diplolaimelloides oschei, Diplolaimella dievengatensis, Panagrolaimus paetzoldi) on the development of a bacterial community growing on decaying cordgrass detritus was studied in laboratory microcosm experiments. Cordgrass leaves were incubated on a sediment surface with a natural bacterial mixture containing bacteria from sediment, cordgrass detritus and habitat water. The four nematode species were applied separately to the microcosms; controls remained without nematodes. Samples were taken seven times over a 65-day period. The bacterial community structure was analysed by means of DGGE of the 16S rRNA genes. Multi Dimensional Scaling showed grouping of the samples per treatment. Analysis of Similarities indicated that the differences between treatments were significantly larger than differences within treatments. Our results suggest that nematodes can have a significant structuring top-down influence on the 'pool' of bacteria growing on the detritus, even at low densities. Dissimilarities were similar between all treatments. Differences in bacterial community composition within the treatments with monhysterids (D. meyli, D. oschei and D. dievengatensis) can be explained by species-specific food preferences. Panagrolaimus paetzoldi on the other hand feeds unselectively, and thus affects the bacterial community differently. A top-down effect of the nematodes on the diversity of the bacterial community was only evident under high grazing pressure, i.e. in the presence of P. paetzoldi.

The faunal role in the degradation of the common intertidal salt marsh plant Scirpus maritimus

“…In addition, as summarized by DeMesel and others (2004), nematodes (meiofauna), by a direct effect of grazing on bacteria, by contributing to sediment bioturbation, to the physical breakdown of detritus and by excreting nutrients for bacteria, may stimulate detritus mineralization. Microcosmos experiments have suggested that, even at low densities, nematodes can have a significant structuring top-down influence on the bacteria growing on the cordgrass leaves detritus (DeMesel et al, 2004). Macrofauna may also feed directly on bacteria, and species such as Hydrobia ulvae, through their feeding activities on leaf surfaces (Barnes & Hughes, 1988;Lillebø et al, 1999b), might contribute to the stimulation of microbial activity.…”

“…In fact, it has been shown for other plant species that, in undisturbed marsh sediments, the major fate of below-ground production appears to be microbial decomposition (Benner et al, 1997), although the presence of meiofauna may also enhance the degradation (e.g. DeMesel et al, 2004).…”

Ecology of Marine Meiofauna

“…Essa seletividade pode modificar os valores médios de consumo da meiofauna tanto em escala local quanto temporal. O estudo de De Mesel et al (2004) realizado em microcosmos testando as preferências alimentares de várias espécies de Nematoda da ordem Monhysterida, resultou em uma captação de alimentos diferentes do que quando foram testadas cada espécie isoladamente. A seletividade e a flexibilidade tróficas são vantajosas a partir de uma perspectiva evolucionária, uma vez que podem impedir a concorrência interespecífica por presas.…”

Integrating Different Organizational Levels in Benthic Biodiversity – Ecosystem Functioning (BEF) Studies

“…De Mesel et al (2003, 2004, 2006 studied the impact of bacterivore nematodes on the bacterial community and the decomposition of cordgrass leaves. They found that four different bacterivore nematode species have a significant top-down effect on the structure of the bacterial community (De Mesel et al, 2004). However, species richness within the guild of bacterivore nematodes did not enhance decomposition rates, rather the process depended on species identity and on unexpected inhibitory and facilitative interactions among species within the same guild (De Mesel et al, 2003, 2006.…”