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Grab it, Dredge it, Weigh it: Investigating benthic size spectra

Published: 27 July 2016

It’s only been a year since I joined MERP, yet already I have spent two whole months working at sea exploring benthic ecosystems in the Celtic Sea. Using Bangor University’s Research Vessel, The Prince Madog, we have sampled all across Devon, Cornwall, Bristol Channel and Pembrokeshire. By deploying a series of grabs, dredges and nets we have managed to capture the full size spectra of animals living on the seabed ranging in size from the tiniest nematode worm to the largest cod.


As a reward for all our efforts, we have managed to weigh a total of 44,000 individual animals weighing a total of 700kg. Believe when I say, that is a lot of worms and fish! The variation in the samples has been astounding. Some have been dominated almost by a single species, such as grey gurnards or brittle stars, whilst others have brought up more interesting species such as Thornback rays, Starry smooth hounds, Conger eels and the curiously disgusting Neanthes fucata, a large rag worm that lives in the shell of hermit crabs feeding on its hosts faeces and eggs.


Size spectra of starfish

Despite our best efforts at seas, the hard work still remains. We have managed to bring back 2000 litres worth of sediment from the seabed, containing a plethora of small nematodes and crustaceans. All of these now need to be carefully identified and weighed in our labs back at Bangor University and Plymouth Marine Laboratory.

As our survey sampled sites across a gradient of fishing pressure and primary productivity (i.e. the amount of algae in the water - which are at the base of the marine food chain), we can see just how important the impacts of fishing are on benthic ecosystems, or whether natural processes such as primary productivity remain the most important controlling factors. In addition, we surveyed across two different months; September and April. Meaning we can explore the importance of seasonal influence.

Once are analyses are complete, our results will then be supplied to other MERP scientists who require the data in order to construct their ecosystem models.


 

Related information

Time lapse video of a day on-board a research cruise

 

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