St Kilda Survey COR0924 (Blog #1): More than just muck
By Chloe Blackman
In our latest blog post, our offshore survey team is setting sail to the seas off St Kilda as part of the Defra-funded mNCEA (marine Natural Capital and Ecosystem Assessment) Programme. The team will be looking at the deep sea mud in the area, which is ‘more than just muck’ and digging into the true value of St Kilda’s muddy marine habitats.
Understanding the true value of our marine ecosystems is essential for driving conservation efforts. In the JNCC Marine Monitoring Team, we have been working tirelessly to fill information gaps in our marine evidence base. This has involved conducting surveys of offshore habitats through the mNCEA initiative – 'm' referring to the marine branch of the Defra-funded Natural Capital and Ecosystem Assessment (NCEA) Programme.
The project is driving data collection efforts on the UK's land and water ecosystems, assessing their condition, changes over time, and the benefits they provide to society. As part of this work, together with colleagues from the Agri-Food and Biosciences Institute (AFBI), we are busy preparing for one last offshore survey of 2024 before the onset of winter. We are setting sail for the seas off St Kilda, aboard AFBI’s research vessel Corystes, aiming to implement an ambitious data collection plan.
Protecting our 'natural capital'
The societal benefits provided by natural habitats can be thought of as assets, or 'natural capital', in our environmental bank. Gathering high-quality data from offshore habitats enables us to assess our natural capital and subsequently make informed, sustainable management decisions.
Although they might seem distant from our daily lives, healthy offshore marine habitats hold immense value for everyone. They support vital food production as nursery grounds for commercially harvested species, aid in climate regulation through carbon sequestration (capturing and storing away carbon dioxide from our atmosphere), play crucial roles in the cycling of nutrients, and harbour rich biodiversity. When these habitats are degraded by human activity, for example by overfishing, their ecosystem services become compromised, with negative impacts for people and the planet. By safeguarding our natural capital, we ensure it does not depreciate in value, preserving crucial ecosystem services into the future.
The biodiversity of St Kilda’s seas
The St Kilda Archipelago – a cluster of four main islands (Hirta, Dun, Soay and Boreray), along with several smaller islets and sea stacks – forms the farthest western reach of the Outer Hebrides. Perched close to the edge of the continental shelf, the seabed slopes down steeply to the north and west of the Archipelago. Here, nutrient-rich waters well up from the depths of the Rockall Trough, fuelling plankton production which sustains a thriving marine food web. Furthermore, the array of benthic (seabed) habitats in the area, including rocky reefs, sandy plains and muddy expanses, provides a range of ecological niches, or 'roles' to be fulfilled by different species. Together, the plentiful food and varied habitat of St Kilda's seas promote rich biodiversity. Recognised as nationally important, the benthic habitats located on the shelf edge to the north-west of St Kilda are classified as a Nature Conservation Marine Protected Area (MPA) – the Geikie Slide and Hebridean Slope MPA. Furthermore, 3,995 km2 of the waters surrounding St Kilda have been designated as a Special Protection Area (SPA), serving to safeguard seabird foraging areas and prey – the Seas off St Kilda SPA. Indeed, several iconic species of seabird exploit these waters for their abundant fish populations, including gannets, fulmars and puffins. Sightings of iconic marine mammals, such as whales, dolphins, and seals are also commonplace, and we hope to see them whilst out on survey!
The overall aim of this survey is to collect comprehensive biological and environmental data from marine habitats off St Kilda. Sampling will take place predominantly outside of existing protected areas, south of the Archipelago, where there is the greatest deficit of information, with a particular focus on offshore deep-sea mud habitat.
Why we should value 'deep-sea mud'
'Deep-sea mud' may not sound particularly glamourous; however, these muddy expanses represent important ecological assets. In fact, when undisturbed they can be biodiversity hotspots, hosting alien-like assemblages of delicate sea pens (a type of soft coral bearing resemblance to a feather quill) and burrowing megafauna (typically including the charismatic Norwegian lobster – Nephrops norvegicus). Yet, these ecologically important communities are vulnerable to human pressures, and, once degraded, have limited recovery potential. Offshore mud habitats are often subject to high levels of disturbance from human activity, particularly from trawl fisheries. Ultimately, closing information gaps on their condition as well as the extent of any physical disturbance is imperative to informing sustainable management.
Image 1: Map showing the different habitat types within the planned area, and the overlap with the Seas off St Kilda Special Protection Area (SPA).
What survey techniques will we use?
We want to know how St Kilda’s seabed habitats are being impacted by fishing pressure. Therefore, we plan to sample from sites which experience different amounts of fishing activity. So that we can assess their natural, undisturbed state – or 'reference condition' – we will principally target sites which are not heavily fished. Data collection will be carried out primarily using two conventional survey techniques:
- Grab sampling:
- We will deploy a ‘Day Grab’ – apparatus which samples a fixed volume of sediment from the seafloor.
- Once back on board, we can analyse the type and amount of infaunal (burrowing) species within the samples.
- We can also perform Particle Size Analysis (PSA) which looks at the size range of sediment particles which make up the sample. This helps us to characterise the habitat and is closely linked to the types of species which we would expect to find living there.
- Seabed imagery:
- We plan to use a sledge camera to obtain high resolution still images and videos of the seabed.
- By analysing the imagery, we can assess the type and relative abundance of species which live on the seafloor, inhabiting the site, with particular focus on the extent of ecologically important sea pen and burrowing megafauna communities.
- From this imagery, we can also evaluate impacts of human activity on the seabed, for example the physical impact of bottom trawling which can be recognised from furrows created by heavy trawl gear.
Environmental parameters, including depth, temperature and salinity, will be recorded from associated sampling stations.
Alongside these tried and tested techniques, we will be trialling two novel methods for marine biodiversity data gathering. Firstly, we will be testing the use of Baited Remote Underwater Video Systems (BRUVS) across various seabed habitats and in the pelagic environment, aiming to evaluate their effectiveness in different contexts. BRUVS are underwater cameras which are baited to attract and record marine life, providing valuable insights into species presence and behaviour without the need for direct sampling.
Image 2: Baited Remote Underwater Video System (BRUVS) to be used during the St Kilda survey.
Additionally, we aim to test the use of 3D-printed environmental DNA (eDNA) metaprobes (Image 3), deployed on our sledge camera. eDNA metaprobes collect genetic material which has been shed by marine organisms into their environment, offering a non-invasive method to detect and identify species, even those not captured on video. If successful, the use of these tools will enhance our understanding of the marine biodiversity inhabiting St Kilda’s seas, informing more comprehensive data collection techniques for future surveys.
Image 3: 3D-printed environmental DNA (eDNA) metaprobes
The mNCEA St Kilda Survey (COR0924) will run from 26 September until 11 October. Be sure to keep an eye on our Blog Feed and social media – Facebook, LinkedIn, and X (Twitter) – for updates.