Nephin J et al. (2014), Diversity, abundance and community structure of...

ECB-ART-43501

PLoS One 2014 Jul 01;97:e101556. doi: 10.1371/journal.pone.0101556.

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Diversity, abundance and community structure of benthic macro- and megafauna on the Beaufort shelf and slope.

Nephin J , Juniper SK , Archambault P .

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Diversity and community patterns of macro- and megafauna were compared on the Canadian Beaufort shelf and slope. Faunal sampling collected 247 taxa from 48 stations with box core and trawl gear over the summers of 2009-2011 between 50 and 1,000 m in depth. Of the 80 macrofaunal and 167 megafaunal taxa, 23% were uniques, present at only one station. Rare taxa were found to increase proportional to total taxa richness and differ between the shelf (< 100 m) where they tended to be sparse and the slope where they were relatively abundant. The macrofauna principally comprised polychaetes with nephtyid polychaetes dominant on the shelf and maldanid polychaetes (up to 92% in relative abundance/station) dominant on the slope. The megafauna principally comprised echinoderms with Ophiocten sp. (up to 90% in relative abundance/station) dominant on the shelf and Ophiopleura sp. dominant on the slope. Macro- and megafauna had divergent patterns of abundance, taxa richness (α diversity) and β diversity. A greater degree of macrofaunal than megafaunal variation in abundance, richness and β diversity was explained by confounding factors: location (east-west), sampling year and the timing of sampling with respect to sea-ice conditions. Change in megafaunal abundance, richness and β diversity was greatest across the depth gradient, with total abundance and richness elevated on the shelf compared to the slope. We conclude that megafaunal slope taxa were differentiated from shelf taxa, as faunal replacement not nestedness appears to be the main driver of megafaunal β diversity across the depth gradient.

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Genes referenced: LOC100887844 LOC100893907

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	Figure 1. Sampling stations and ice coverage on the Beaufort shelf and slope from 2009 to 2011.One box core and trawl sample were collected from each station (left panel). Sample sizes were nâ€Š=â€Š18 in 2009, nâ€Š=â€Š18 in 2010 and nâ€Š=â€Š12 in 2011. Black dotted line outlines the spatial extent of sampling used to calculate the average slope. Ice coverage (white area, right panel) for 2009, 2010 and 2011 benthic sampling periods. Blue coverage area outlines the area over which ice coverage was calculated. Blue lines in plots represent historic ice coverage (median from 1981 to 2010). Green bars indicate when benthic sampling occurred. Ice coverage data courtesy of Canadian Ice Service, Environment Canada.
	Figure 2. Distribution of occurrence.(A) Distribution of occurrence as percent of sites occupied (binned intervals starting with 1-10%) and (B) mean relative abundance (%) by percent of sites occupied. Relative abundance, a measure of local abundance, was averaged only across sites where taxa were present. Vertical grey line represents rarity cut-off at 10% and horizontal grey line denotes the median average relative abundance. Spearman's rank correlation coefficient denoted by
	Figure 3. Proportion of rare taxa unique to or shared between shelf and slope.The proportion of low or highly abundant rare taxa sampled only on the shelf, slope or both localities. Rare taxa defined as taxa occurring at 10% of sites or less. Uniques (taxa which were sampled only at one site) are distinguished from other rare taxa. High and low relative abundance defined as greater or lower than the median.
	Figure 4. Relationships of total macro- and megafaunal abundance with depth.Abundance in number of individuals per sample. Sample area of macrofauna: 0.125 m2 and megafauna: 450 m Spearman's rank correlation coefficient denoted by
	Figure 5. Comparison of macrofaunal (light blue) and megafaunal (dark blue) abundance and taxa richness between shelf and slope stations and sampling years.Mean total abundance (left panel) and mean taxa richness (right panel). Stations grouped by shelf and slope (top panel) and stations grouped by year on shelf or slope (bottom panels). Bars represent 95% confidence intervals. Sample size (N) is denoted by number on bar. Sample area of macrofauna: 0.125 m2 and megafauna: 450 m
	Figure 6. Individual-based rarefaction curves for 2009 and 2010 megafaunal datasets.(A) non-normalized counts and (B) counts normalized to the average trawl area. Curves represent the average of 900 resampling permutations.
	Figure 7. diversity across the depth gradient. diversity as a comparison of Bray-Curtis similarity between each pairwise depth difference. Spearman's rank correlation coefficient and significance (p-value) denoted by and p, respectively.
	Figure 8. Dendrogram and nMDS ordination of station similarities.Hierarchical, Ward's method cluster dendrogram (top) and nMDS ordination highlighting clusters and sampling year (bottom) both derived from Bray-Curtis dissimilarity of macrofaunal and megafaunal abundance matrices. Average silhouette widths (scale ) noted atop each cluster. Coloured circles in ordination represent macro- and megafaunal clusters defined in dendrograms. Circle sizes correspond to sample years indicated on right.
	Figure 9. Map of Beaufort sampling region with georeferenced clusters.Colours represent macro- and megafaunal clusters defined in dendrograms (Figure 8).
	Figure 10. Relative abundance and depth ranges of dominant taxa.Average relative abundance of dominant taxa by cluster (left). Dominant taxa ordered by their contribution to average relative abundance in clusters A, B, C and D, are highlighted by cluster to illustrate the relative contribution of taxa to each cluster. Colours represent faunal clusters defined in dendrograms (Figure 8). Depth range of corresponding taxa (right); grey circles denote mean depth of samples where taxa were present.

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