ONE BUOY, and then the second bobbed up on the shot. Hugging my camera to me to protect the dome, and stop the flashguns bashing me in the face, I rolled backwards off the tubes, finned rapidly to the line and started pulling my way down.
I cursed my computer’s heart monitor, which was beeping at me for exerting myself – too hi-tech for its own good. What did it want me to do – let go and drift with the comb and moon jellies floating past?
Still, if it was running a bit now, with luck we had timed it right for slack on the bottom. We reached the shot at 33m (and perfect slack) and, as the JIBS chart had shown earlier, a channel next to it leading to the pinnacle edge.
I returned Jen’s OK signal, and we started making our way down the steep-sided gully. A forest of fuzzy peach and white dead men’s fingers (Alyconium digitatum) covered the bedrock walls, striped anemones (Actinothoe sphyrodeata) continuing the colour theme.
Hornwrack bryozoan (Flustra foliacea) and oaten pipe hydroids (Tubularia indivisa) were dotted between, a sure sign that this spot was subject to some pretty extreme currents.
Then suddenly the gully ended, and we were faced with a sheer drop. Even in this 15m vis, I couldn’t see the cliff base, only the wall disappearing into the gloom below.
No current yet, so we were safe to drop over. Bearing our deco in mind, we gradually finned along the top of the wall in 34m, making notes on our slates as we went. My computer started beeping again, not happy at me for my heart rate, but I couldn’t help it, because before me was a photographer’s dream, and Jen and I were probably the first people to see it.
A sheer-sided vertical stack, separated from the main bedrock wall by a metre or so, protruded from the depths, its surface covered with bright white and orange plumose anemones (Metridium senile).
I made our modelling signal (hand behind the head, elbow raised) and Jen obliged, slowly swimming into shot to give some idea of the scale of the site.
SEVERAL PHOTOS LATER, and with a whisper of tide starting up, we began our ascent, and some well-earned nitrox for deco. Another successful survey dive on Shamrock Pinnacle was complete.
Imagine a chart of the seabed so detailed that you can see the shape of individual boulders, the smallest of gullies and the exact position of the best drop-offs – in fact, a wealth of potential dive sites.
This isn’t some far-fetched diving fantasy, it’s what the recent Joint Irish Bathymetric Survey (JIBS) project has achieved for a 3 nautical mile strip of coast off the north coast of Ireland, from Instrahull to Fair Head.
Current nautical charts of the area are based on lead-line soundings and sextant positions with guesstimates on seabed type based on whatever came up attached to dropped wax-based cylinders. Some of this information is more than 200 years old.
The lack of accurate data was a major headache for those trying to manage and conserve seabed habitats and archaeology, and the JIBS project provides much-needed information.
The survey used multi-beam sonar. Sonar provides depth information based on the time taken to return a beam pinged from the survey vessel to the seabed. The strength of the received signal (or backscatter data) gives an indication of the hardness of the substrate below and therefore the seabed type (such as sand or rock).
Older sonar methods could send out only a single beam, so obtained information only from a small strip of seabed with each pass of the survey vessel. As unsurveyed gaps are filled
by interpolation (or, as non-scientists call it, guessing) the final chart is not very accurate.
Multi-beam differs in that with each pass of the vessel, multiple beams of sonar are sent out, covering a much wider area and collecting data from many more points. The seabed can
be surveyed in far more detail for the same survey cost, although the EU-funded JIBS project still cost a not-inconsiderable 2.133 million euros.
The project has revealed the spectacular submerged geology of the north Irish coast in amazing detail: the horizontal resolution of the chart is 1m, and vertical resolution is an astonishing 1cm. Researchers from University of Ulster have identified 389 anomalies from the area (projections over 1m high), some of which could be previously unknown wrecks.
THE NEXT STAGE was to “groundtruth” the chart, testing for accuracy of the seabed prediction models, recording the species and habitats present, and flagging any sites of conservation importance. This was where we came in.
Diving previously unsurveyed reefs in great vis is a tough job, but someone has to do it, and it’s all part of my role as a marine biologist for National Museums Northern Ireland.
However, there was a serious purpose to this project. Bernard Picton (the museum’s Curator of Marine Invertebrates) and I had joined forces with Joe Breen, Head of Aquatic Sciences at Northern Ireland Environment Agency, and his team, to conduct a biological survey of rocky reefs in the area.
Our mission was to determine whether any of these were worthy of protection as a European Special Area of Conservation, or as part of the network of small sites to be proposed under the new UK Marine Bill, and to monitor reef sites in existing conservation areas.
