T'is the season to be sieving.....
Posted by Paul on
20 December 2011
After completing our grab and acoustic survey at the
relinquished aggregate extraction site we transited south to begin
work at the second of our surveys designed to assess the effects of
a range of human activities on the seabed (see 'Multibeam
Celebrations')
During all of our surveys we have been collecting Hamon grabs so
we can assess the infaunal communities present. When the Hamon grab
lands on the seabed it takes an image and a sample of sediment (see
below).
Before the sample is processed (to extract the infaunal species)
a photograph and a sample of the sediment are taken for sediment
Particle Size Analysis (PSA). This sample is frozen onboard in our
blast freezers before being processed back at the Cefas Laboratory.
This information is very important as it allows us to compare
habitats in different regions and also because sediment particle
size can often influence the type and number of infaunal species
present (see below).
Once we have taken the sample for PSA we extract the infaunal
species (see 'Advent of another day') by gently sieving the sample
over a 5mm and 1mm sieve (these sieve sizes will vary depending on
which fraction of the infauna is required).
Once the infauna have been extracted from the sample taken by
the Hamon grab they are preserved and then taken back to the Cefas
Laboratory for identification by benthic ecologists.
To follow our progress during the final few days of survey see
our next blog.
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