Meiobenthos of the Deep Northeast Atlantic
Available from: Federica Semprucci
- "The richness of the meiofauna was overall comparable to the data available on similar types of habitats and in tropical regions (Gourbault & Renaud-Mornant 1990; Guo et al., 2008; Semprucci et al., 2013). The lowest abundances recorded in the Huvadhoo lagoon could be explained by the wellknown inverse trend between meiofaunal abundance and depth (Alongi & Pichon, 1988; de Bovée et al., 1990; Tietjen, 1992; Vincx et al., 1994; Sommer & Pfannkuche, 2000; Rex et al., 2006). Accordingly, Danovaro et al. (2000) documented a decline in meiofaunal abundance in the continental shelf of the Mediterranean Sea between 40 and 700 m depth. "
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ABSTRACT: Huvadhoo Atoll is a little-known and generally uncontaminated atoll of the southern Maldives, although the human pressure is increasing. This study represents the first attempt to characterize the meiofaunal and nematode assemblages of its lagoon both from a taxonomic and functional point of view. The nematode assemblage was made up of a total of 131 genera in 33 families. Desmodoridae, Chromadoridae and Xyalidae represented the richest and most abundant families, followed in terms of abundance by Selachinematidae and Comesomatidae. The nematode richness was overall higher than that reported in the previous studies carried out in the Central part of the archipelago. The diversity patterns revealed higher values than those reported for the back-reefs platforms, so confirming the positive influence of the water depth on the biodiversity of the nematode assemblage. The statistical analysis highlighted a significant taxonomic difference of the assemblages between the stations characterized by fine and medium-coarse sands, respectively, in line with the auto-ecological preferences of the taxa detected. The use of some nematode descriptors for assessing the ecological quality status (EQS) of the lagoon has revealed a slight disturbance in the station close to Viligili, one of the most urbanized islands. However, the summarization of all the descriptors used allows the highlighting of the good EQS of the Huvadhoo lagoon. Thus, the results of this study may be taken as the starting point for the future monitoring of the potential and real impact of the anthropogenic activity on the area over time.
Available from: Sabine Gollner
- "Nematode densities and biomass along the regular slope generally decrease with water depth, surface primary productivity and distance offshore , . They range between 10 individuals per 10 cm2 in the most oligotrophic seas, such as the central Arctic  or the East Mediterranean , to a maximum of several 1000 individuals per10 cm2 in the most productive areas such as the Weddell sea , or at other upwelling areas near oxygen minimum zones . "
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ABSTRACT: Here, insight is provided into the present knowledge on free-living nematodes associated with chemosynthetic environments in the deep sea. It was investigated if the same trends of high standing stock, low diversity, and the dominance of a specialized fauna, as observed for macro-invertebrates, are also present in the nematodes in both vents and seeps.
This review is based on existing literature, in combination with integrated analysis of datasets, obtained through the Census of Marine Life program on Biogeography of Deep-Water Chemosynthetic Ecosystems (ChEss).
Nematodes are often thriving in the sulphidic sediments of deep cold seeps, with standing stock values ocassionaly exceeding largely the numbers at background sites. Vents seem not characterized by elevated densities. Both chemosynthetic driven ecosystems are showing low nematode diversity, and high dominance of single species. Genera richness seems inversely correlated to vent and seep fluid emissions, associated with distinct habitat types. Deep-sea cold seeps and hydrothermal vents are, however, highly dissimilar in terms of community composition and dominant taxa. There is no unique affinity of particular nematode taxa with seeps or vents.
It seems that shallow water relatives, rather than typical deep-sea taxa, have successfully colonized the reduced sediments of seeps at large water depth. For vents, the taxonomic similarity with adjacent regular sediments is much higher, supporting rather the importance of local adaptation, than that of long distance distribution. Likely the ephemeral nature of vents, its long distance offshore and the absence of pelagic transport mechanisms, have prevented so far the establishment of a successful and typical vent nematode fauna. Some future perspectives in meiofauna research are provided in order to get a more integrated picture of vent and seep biological processes, including all components of the marine ecosystem.
Available from: Agnes Muthumbi
- "Putting this into the context of the deep sea, the mid-slope region becomes the borderline between two distinct communities (shallow and deep) and supports a high overlap of species. Examples of distinct communities from shallow and deep water are well represented in the literature (Vincx et al. 1994; Rex 1997; Vanhove et al. 1999; Muthumbi et al. 2004; Netto et al. 2005). To explain how the borderline between these two communities and the high mid-slope diversity are generated , Rogers (2000) suggests that climatic fluctuations, from warm to cold phases, over geological time scales shifted the oxygen minimum zone up and down the slope causing periodic extinctions of the abyssal fauna as well as shallow-water fauna, but had less influence on the bathyal zone. "
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ABSTRACT: This study investigated the distribution of Molgolaimus species (Nematoda) at different hierarchical spatial scales and observed the turnover of species along bathymetrical transects and among transects in two separate geographical regions. Samples from six transects (200–2000 m) from the Southern Oceans (SO) and four bathymetric transects (50–2000 m) from the Western Indian Ocean (WIO) were compared. Of the 30 species recorded, only one was common to both regions. WIO had higher local species richness than the SO. In both regions, the local scale was the greatest contributor to the total species richness. In the SO, there was no difference between species turnover at the different spatial scales, however, in the WIO, the turnover along bathymetrical transects was higher than among separated transects. For the particular genus studied, the evidence suggests that the study area in WIO has more widespread species and was better sampled, while the SO has many restricted species and it is most probably characterized by different biogeographical provinces. At the ocean scale (i.e. WIO versus SO), evolutionary histories may have strongly influenced nematodes species composition, while at local and regional scales, ecological processes are probably promoting species co-existence and speciation. The high co-existence of certain species at local scale is partially explained by species preference for different sediment layers.
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