Biodiversity response to experimental induced hypoxic-anoxic conditions in seagrass sediments

Abstract

The effects of induced hypoxic-anoxic conditions on the metazoan meiofaunal assemblages and nematode diversity were investigated with an in situ experiment in a Posidonia oceanica meadow. The experiment, of the duration of five months, was performed in three experimental sets of plots. Two of them were enriched with organic matter to induce anoxic conditions (1 set with sucrose and 1 set with sugar plus nutrients, i.e. nitrogen and phosphorus) whereas the last set of plots was kept undisturbed and used as Control. Metazoan meiofauna displayed a fast response to the induced anoxic conditions with an immediate reduction of the richness of taxa (only nematodes and copepods tolerated the hypoxic-anoxic conditions). Nematodes were the most tolerant organisms as their species richness did not change in hypoxic-anoxic conditions, but their species composition and trophic structure displayed significant changes. Some genera (Desmoscolex and Bolbolaimus) were replaced by other (Chromadorella, Sabatiera and Polysigma) more tolerant to the extreme conditions. No significant differences were observed in the Control plots, whereas in treated plots, selective deposit feeders and predators decreased significantly, being replaced by non-selective deposit feeders and epistrate feeders. These results indicate that, events causing a reduction in oxygen availability, can have an impact on the nematode beta-diversity and functional diversity with potential important implications on the benthic food web and functioning of the seagrass systems.

Nematode assemblage response to fish-farm impact in vegetated (Posidonia oceanica) and non‑vegetated habitats

“…Nematode assemblages in the present study comprised a relatively high number of species, but with a few dominant ones, as observed in other coastal environments, either in non-vegetated (Soetaert et al 1995) or seagrass sediments , Gambi et al 2008. We report here, moreover, that some species were apparently highly sensitive to the organic pollution derived from fish farms.…”

A comparative analysis of benthic nematode assemblages from Zostera noltii beds before and after a major vegetation collapse

“…Nematodes belonging to the aforementioned genera are often tolerant to hypoxic conditions (Jensen, 1984;Steyaert et al, 2007) and their slender bodies may be advantageous to glide through and over the fine sediments (Warwick, 1971), even though some papers have suggested that long slender bodies are more efficient to take up oxygen through diffusion (Fleeger et al, 2011;Soetaert et al, 2002). In this study, Terschellingia and Paracomesoma were the two most abundant genera registered both before and after the Z. noltii collapse; both are able to thrive in naturally and anthropogenically disturbed, oxygen-poor habitats (Alves et al, 2013;Armenteros et al, 2009;Gambi et al, 2009;Moreno et al, 2008;Steyaert et al, 2007). Their tolerance to low oxygen conditions may at least partly explain their prominence in seagrass beds.…”

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.…”

“…As species or genus composition is comparatively more sensitive to any disturbance [21], Nematodes have already been employed in biomonitoring studies and resulted suitable indicators for pollution-induced disturbances of benthic ecosystems [e.g., [22][23][24][25][26]. To date, very few studies investigated meiofaunal organisms of P. oceanica meadows [20,[27][28][29][30][31][32].…”