Predictability of marine nematode biodiversity

In this paper, we investigated: (1) the predictability of different aspects of biodiversity, (2) the effect of spatial autocorrelation on the predictability and (3) the environmental variables affecting the biodiversity of free-living marine nematodes on the Belgian Continental Shelf. An extensive historical database of free-living marine nematodes was employed to model different aspects of biodiversity: species richness, evenness, and taxonomic diversity. Artificial neural networks (ANNs), often considered as “black boxes”, were applied as a modeling tool. Three methods were used to reveal these “black boxes” and to identify the contributions of each environmental variable to the diversity indices. Since spatial autocorrelation is known to introduce bias in spatial analyses, Moran's I was used to test the spatial dependency of the diversity indices and the residuals of the model. The best predictions were made for evenness. Although species richness was quite accurately predicted as well, the residuals indicated a lack of performance of the model. Pure taxonomic diversity shows high spatial variability and is difficult to model. The biodiversity indices show a strong spatial dependency, opposed to the residuals of the models, indicating that the environmental variables explain the spatial variability of the diversity indices adequately. The most important environmental variables structuring evenness are clay and sand fraction, and the minimum annual total suspended matter. Species richness is also affected by the intensity of sand extraction and the amount of gravel of the sea bed

High spatiotemporal variability in meiofaunal assemblages in Blanes Canyon (NW Mediterranean) subject to anthropogenic and natural disturbances

14 páginas, 6 tablas, 4 figurasWe investigated the natural and anthropogenic drivers controlling the spatiotemporal distribution of the meiofauna in the submarine Blanes Canyon, and its adjacent western slope (NW Mediterranean margin of the Iberian Peninsula). We analyzed the relationships between the main sedimentary environmental variables (i.e. grain size, Chl-a, Chl-a: phaeopigments, CPE, organic carbon and total nitrogen) and the density and structure of the meiofaunal assemblages along a bathymetric gradient (from 500 to 2000 m depth) in spring and autumn of 2012 and 2013. Twenty-one and 16 major taxa were identified for respectively the canyon and slope, where the assemblages were always dominated by nematodes. The gradual decreasing meiofaunal densities with increasing depth at the slope showed little variability among stations and corresponded with a uniform pattern of food availability. The canyon was environmentally much more variable and sediments contained greater amounts of food resources (Chl-a and CPE) throughout, leading not only to increased meiofaunal densities compared to the slope, but also different assemblages in terms of composition and structure. This variability in the canyon is only partly explained by seasonal food inputs. The high densities found at 900 m and 1200 m depth coincided with significant increases in food availability compared to shallower and deeper stations in the canyon. Our results suggest that the disruption in expected bathymetric decrease in densities at 900–1200 m water depth coincided with noticeable changes in the environmental variables typical for disturbance and deposition events (e.g., higher sand content and CPE), evoking the hypothesis of an anthropogenic effect at these depths in the canyon. The increased downward particle fluxes at 900–1200 m depth caused by bottom trawling along canyon flanks, as reported in previous studies, support our hypothesis and allude to a substantial anthropogenic factor influencing benthic assemblages at these depths. The possible relationships of the observed patterns and some major natural environmental (e.g., surface productivity or dense shelf water cascading) and anthropogenic (e.g. the lateral advection and downward transport of food-enriched sediments resuspended by the daily canyonflank trawling activities) drivers are discussed.This research has been supported by DOS MARES (Ref. CTM2010-21810-C03-03) research project, funded by the Spanish State Research Plan, and to the Consolidated Research Group on Marine Benthic Ecology of the “Generalitat de Catalunya (2014SGR120)”. C. Romano received funding from the People Programme (Marie Curie Action) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreement N. PIOF-GA-2013-628146. J. Ingels was supported by a Plymouth Marine Laboratory Post-doctoral Research Fellowship in collaboration with University of Exeter and a Marie Curie Intra-European Fellowship within the 7th European Commission Framework Programme (Grant Agreement FP7-PEOPLE-2011-IEF no. 00879).Peer reviewe

"Belgica" Mounds in Porcupine Seabight, NE Atlantic: Biological Zonation and Environmental Control

