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Size structure of marine soft-bottom macrobenthic communities across natural habitat gradients: implications for productivity and ecosystem function.

Macdonald TA, Burd BJ, van Roodselaar A - PLoS ONE (2012)

Bottom Line: These habitat variables are uncorrelated in this hydrographically diverse area, thus we examine their effects in combination and separately.When combined, habitat factors result in three distinct assemblages: (1) communities with a high proportion of biomass in small organisms, typical of shallow areas (<10 m) with coarse sediments (<10% fines) and low accumulation of organic material (<3.0 gC/m(2)/yr/δ(15)N); (2) communities with high proportion of biomass in the largest organisms found in the Strait, typical of deep, fine sediments with high modified organic flux (>3 g C/m(2)/yr/δ(15)N) from the Fraser River; and (3) communities with biomass dominated by moderately large organisms, but lacking the smallest and largest size classes, typical of deep, fine sediments experiencing low modified organic flux (<3.0 gC/m(2)/yr/δ(15)N).The ecological implications of size structure in the Strait of Georgia relative to environmental conditions, secondary production and sediment bioturbation are discussed.

View Article: PubMed Central - PubMed

Affiliation: Institute of Ocean Sciences, Department of Fisheries and Oceans, Sidney, British Columbia, Canada. tara@biologica.bc.ca

ABSTRACT
Size distributions of biotic assemblages are important modifiers of productivity and function in marine sediments. We investigated the distribution of proportional organic biomass among logarithmic size classes (2(-6)J to 2(16)J) in the soft-bottom macrofaunal communities of the Strait of Georgia, Salish Sea on the west coast of Canada. The study examines how size structure is influenced by 3 fundamental habitat descriptors: depth, sediment percent fines, and organic flux (modified by quality). These habitat variables are uncorrelated in this hydrographically diverse area, thus we examine their effects in combination and separately. Cluster analyses and cumulative biomass size spectra reveal clear and significant responses to each separate habitat variable. When combined, habitat factors result in three distinct assemblages: (1) communities with a high proportion of biomass in small organisms, typical of shallow areas (<10 m) with coarse sediments (<10% fines) and low accumulation of organic material (<3.0 gC/m(2)/yr/δ(15)N); (2) communities with high proportion of biomass in the largest organisms found in the Strait, typical of deep, fine sediments with high modified organic flux (>3 g C/m(2)/yr/δ(15)N) from the Fraser River; and (3) communities with biomass dominated by moderately large organisms, but lacking the smallest and largest size classes, typical of deep, fine sediments experiencing low modified organic flux (<3.0 gC/m(2)/yr/δ(15)N). The remaining assemblages had intermediate habitat types and size structures. Sediment percent fines and flux appear to elicit threshold responses in size structure, whereas depth has the most linear influence on community size structure. The ecological implications of size structure in the Strait of Georgia relative to environmental conditions, secondary production and sediment bioturbation are discussed.

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Response of size structure to combined habitat factors.Samples were re-categorized based on previous cluster analyses into shallow (<10 m) and deep (≥10 m), Coarse sediments (<10% fines) and Fine sediments (≥10% fines), and low organic flux (<3 gC/m2/yr/δ15N) and high organic flux (≥3 gC/m2/yr/δ15N) and analyzed together. (A) Cluster analyses show relationships among habitat categories based on their community size structure. SIGTREE analyses assess which relationships are statistically significant. Asterisks indicate p<0.0001, (and thus rejection of the  hypothesis at α = 0.01 that the two groups being linked are homogeneous). P-values >0.01 are indicated above nodes. (B) Cumulative biomass size spectra for each habitat category show how proportional biomass accumulates across size categories of macrobenthic organisms (based on log2 organic biomass). Horizontal lines are placed at 95% of total biomass and 50% of total pooled biomass.
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pone-0040071-g005: Response of size structure to combined habitat factors.Samples were re-categorized based on previous cluster analyses into shallow (<10 m) and deep (≥10 m), Coarse sediments (<10% fines) and Fine sediments (≥10% fines), and low organic flux (<3 gC/m2/yr/δ15N) and high organic flux (≥3 gC/m2/yr/δ15N) and analyzed together. (A) Cluster analyses show relationships among habitat categories based on their community size structure. SIGTREE analyses assess which relationships are statistically significant. Asterisks indicate p<0.0001, (and thus rejection of the hypothesis at α = 0.01 that the two groups being linked are homogeneous). P-values >0.01 are indicated above nodes. (B) Cumulative biomass size spectra for each habitat category show how proportional biomass accumulates across size categories of macrobenthic organisms (based on log2 organic biomass). Horizontal lines are placed at 95% of total biomass and 50% of total pooled biomass.

