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Multivariate analysis of community structure - The complete species matrices were used for multivariate analyses and these are summarised in Table 6.3. In total, 15 species colonised the azoic sediments within 3 weeks, although the majority of these were found in very low numbers. Pygospio elegans (adult) Eteone cfflava Pygospio elegans (juvenile) Anaitides mucosa Capitella capitata Glycera tridactyla Cerastoderma edule Scoloplos armiger Macoma balthica Fabulina fabula Polydora cornuta Nephtys hombergii Streblospio benedicti oligochaetes Spio martinensis polynoids Table 6.3 : Total species list from patch and non-patch azoic samples for all three experiments. The dendrograms produced by hierarchical agglomerative clustering, together with the 2-dimensional ordination plots produced by non-metric MDS of the resulting communities from the April, August and December experiments are given in Figures 6.5-6.12. The stress values associated with these MDS ordinations varied from 0.04 to 0.18. Although there is no critical cut-off value for stress values above which a species matrix cannot be represented adequately in a 2-dimensional MDS plot, the lower the stress the better. Warwick and Clarke (1994) suggested that stress values between 0.1-0.2, as the majority of those in the present study, give 'only potentially useful 2-dimensional pictures'. Under these circumstances, they recommended that the MDS plot should be complemented with other techniques such as clustering. Therefore, for ordinations with stress values between 0.1-0.2 dendrograms are included since they can potentially aid interpretation of the MDS plots. However, superimposition of the cluster groups at arbitrary similarity levels from the dendrograms onto the ordination plots, as outlined by Warwick and Clarke (1994), was not performed since this tends to add discrete subdivisions onto a community continuum. To investigate community differences between patches and non-patches, 149
circles enclosing treatments were drawn where the degree of overlap is a reflection of the community similarities/differences between them. These were statistically analysed by One-way ANOSIM tests (Table 6.4). In April, the invertebrate faunal communities of 5 out of the 6 patch replicates occurred in the same cluster at 70% similarity (Figure 6.5). This suggests that in April, colonisation of disturbed sediments within P.elegans patches resulted in distinctly different initial communities compared with those in non-patch areas. The MDS plot supported this, there was no overlap between the clusters formed by the 2 plot types (Figure 6.6). The results of the One-way ANOSEVI test also suggested this, the test being statistically significant with a p-value of 0.2% and a test statistic of 0.367. There appeared to be greater replicate variability in the community assemblages in the non-patch sediments compared to patch sediments, the replicates of the former creating 3 clusters at 71% similarity. Although the initial community structure in patches and non-patches were different to each other in August, the distinction was not as marked as that observed in April. The dendrogram presented in Figure 6.7 suggested that patch replicates 1 and 5 showed some similarity to non-patch communities. This is supported by the MDS plot (Figure 6.8) in which the 2 clusters have a large overlap. The p value for the One-way ANOSIM test was 4.3%. However, in view of the lack of compensation for multiple testing, and an R value of only 0.250, this is not considered significant. In December, no statistical differences between patch and non-patch communities were observed (p=35.5% and R=0.028; One-way ANOSIM, Table 6.4). Figure 6.9 shows that at 70% similarity, a large cluster is formed containing 5 of the non-patch replicates and 3 patch replicates. Figure 6.10 shows that there is a large overlap between the clusters formed by the 2 plot types in an MDS plot. 150
- Page 114 and 115: Pygospio elegans size distribution
- Page 116 and 117: used, approximately equivalent to t
- Page 118 and 119: artefacts associated with the metho
- Page 120 and 121: present in high numbers around sewa
- Page 122 and 123: lack, hydrogen sulphide-smelling se
- Page 124 and 125: CHAPTER 5 THE EFFECTS OF MACROALGAL
- Page 126 and 127: METHODS Survey design - During late
- Page 128 and 129: The sediments could not be sampled
- Page 130 and 131: RESULTS Species abundances - Table
- Page 132 and 133: 90 — 80 — "-e-' 70 — 60 — 4
- Page 134 and 135: 35 — *** 30 25 — 1.) = .-c‘l
- Page 136 and 137: Pygospio elegans size distributions
- Page 138 and 139: which is difficult to compare with
- Page 140 and 141: eason why some invertebrates showed
- Page 142 and 143: This study did not set out to expli
- Page 144 and 145: This reliance upon the early establ
- Page 146 and 147: CHAPTER 6 INITIAL COLONISATION OF D
- Page 148 and 149: esulting community at any stage of
- Page 150 and 151: ambient sediment had been removed.
