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MERP Fieldwork

MERP fieldwork was a crucial part of the programme; with both large and small research ships working along the length of the British Isles. Though the aims of the individual research cruises were varied and specific, they all strived to supply knowledge on potentially important pelagic and seabed processes. Computer simulations of the ecosystem suggest that these particular processes could be important overall, however they have not been added to models due to lack of understanding and data.

The scientists undertook MERP fieldwork to find answers to the following key questions:

Does seaweed fuel offshore food webs?

What is the contribution of inshore seaweed to the food web further offshore?

Fronds from undersea kelp forests are abraded and washed up in rafts onto the tideline. These are a familiar sight, but how much finds its way offshore to feed the commercially valuable inshore food webs?

This autumn MERP scientists have been running transects from the kelp beds to 20 km offshore from the West coast of Scotland, the east coast of Northern Ireland, off Anglesey and off Plymouth. Sampling has been undertaken of the water column and the seabed food web at increasing distances offshore to gain understanding of what proportion of the fuel at the base of the food chains originates from seaweed and what comes from phytoplankton (the microscopic suspended in the water which support the offshore food chains). The method used will be stable isotopic analysis where the different “signals” of these contrasting food sources will be measured from the natural abundances of the rare heavy isotopes of carbon and nitrogen.



Is the seabed a permanent sink for seaweed carbon?

How do the above two types of food sources floating in the water column get incorporated into the sediment, and how does that signal change through the seasons of the year?

This work adds detail on the broader approach above, giving it temporal resolution, identifying key pathways though which the seabed benefits from these food sources, and providing an understanding on whether the carbon in those food sources ends up “locked up” in the sediment habitat, or whether it is recycled and lost again to the water column. This later part is crucial to understand whether the important role played by seaweeds in taking CO2 from the water (and therefore increasing the ability of the ocean to absorb more CO2 from the atmosphere) indeed promotes a permanent sequestration of CO2 from the atmosphere, or whether it is just a seasonal, temporary process.

For this, MERP scientists have been running R.V Plymouth Quest cruises every 8-10 weeks to the reference site known as 'L4', 15 km SW of Plymouth. Here scientists have been using corers to get field data, and bringing sediment cores to the lab where we use different techniques, including stable isotopes for carbon and nitrogen. Key pathways investigated are: feeding processes (from the species filtering what is in the water column as food, to those eating them, small and large); bioturbation (the way in which animals burrowing in the sediment may bury fresh food like seaweed debris and plankton settling on the sediment surface and therefore make it available to deeper burrowing animals); and bioirrigation (the flushing of the sediment by burrowing animals, which may lead to a new release of the carbon that was once eaten (as seaweed and plankton) back to the water column.



Does size dictate the pace of life?

Various sizes of monkfish on deck of boat
How far can the simple trait of body size explain the large-scale patterns that we see in the sea?

Computer models need simplification to manage the complexity in real food webs. Body size has a large part in dictating the pace of most ecological processes, so MERP scientists have been completing a variety of cruises to better quantify the “biomass spectrum” in the water column and at the seabed. At a large spatial scale the Cefas (Centre for Environment, Fisheries and Aquaculture Science) Endeavour and Prince Madog (Bangor University) research vessels have been working this autumn in the western English Channel to monitor everything from microbes to whales. The dynamics are highly seasonal so this has been covered at Plymouth Marine Laboratory's reference time series site, 'L4' with 6 weekly night time mini-cruises that started in February 2015 and will go on for another year.



Do jellyfish bend the rules of ecology?

How do variations in body form affect these broad-brush, size-based depictions of food webs?

Jellyfish may appear large but over 99% is water and only a tiny fraction is carbon. This makes it difficult to determine what measure should “size” really be based on. Jellyfish are important ecologically and some reports suggest that they are increasing, possibly as a consequence of human activities. MERP scientists have been sampling them seasonally and regionally as part of the size spectrum based on length or carbon mass, to better understand their ecological role. For this the team have been using novel molecular methods to better understand their feeding, in particular whether they eat or compete with the larvae of commercially important fish.