Mentions: Based on the above cluster analyses for individual habitat factors, samples were re-categorized into groups that reflect the maximal divergence in faunal size structure. For instance, the most distinct divergence in size structure in the cluster analysis and cumulative biomass size spectrum for depth was at 10 m, resulting in two new categories of <10 m and ≥10 m. Similarly, samples were grouped into <10% fines and ≥10% fines, and <3 gC/m2/yr/δ15N and ≥3 gC/m2/yr/δ15N. For convenience these categories can be distinguished by the terms deep/shallow, coarse/fine, and low/high flux respectively (reflecting the extremes that these categories represent). Five new combined habitat categories resulted, as not all possible combinations of habitat factors were present (Table 3). Using SIGTREE, the two most dissimilar and significantly distinct (p<0.01) community size structure groupings that emerged (Fig. 5A) were; (1) shallow, coarse, low flux samples, and (2) deep, fine, high flux samples. Both groups had significantly heterogeneous community size structure (p<0.0001). The deep/fine/low flux category (p<0.0001; Fig. 5A) also had significantly distinct size structure. The remaining two cluster groups (deep/coarse/low flux and shallow/fine/low flux) were not statistically distinguishable from each other (p = 0.025), but by extrapolation, were collectively distinct from all other cluster groupings.


Size structure of marine soft-bottom macrobenthic communities across natural habitat gradients: implications for productivity and ecosystem function.

Macdonald TA, Burd BJ, van Roodselaar A - PLoS ONE (2012)

Response of size structure to combined habitat factors.Samples were re-categorized based on previous cluster analyses into shallow (<10 m) and deep (≥10 m), Coarse sediments (<10% fines) and Fine sediments (≥10% fines), and low organic flux (<3 gC/m2/yr/δ15N) and high organic flux (≥3 gC/m2/yr/δ15N) and analyzed together. (A) Cluster analyses show relationships among habitat categories based on their community size structure. SIGTREE analyses assess which relationships are statistically significant. Asterisks indicate p<0.0001, (and thus rejection of the  hypothesis at α = 0.01 that the two groups being linked are homogeneous). P-values >0.01 are indicated above nodes. (B) Cumulative biomass size spectra for each habitat category show how proportional biomass accumulates across size categories of macrobenthic organisms (based on log2 organic biomass). Horizontal lines are placed at 95% of total biomass and 50% of total pooled biomass.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3401224&req=5