- Page 152 and 153: emoved since they were the only tax
- Page 154 and 155: All statistics were performed using
- Page 156 and 157: RESULTS Univariate analysis of spec
- Page 158 and 159: 3.5 3 5 2 11 5 1 0.5 0 40 35 Ca 30
- Page 160 and 161: of non-patch areas (Figure 6.3(vi))
- Page 162 and 163: the individuals colonising patch az
- Page 166 and 167: Month Sample statistic (Global R) N
- Page 168 and 169: 2NP 3NP 4NP .•,, 6NP 5NP 6P 1NP i
- Page 170 and 171: Figure 6.8: Two-dimensional MDS ord
- Page 172 and 173: - - 5P ... 4P . 6P • .‘2NP 1NP
- Page 174 and 175: I 50. 1 60. 70. 80. 90. 100. BRAY-C
- Page 176 and 177: 'P2-AZ P3-AZ N2-AZ .- - - " .„ ..
- Page 178 and 179: o • o -o + 350 — 300 = 250 7 g
- Page 180 and 181: The importance of the ambient commu
- Page 182 and 183: In April, when P. elegans larval av
- Page 184 and 185: not only for errant polychaetes, bu
- Page 186 and 187: observed in this study. How crucial
- Page 188 and 189: Micro-scale spatial patterns of mac
- Page 190 and 191: METHODS Experimental design - A pre
- Page 192 and 193: study. These individuals would not
- Page 194 and 195: RESULTS Pilot survey - The pilot su
- Page 196 and 197: Transect survey - Micro-scale patte
- Page 198 and 199: Month v:m ratio pattern Id pattern
- Page 200 and 201: (i) March 1997, replicate 1 -iAlmiA
- Page 202 and 203: (xix) October 1997, replicate 1 (ra
- Page 204 and 205: The new recruits were only sufficie
- Page 206 and 207: The results of correlation analyses
- Page 208 and 209: cf.) . crt N ,—, Cr) C,1 ,—, Cr
- Page 210 and 211: 1.2 -0.4 "a 0.8 > (i) % Water conte
- Page 212 and 213: examine the micro-scale spatial pat
circles enclosing treatments were drawn where the degree of overlap is a reflection of<br />
the community similarities/differences between them. These were statistically<br />
analysed by One-way ANOSIM tests (Table 6.4).<br />
In April, the invertebrate faunal communities of 5 out of the 6 patch replicates<br />
occurred in the same cluster at 70% similarity (Figure 6.5). This suggests that in<br />
April, colonisation of disturbed sediments within P.elegans patches resulted in<br />
distinctly different initial communities compared with those in non-patch areas. The<br />
MDS plot supported this, there was no overlap between the clusters formed by the 2<br />
plot types (Figure 6.6). The results of the One-way ANOSEVI test also suggested this,<br />
the test being statistically significant with a p-value of 0.2% and a test statistic of<br />
0.367. There appeared to be greater replicate variability in the community<br />
assemblages in the non-patch sediments compared to patch sediments, the replicates<br />
of the former creating 3 clusters at 71% similarity.<br />
Although the initial community structure in patches and non-patches were different to<br />
each other in August, the distinction was not as marked as that observed in April. The<br />
dendrogram presented in Figure 6.7 suggested that patch replicates 1 and 5 showed<br />
some similarity to non-patch communities. This is supported by the MDS plot<br />
(Figure 6.8) in which the 2 clusters have a large overlap. The p value for the One-way<br />
ANOSIM test was 4.3%. However, in view of the lack of compensation for multiple<br />
testing, and an R value of only 0.250, this is not considered significant.<br />
In December, no statistical differences between patch and non-patch communities<br />
were observed (p=35.5% and R=0.028; One-way ANOSIM, Table 6.4). Figure 6.9<br />
shows that at 70% similarity, a large cluster is formed containing 5 of the non-patch<br />
replicates and 3 patch replicates. Figure 6.10 shows that there is a large overlap<br />
between the clusters formed by the 2 plot types in an MDS plot.<br />
150
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