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Macrofaunal Patterns in and around du Couedic and Bonney Submarine Canyons, South Australia.

Conlan KE, Currie DR, Dittmann S, Sorokin SJ, Hendrycks E - PLoS ONE (2015)

Bottom Line: Overall, the canyon interiors were not significantly different in community composition from the exterior (H3).However, both canyons had higher abundance and/or biomass, increased species dominance, different species composition and coarser sediments near the canyon heads compared to outside the canyons at the same depth (500 m), suggestive of heightened currents within the canyons that influence community composition there.The large number of species captured, given the relatively low sampling effort and focus on the larger macrofauna, support previous studies that identify the South Australian coast as a high biodiversity area.

View Article: PubMed Central - PubMed

Affiliation: Canadian Museum of Nature, Ottawa, Ontario, Canada.

ABSTRACT
Two South Australian canyons, one shelf-incising (du Couedic) and one slope-limited (Bonney) were compared for macrofaunal patterns on the shelf and slope that spanned three water masses. It was hypothesized that community structure would (H1) significantly differ by water mass, (H2) show significant regional differences and (H3) differ significantly between interior and exterior of each canyon. Five hundred and thirty-one species of macrofauna ≥ 1 mm were captured at 27 stations situated in depth stratified transects inside and outside the canyons from 100 to 1500 m depth. The macrofauna showed a positive relationship to depth in abundance, biomass, species richness and community composition while taxonomic distinctness and evenness remained high at all depths. Biotic variation on the shelf was best defined by variation in bottom water primary production while sediment characteristics and bottom water oxygen, temperature and nutrients defined biotic variation at greater depth. Community structure differed significantly (p<0.01) among the three water masses (shelf-flowing South Australian current, upper slope Flinders current and lower slope Antarctic Intermediate Water) (H1). Although community differences between the du Couedic and Bonney regions were marginally above significance at p = 0.05 (H2), over half of the species captured were unique to each region. This supports the evidence from fish and megafaunal distributions that the du Couedic and Bonney areas are in different bioregions. Overall, the canyon interiors were not significantly different in community composition from the exterior (H3). However, both canyons had higher abundance and/or biomass, increased species dominance, different species composition and coarser sediments near the canyon heads compared to outside the canyons at the same depth (500 m), suggestive of heightened currents within the canyons that influence community composition there. At 1000-1500 m, the canyon interiors were depauperate, typical of V-shaped canyons elsewhere. The large number of species captured, given the relatively low sampling effort and focus on the larger macrofauna, support previous studies that identify the South Australian coast as a high biodiversity area.

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Abundance (a and e), biomass (b and f), species richness (c and g) and taxonomic distinctness (d and h) at each station in Fig 2. Upper panel: du Couedic region; lower panel: Bonney region.The same scale is used for the same variable in each region.
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pone.0143921.g004: Abundance (a and e), biomass (b and f), species richness (c and g) and taxonomic distinctness (d and h) at each station in Fig 2. Upper panel: du Couedic region; lower panel: Bonney region.The same scale is used for the same variable in each region.

Mentions: Maximum abundance (3341 and 3164 ind m-2) and biomass (4343.5 and 2516.0 g m-2) occurred outside the canyons at 100 m in the du Couedic and Bonney regions, respectively (Table 3). Both abundance and biomass declined with depth to ≤10 ind m-2 and a biomass of ≤0.1 g m-2 (Table 3, Fig 4). The proportion of biomass to abundance for the solitary organisms (i.e., annelids, molluscs, arthropods, echinoderms and other solitary species) did not decline with depth. Highest proportions were at DE 500 (0.051) and BW 1500 (0.040) for the du Couedic and Bonney regions respectively. Species richness of the total macrofauna was highest at DE 100 (121 species) and BW 100 (129 species) and declined with depth to a single species at DC 1500 and BE 1500. The expected number of species from a sample of 400 individuals was highest in the du Couedic region at DC 200 (67.88) and in the Bonney region at BW 100 (94.42). Values declined with depth particularly deeper than 500 m. Shannon-Weaver diversity also declined with depth, ranging from 3.98 at DC 100 to 1.47 at DC 1000 in the du Couedic region and 4.02 at BW 100 to 1.79 at BE 1000 in the Bonney region. Community structure generally remained evenly distributed and taxonomically distinct with depth, with most values >0.8 for Pielou evenness, >0.9 for Simpson evenness and >0.8 for taxonomic distinctness. The upper reaches of both canyons at 500 m (DC 500) and (BC 500) showed lower Shannon-Weaver diversity due to higher dominance (less evenness) in the central canyon axes than outside the canyons to west or east at this depth (3.37–2.59–3.00 at du Couedic and 2.82–2.49–3.19 at Bonney for Shannon-Weaver index, 0.90–0.78–0.93 and 0.90–0.69–0.96 for Pielou index and 0.95–0.89–0.95 and 0.92–0.78–0.95 for Simpson index, for W-C-E respectively). Taxonomic distinctness was high (>75.5) at all stations with more than one species and highest where a few distantly related taxa occurred in the deep stations (90.67 at DC 1000 and 94.00 at BW 1500).


