65.
The sea bed across the offshore cable corridor is predominantly sand. The median sediment grain size (d50) of a series of grab samples mostly ranges from 0.23 to 0.50mm (medium sand) with a small number of samples with a d50 in the coarse sand or very fine sand classes. Further information on sediments is presented in Chapter 7Marine Geology, Oceanography and Physical Processes and in particular Appendix 7.2. Sea bed sediments are displayed in Figure 10.2
66. Multivariate analysis of the samples collected during the East Anglia Zone Survey found that there was a significant relationship between biological communities and sediment type (Appendix 10.2).
10.5.2 Infaunal Communities 67.
In the following sections, infauna (as sampled by grabs) is taken to mean species that live in, or partially buried within, and below the sediment. Epifauna (sampled by benthic trawls) is taken to mean species that live on the surface. All fish (including sandeels) and cephalopods (squid and cuttlefish) species have been removed from the benthic and epibenthic data set as they are not considered to be benthic species. These data however are incorporated into Chapter 11 Fish and Shellfish Ecology.
10.5.2.1 Infaunal communities in the East Anglia Zone 68.
Abundance of individuals in the infauna ranged from 2240 (station 441, Zone survey) to 2 (station 41 in the East Anglia THREE / FOUR survey and station 35 in the East Anglia ONE offshore cable corridor survey). Infaunal abundance varies across the East Anglia Zone with generally higher values recorded in the west of the zone and along the offshore cable corridor (Figure 10.3).
69.
Species richness across the East Anglia Zone (identified as the number of different species found at each grab sample site) ranged from 70 (station 100 in the East Anglia Zone survey) to 2 (at station 41 in the East Anglia THREE / FOUR survey and station 35 in the East Anglia ONE offshore cable corridor survey). The pattern of species diversity was less defined than abundance with midrange values across most of the East Anglia Zone (Figure 10.4).
70. 71.
Biomass (ash free dry weight) follows a slightly different pattern with the largest values occurring in the eastern side of the zone Figure 10.5.
As detailed in section 10.4.2.2 several different primary data sets have been collected from the East Anglia Zone, East Anglia ONE export cable corridor survey and East Anglia THREE / FOUR survey. In order to characterise infaunal communities across all of these data sets, grab samples that had not been located to target specific features were combined to create larger data set and subsequently
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 10 Benthic Ecology Page 31
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