East Anglia Offshore Windfarm: Zonal Environmental Assessment Benthic Report
When large numbers of sampl es are analysed, or datasets that include samples that are ver y different to one another the accuracy of the two-dimensional plot may be reduced. A measure of the accuracy of the two-dimensional representation (stress) i s given on the MDS plot.
Stress values <0.1 corr espond to a good ordination; values <0.2 give a usefu l two- dimensional picture but one should not place too much reliance on the fi ne details of the plot; stress >0.3 indicates that the samples are close to being positioned in an arbitrary manner and shoul d not be r egarded as necessarily similar to one another, particularly in the upper half of this range.
The SIMPER Routine Analysis of Similarity (ANOSIM)
The SIMPER routine allows the i dentification and comparison of groups of sampl es. The SIMPER routine provides information on which factors are responsible for the within- group similarities and provides insight into the composition of the g roups through the provision of summary statistics relating to the factors which drive the internal similarity of groups i dentified at a gi ven statistical level.
Following the identification of groups within a given dataset the SIMPE R routine provides insight into the species (or particle size fractions) responsible for the di ssimilarity between groups. The sp ecies are li sted in decreasing order of i mportance to group dissimilarity.
This is used to test the null hypothesis (Ho) that there are no di fferences in community (or sediment) composition between pooled sample categories. The results expressed represent the extent of the si milarities and differences between pooled data. Note that an ANOSIM test returns two val ues. An R statistic and a significance value.
R Statistics approaching zero = very slight differences & therefore a hig h degree of overlap between the groups
R Statistics of 0.2-0.3 – some difference but still with some degree of overlap between the groups
R Statistics approaching 1 (>0.5) = large differences & therefore only slight overlap between the groups
Significance values of <5% indicate the return of a statistically significant result.
B.7 GIS
All of the GIS maps used in this report were generated using ArcGis 9.3.1. The WGS84 datum and UTM degrees N proj ection were used throughout.
Matching Two Multivariate Patterns (Bio-Env and Relate)
The RELATE routine provides a me ans of testing for correl ations between two multivariate patterns within two different, but potentially related datasets. RELATE tests are used to t est for correl ations between the distribution of biological communities and the distribution of sediment types.
The BIO-ENV sub-routine is an exploratory tool that matches mul tivariate patterns s o that combinations of variables are considered at ever i ncreasing levels of compl exity in order to fi nd the BEST s ub-set of vari ables that match wi th the bi ological patterns observed in the data.