The topographic information from JIBS enabled us to target specific features, such as walls and gullies, of known large sites such as Shamrock Pinnacle, whereas before survey sites would have been chosen using sounder and chart. More excitingly, it has revealed potential sites of interest in previously undived areas.
“I think that might be a sea cave.” Bernard was poring over the JIBS image of Bull Point, on the south tip of Rathlin Island. Joe’s eyes lit up. Submerged sea caves, a European protected feature, are a particular bugbear of his, as the exact number within Rathlin SAC is not known. The large cave and arch system at Ruecallan on the north wall is a highlight for any diver lucky enough to visit Rathlin, but the island’s limestone geology makes the presence of undiscovered caves likely.
Bernard remembers diving caves with the museum team in the 1980s on the north wall at a depth of 60m.
Tantalisingly this is just out of range for our work depth limit of 50m, and as accurate position-fixing technology was not available then, the exact locations are not known. Sure enough, on the JIBS image, a clear dip was visible on the smooth cliff – a data anomaly or cave? There was only one way to find out, and the next morning found us heading to Bull Point armed with GPS positions from the JIBS data.
The tide rips past here at up to 6 knots, creating standing waves at some parts of the cycle. Our trusty shot was deployed again. We had estimated slack to be around high water Belfast, so now we had to wait. Luckily, Steph had brought the hot Ribena and Hobnobs.
As predicted, around half an hour before high water the tide slackened, and Jen and I again found ourselves pulling our way down the line. We landed on a rather unprepossessing boulder slope – had the JIBS data been completely wrong?
Cursing sonar anomalies, I disappointedly pulled out my slate
and started recording: oaten pipe hydroid, more oaten pipe hydroid, bryozoan crust – this site was definitely bashed by the tide.
The vis wasn’t so good today, at around 7m, but as Jen and I worked our way east along the slope, I thought I could see something dark ahead. Probably just my imagination; back to the oaten pipe hydroid.
Seconds later, I was awakened from my hydroid-induced reverie by Jen’s torch flashing in my face. Expecting a seal at the least, I glanced up, only to see her swimming east, away from me.
Behind her, to my delight, was a 5m-high cliff. Swimming closer, I could see that it was pock-marked and grooved, typical limestone.
The surface of the rock was covered with a mosaic of brightly coloured sponges and sea squirts, in stark contrast to the barren, jagged, boulders we had just swum across.
AS WE ROUNDED THE CORNER, we could see that the face had parted from the main body of the cliff behind it, creating a small arch and, running down the length of the cliff, a mini-sea-cave. JIBS was right, and I made a mental note not to be so quick to doubt it.
A thread of limestone runs under the basalt of Rathlin Island, and this arch must have been created by the gradual erosion of this softer rock, a smaller version of its much-dived sibling on the North Wall.
Peering into a crevice in the limestone, I could see fluorescent yellow sponges covering its surface. If I wasn’t mistaken, this was a species we had recently described from Rathlin’s north wall, and not found anywhere since: Spongosorites calciola, named for its association with limestone substrates.
This was definitely a site to add to the potential protected list and, given the arch, there might well be caves somewhere near here. We would be back to look for them.
Having negotiated the Modiolus’s rather tricky dive-ladder, I reflected on the survey so far. Three weeks on Rathlin and a fortunate flat-calm spell had allowed us to record the marine life and habitats of sites from the island, ranging from the previously unstudied Bull Point limestone cliff to “Picton Reef” on the east coast, which we had found on a previous survey by using the boat’s echo-sounder.
JIBS has revealed this reef to be a substantial ridge, and has also shown the true extent of deepwater boulder slopes, with rare hydroids that we had known about from spot dives but in fact covered a wide extent of the east coast.
We had also surveyed several sites on Shamrock Pinnacle, six miles north-west of the island. Our detailed notes on the species and substrates would give Joe and his team enough information to protect at least some of them for future generations (including future divers). Next stop, the reefs off the Skerries…
The Joint Irish Bathymetric Survey Project was a partnership between the Maritime & Coastguard Agency (MCA) and Marine Institute of Ireland, co-ordinated by Northern Ireland Environment Agency, and funded under the European INTERREG IIIA Programme. Data analysis was undertaken by University of Ulster staff. More information and data from the project is available at www.marine.ie/ ome/services/surveys/seabed/JIBS.htm.
Seabed images were produced using the freeware Fledermaus iView4D software (available from www.ivs3d.com/ products/iview4d/).
The diving survey was part of the Nationally Important Marine Features Project, a partnership between Northern Ireland Environment Agency and National Museums Northern Ireland. Operator Aquaholics can arrange dives on the many reefs and wrecks of this area (www.aquaholics.org, 028 70832584).
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