Sampling seafloor sediment

Box corer coming onto deck (Photo: A. Schaap)

Macrofauna sampling and particle size analysis (PSA) are being used to create a baseline study of the macrofauna found around the Goldeneye site. We want to document the community structure and will do the sampling again following next year’s CO2 release experiment in 2019, in order to understand how the introduction of CO2 may affect it. Over 200 sites around the Goldeneye platform have been earmarked for sampling, 60 of which are of top priority. The sites have been carefully selected to represent different variables and factors including sites inside pockmarks, outside pockmarks, sandy mud sediment, muddy sand sediment, and whether or not a well head is nearby. Our approach will allow for comprehensive macro fauna sampling data of the area.

The sampling process of a site begins with collecting 0-2 cm, 2-5 cm, and 5-10 cm depth samples of the surface sediment using a syringe corer for PSA. 30 cm round sub-cores, with a depth of 30 cm, are then taken from 50×50 cm sediment box cores. These sub-cores are then portioned out into buckets, topped up with seawater, elutriated by hand to suspend the macrofauna within the buckets into the water, and poured over a large 1 mm pore size sieve inside a larger tub. Each bucket requires 3-5 elutriations to ensure that all the macrofauna, including heavy bivalves, in the portion of sub-sample in each bucket are suspended and poured into the sieve. The macrofauna that are retained by the 1 mm sieve once all elutriations have been completed, become the corresponding samples for the site where the box cores have been taken.

Sampling with syringe (Photo: A. Schaap)

 

Hi-tech bucket technology used in preparing the samples (Photo: A. Schaap)

The final sample, ready for analysis back in the lab at PML. (Photo: A. Schaap)

These samples will be analysed at a later date at Plymouth Marine Laboratory to provide important species abundance, biomass and diversity data that will help us understand the benthic ecology and macro fauna community found at each of the sampling sites. This baseline study will also allow us to make a direct comparison as to how the benthic macro fauna communities found at these sites have been affected when sampled again after the controlled CO2 release experiment in spring 2019.

Greetings from all on the ship!

Thomas Mesher

 

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