As the full extents of East Anglia THREE and FOUR were surveyed for benthic and epibenthic surveys during the Zonal Characterisation Survey (MESL, 2011), GIS was used to identify which of the stations sampled fell within those areas. Subsequently we derived Shannon (H’) and Simpson (S) diversity indices for East Anglia THREE and FOUR followed by overall mean and standard deviations of these indices to allow conversion of es to EDPC (see Section 2.2) and undertake power analysis. This analysis allowed us to determine whether further sampling effort was required to characterise the benthic and epibenthic assemblages present.
As certain sections of the cable corridor are located within the navigational channel at the centre of the Zone, a full suite of stations encompassing the entire corridor was not available. Based on the overall density of stations/km2 (0.13km2 for benthic stations and 0.01km2 for epibenthic stations) carried out in the 2010 survey (MESL 2011), it was therefore estimated that 71 benthic stations and 6 epibenthic stations would have had to be surveyed to provide complete coverage of the corridor.
To derive means and standard deviations for the cable corridor, 71 and 6 sites respectively were chosen at random and the Shannon (H’) and Simpson (S) diversity indices calculated. These indices incorporate information on the number and abundance of species and the relative abundance of species in an assemblage (termed evenness). These measures are routinely employed to characterise ecological communities. These indices were used to derive the necessary descriptive statistics for the cable corridor. We felt a randomised approach to derive the necessary information was valid as the entire Zone was characterised by high levels of homogeneity, both in terms of ecological communities and substrate (MESL, 2011). This approach using randomly assigned, but relevant, data is also described in Quinn and Keough (2004).
Power analyses tailored towards t-tests were carried out using R (www.R.project,org), based on the proposed null hypothesis that there will be no difference in community diversity between the communities sampled during the 2010 survey (MESL 2011) and potential survey(s) carried out post-development.
