They collected undisturbed samples of sediment and supernatant water using a multi corer at 8 locations on the south and east of the island. One core from each location was then transferred back to shore where the research team could perform eDNA testing.
The project also looked at how protection from trawling and dredging activities might affect the capacity of the seabed to accumulate and store organic carbon. Researchers want to understand how this protection affects the biodiversity of seabed habitats, as it is likely that the animals that live around Jersey may play an important role in the flux of carbon through these environments.
The CMS team collected cores both inside and outside of the Jersey Marine Protected Area where mobile fishing gear is prohibited to enable comparisons in seabed organic carbon content and biodiversity according to different levels of seabed disturbance.
IN-FIELD TECHNIQUES
Various techniques were used to measure differences in biodiversity: Baited Remote Underwater Video Systems (BRUVS) were deployed to collect information on the abundance and body size of different fish and highly mobile invertebrate species such as crabs or lobsters; ROV and photo- quadrants were used to quantify the density and species diversity of less mobile animals living on-top of the seabed, these include sponges, ascidians and hydrozoans; sediment grabs were used for counting the biodiversity of animals living within the sediment itself.
CMS GeoScience worked with the Convex team to design this survey. With more interest in the top layers of sediment, it was decided that the HPC corer would be deployed in 3 m mode, with a smaller corer aiming to help mitigate some of the tidal restrictions. After consultation, the project scope was defined as 55 vibrocores, predominantly around the south and east of the island.
OPERATIONAL CHALLENGES
Each location was assessed and categorized depending on whether they were exposed to weather or tidally restrained. Weather forecasts were changeable and so it was vital that the team acquired the more weather sensitive sites, with contingency plans in place for operations to go ahead depending on the observed sea conditions at the time.
The local geology also presented specific challenges, with rocky outcrops being exposed by the high tidal range. Extensive planning using tidal and weather forecasts, as well as water depths, enabled the team to maximize working windows, while the choice of a smaller, more compact vessel helped operators safely navigate busy waters.
Cores recovered deposits ranging from silty sands to coarse gravels— igneous bedrock in many cases. The cores had to remain at a constant temperature of between 4–5 degrees, which was made more difficult as many of the locations were >4-hour steam away from harbor, so an onboard chilling facility was required.
Speaking exclusively to ON&T, Mechanical Design Engineer, Jack Foll, said of the unique campaign challenges:
“We knew we would be working within a demanding environment. The waters in which the team were deployed experiences a tidal height of up to 12 m, and this meant that our HPC corer had to operate in 3 m to compensate for the strength of the tide. The unseasonably inclement weather throughout our time on the island meant the team had to work within tight windows of opportunity, adding even more to the complexity of the project.”
This story was originally featured in ON&T Magazine’s September 2024 issue. Click here to read more.