The Belgica mounds are located on the eastern slope of Porcupine Basin between 51°10'N - 51°35'N and 11°30'W-11°45'W in water depths of 600 m to 900 m. Outcropping mounds are located on the steepest part of the slope between 750 m and 850 m. They are largest in the south and decrease in size to the north where the slope is gentler. These larger mounds merge into composite mounds up to 190 m high, 2 km to over 4 km long and have a width between 500 m - 1000 m. The eastern upslope flank of seafloor mounds is ponded with sediment while the entire western, downslope flank of the mounds remains exposed. Despite the evident asymmetry in depositional environment at both sides of a mound, Belgica mounds appear conical on seismic profiles, with an average slope of 10-15°. The base of the Belgica mounds is formed by a continuous erosional surface, probably of Miocene age. The deeply incised substratum features a very faintly stratified seismic facies and is absent in the northern part of the province. It is underlain by a sequence of sigmoidal deposits. This start-up event suggests drastic environmental changes that favoured coral growth at a certain period. Such changes may have been triggered by changes in the oceanographic circulation patterns. The mounds are associated with features related to strong currents. Zonation and biodiversity of the present coral banks was investigated by means of a videotransect and boxcoring across some of the mounds. Mainly the basinward flanks of the mounds showed patchy Lophelia communities in association with a diverse epifauna of mainly sponges and polychaetes. Along these flanks the biological communities showed a symmetrical zonation pattern. Frequently, a small patch of living Lophelia midway the mound slope grades on either side into a dead coral zone that finally turns into a coral rubble zone

Revealing species assembly rules in nematode communities

Species assemblages are not randomly assembled from a local species pool; they often show segregated or aggregated distribution patterns. These patterns may be attributed to both biotic and abiotic factors. On a large scale abiotic factors may be important, while on a smaller scale other factors such as species interactions may become essential. Here we will focus on small-scale patterns in nematode communities. Species patterns are generally revealed by null models based on presence/absence data. Since there is an increasing chance of falsely rejecting the null hypothesis of a random assembled community with increasing matrix size, we used an algorithm generating independent null matrices and applied a large number of swap attempts to build a null matrix. Moreover, we applied an additional test to reveal the susceptibility of the analyses of checker and the C-, T- and Vscore to a Type I error for randomised data. To minimise the influence of the abiotic environment, we restricted the swapping algorithm of the null model to the replicate samples of one sampling event. Since stronger species interactions are expected for species of the same functional type, the nematode data was split according to the four feeding types defined by Wieser (1953). Our data indicate that species tend to aggregate and co-occur more often in some replicate samples than would be expected from a random species distribution of the local species pool. This is in accordance with the patchy distribution patterns known for nematode species. These aggregated patterns are also found for the different feeding types. The factors causing these aggregated patterns cannot be established since they are not included in the data, but the data do indicate that competitive exclusion is unlikely at the scale of a sample core

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Mapping nematode diversity in the Southern Bight of the North Sea

In order to protect the biodiversity of the seas from, e.g., overexploitation, the spatial distribution of biodiversity and the mapping of biodiversity hotspots are of great importance. In the present paper we discuss different methods to develop full coverage biodiversity maps of free-living marine nematodes in the Southern Bight of the North Sea. A database with sampling data, gathered over 3 decades (1972 to 2004), combined with exhaustive environmental data, was employed to predict species richness and the expected number of species by different methods: ordinary kriging (OK) and regression kriging (RK) with ordinary least squares (OLS) and generalised least squares (GLS). The predictive value of these methods was evaluated by an independent validation set. Replicate samples were used to make an accurate estimation of the nugget variance, since replicates reveal local variability. Accordingly, it was feasible to find a spatial pattern in the residuals of the regression models. Our analysis pointed out that GLS improved the OK models substantially, while RK only slightly improved the GLS model. The diversity of marine nematodes is substantially influenced by the silt-clay fraction and the amount of total suspended matter, which is also reflected in the resulting map with a species-poor area near the coast line, especially near the south of the mouth of the Scheldt estuary. Off coast diversity and evenness are generally higher