pone-0040071-g005: Response of size structure to combined habitat factors.Samples were re-categorized based on previous cluster analyses into shallow (<10 m) and deep (≥10 m), Coarse sediments (<10% fines) and Fine sediments (≥10% fines), and low organic flux (<3 gC/m2/yr/δ15N) and high organic flux (≥3 gC/m2/yr/δ15N) and analyzed together. (A) Cluster analyses show relationships among habitat categories based on their community size structure. SIGTREE analyses assess which relationships are statistically significant. Asterisks indicate p<0.0001, (and thus rejection of the hypothesis at α = 0.01 that the two groups being linked are homogeneous). P-values >0.01 are indicated above nodes. (B) Cumulative biomass size spectra for each habitat category show how proportional biomass accumulates across size categories of macrobenthic organisms (based on log2 organic biomass). Horizontal lines are placed at 95% of total biomass and 50% of total pooled biomass.
Mentions: Based on the above cluster analyses for individual habitat factors, samples were re-categorized into groups that reflect the maximal divergence in faunal size structure. For instance, the most distinct divergence in size structure in the cluster analysis and cumulative biomass size spectrum for depth was at 10 m, resulting in two new categories of <10 m and ≥10 m. Similarly, samples were grouped into <10% fines and ≥10% fines, and <3 gC/m2/yr/δ15N and ≥3 gC/m2/yr/δ15N. For convenience these categories can be distinguished by the terms deep/shallow, coarse/fine, and low/high flux respectively (reflecting the extremes that these categories represent). Five new combined habitat categories resulted, as not all possible combinations of habitat factors were present (Table 3). Using SIGTREE, the two most dissimilar and significantly distinct (p<0.01) community size structure groupings that emerged (Fig. 5A) were; (1) shallow, coarse, low flux samples, and (2) deep, fine, high flux samples. Both groups had significantly heterogeneous community size structure (p<0.0001). The deep/fine/low flux category (p<0.0001; Fig. 5A) also had significantly distinct size structure. The remaining two cluster groups (deep/coarse/low flux and shallow/fine/low flux) were not statistically distinguishable from each other (p = 0.025), but by extrapolation, were collectively distinct from all other cluster groupings.

Bottom Line: These habitat variables are uncorrelated in this hydrographically diverse area, thus we examine their effects in combination and separately.When combined, habitat factors result in three distinct assemblages: (1) communities with a high proportion of biomass in small organisms, typical of shallow areas (<10 m) with coarse sediments (<10% fines) and low accumulation of organic material (<3.0 gC/m(2)/yr/δ(15)N); (2) communities with high proportion of biomass in the largest organisms found in the Strait, typical of deep, fine sediments with high modified organic flux (>3 g C/m(2)/yr/δ(15)N) from the Fraser River; and (3) communities with biomass dominated by moderately large organisms, but lacking the smallest and largest size classes, typical of deep, fine sediments experiencing low modified organic flux (<3.0 gC/m(2)/yr/δ(15)N).The ecological implications of size structure in the Strait of Georgia relative to environmental conditions, secondary production and sediment bioturbation are discussed.

View Article: PubMed Central - PubMed

Affiliation: Institute of Ocean Sciences, Department of Fisheries and Oceans, Sidney, British Columbia, Canada. tara@biologica.bc.ca

ABSTRACT
Size distributions of biotic assemblages are important modifiers of productivity and function in marine sediments. We investigated the distribution of proportional organic biomass among logarithmic size classes (2(-6)J to 2(16)J) in the soft-bottom macrofaunal communities of the Strait of Georgia, Salish Sea on the west coast of Canada. The study examines how size structure is influenced by 3 fundamental habitat descriptors: depth, sediment percent fines, and organic flux (modified by quality). These habitat variables are uncorrelated in this hydrographically diverse area, thus we examine their effects in combination and separately. Cluster analyses and cumulative biomass size spectra reveal clear and significant responses to each separate habitat variable. When combined, habitat factors result in three distinct assemblages: (1) communities with a high proportion of biomass in small organisms, typical of shallow areas (<10 m) with coarse sediments (<10% fines) and low accumulation of organic material (<3.0 gC/m(2)/yr/δ(15)N); (2) communities with high proportion of biomass in the largest organisms found in the Strait, typical of deep, fine sediments with high modified organic flux (>3 g C/m(2)/yr/δ(15)N) from the Fraser River; and (3) communities with biomass dominated by moderately large organisms, but lacking the smallest and largest size classes, typical of deep, fine sediments experiencing low modified organic flux (<3.0 gC/m(2)/yr/δ(15)N). The remaining assemblages had intermediate habitat types and size structures. Sediment percent fines and flux appear to elicit threshold responses in size structure, whereas depth has the most linear influence on community size structure. The ecological implications of size structure in the Strait of Georgia relative to environmental conditions, secondary production and sediment bioturbation are discussed.

Show MeSH