Macrofaunal Patterns in and around du Couedic and Bonney Submarine Canyons, South Australia.

Conlan KE, Currie DR, Dittmann S, Sorokin SJ, Hendrycks E - PLoS ONE (2015)

Abundance (a and e), biomass (b and f), species richness (c and g) and taxonomic distinctness (d and h) at each station in Fig 2. Upper panel: du Couedic region; lower panel: Bonney region.The same scale is used for the same variable in each region.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4664417&req=5

pone.0143921.g004: Abundance (a and e), biomass (b and f), species richness (c and g) and taxonomic distinctness (d and h) at each station in Fig 2. Upper panel: du Couedic region; lower panel: Bonney region.The same scale is used for the same variable in each region.
Mentions: Maximum abundance (3341 and 3164 ind m-2) and biomass (4343.5 and 2516.0 g m-2) occurred outside the canyons at 100 m in the du Couedic and Bonney regions, respectively (Table 3). Both abundance and biomass declined with depth to ≤10 ind m-2 and a biomass of ≤0.1 g m-2 (Table 3, Fig 4). The proportion of biomass to abundance for the solitary organisms (i.e., annelids, molluscs, arthropods, echinoderms and other solitary species) did not decline with depth. Highest proportions were at DE 500 (0.051) and BW 1500 (0.040) for the du Couedic and Bonney regions respectively. Species richness of the total macrofauna was highest at DE 100 (121 species) and BW 100 (129 species) and declined with depth to a single species at DC 1500 and BE 1500. The expected number of species from a sample of 400 individuals was highest in the du Couedic region at DC 200 (67.88) and in the Bonney region at BW 100 (94.42). Values declined with depth particularly deeper than 500 m. Shannon-Weaver diversity also declined with depth, ranging from 3.98 at DC 100 to 1.47 at DC 1000 in the du Couedic region and 4.02 at BW 100 to 1.79 at BE 1000 in the Bonney region. Community structure generally remained evenly distributed and taxonomically distinct with depth, with most values >0.8 for Pielou evenness, >0.9 for Simpson evenness and >0.8 for taxonomic distinctness. The upper reaches of both canyons at 500 m (DC 500) and (BC 500) showed lower Shannon-Weaver diversity due to higher dominance (less evenness) in the central canyon axes than outside the canyons to west or east at this depth (3.37–2.59–3.00 at du Couedic and 2.82–2.49–3.19 at Bonney for Shannon-Weaver index, 0.90–0.78–0.93 and 0.90–0.69–0.96 for Pielou index and 0.95–0.89–0.95 and 0.92–0.78–0.95 for Simpson index, for W-C-E respectively). Taxonomic distinctness was high (>75.5) at all stations with more than one species and highest where a few distantly related taxa occurred in the deep stations (90.67 at DC 1000 and 94.00 at BW 1500).

Bottom Line: Overall, the canyon interiors were not significantly different in community composition from the exterior (H3).However, both canyons had higher abundance and/or biomass, increased species dominance, different species composition and coarser sediments near the canyon heads compared to outside the canyons at the same depth (500 m), suggestive of heightened currents within the canyons that influence community composition there.The large number of species captured, given the relatively low sampling effort and focus on the larger macrofauna, support previous studies that identify the South Australian coast as a high biodiversity area.

View Article: PubMed Central - PubMed

Affiliation: Canadian Museum of Nature, Ottawa, Ontario, Canada.

ABSTRACT
Two South Australian canyons, one shelf-incising (du Couedic) and one slope-limited (Bonney) were compared for macrofaunal patterns on the shelf and slope that spanned three water masses. It was hypothesized that community structure would (H1) significantly differ by water mass, (H2) show significant regional differences and (H3) differ significantly between interior and exterior of each canyon. Five hundred and thirty-one species of macrofauna ≥ 1 mm were captured at 27 stations situated in depth stratified transects inside and outside the canyons from 100 to 1500 m depth. The macrofauna showed a positive relationship to depth in abundance, biomass, species richness and community composition while taxonomic distinctness and evenness remained high at all depths. Biotic variation on the shelf was best defined by variation in bottom water primary production while sediment characteristics and bottom water oxygen, temperature and nutrients defined biotic variation at greater depth. Community structure differed significantly (p<0.01) among the three water masses (shelf-flowing South Australian current, upper slope Flinders current and lower slope Antarctic Intermediate Water) (H1). Although community differences between the du Couedic and Bonney regions were marginally above significance at p = 0.05 (H2), over half of the species captured were unique to each region. This supports the evidence from fish and megafaunal distributions that the du Couedic and Bonney areas are in different bioregions. Overall, the canyon interiors were not significantly different in community composition from the exterior (H3). However, both canyons had higher abundance and/or biomass, increased species dominance, different species composition and coarser sediments near the canyon heads compared to outside the canyons at the same depth (500 m), suggestive of heightened currents within the canyons that influence community composition there. At 1000-1500 m, the canyon interiors were depauperate, typical of V-shaped canyons elsewhere. The large number of species captured, given the relatively low sampling effort and focus on the larger macrofauna, support previous studies that identify the South Australian coast as a high biodiversity area.

Show MeSH
Related in: MedlinePlus