Even the gloomy, grey December skys couldn’t damp the enthusiasm of Orkney Team Seasearch. The plan was to survey the marine wildlife inhabiting the Coln, the most intact of the cruisers remaining from the scuttled High Seas Fleet. The ship now lies on its starboard side at an angle of 90 degrees, in 35m depth of water in the middle of Scapa Flow and is a rich habitat teeming with life.
Seasearcher and Heriot Watt University Lecturer Jo Porter recounds the dive.
Descending the shotline, the first thing that comes into view is the port side of the vessel. Divers over the years have worn away much of the delicate life in the heavy traffic areas but it is a short hop to a more pristine territory just off the beaten track. Where the side of the ship starts to slope away gently down to the seabed, a rich and colourful turf of hydroid colonies, feather stars, sponges and cup corals have made their home.
Following along a small raised ridge running along the length of the hull we found the bright orange golf ball sized Suberites sponges dotted amongst the turf. They alternate between two distinct forms: sometimes they forming a compact ball with an obvious hole in the top, othertimes developing into a more extensive crust with several holes (osculae) through which they can filter the water to collect particles of food.
Solitary cup corals are abundant, sometimes solitary, sometimes in groups. They posses delicate transparent tentacles in a hard exterior that bizarrely looks not dissimilar to a horse’s molar. Taking a closer look, each of the tentacles ends in a small white knob; this contains specialised stinging cells that the coral uses to paralyse prey that stray too close. Small crustaceans are caught in the tentacles and then passed to the slit like mouth at the centre of the tentacles, where they can be passed into the stomach cavity. Once digestion has taken place any undigested materials are released back to the outside world via the mouth. These simple animals have just the one body cavity that they use for both taking in food and getting rid of waste.
In amongst the turf community there are patches where sediment has gathered. Here the small pinky coloured brittlestar with white spots, Ophiura albida, can be seen gliding across the surface and browsing as it travels. More obviously mobile species such as the hermit crab Pagurus prideaux scavenge around looking for morsels of food. The hermit crab is often accompanied by its symbiotic cloak anemone Adamsia carciniopados, which makes use of any scraps of food that the crab itself does not eat. The anemone is distinctive pale pinky-cream colour, with lurid purple mottled spots. It has its own special method for defending itself: if attacked it releases a series of very fine purple threads from inside its body cavity through slits in its body wall. These mesenterial filaments are coated with stinging cells and are used to deter potential attackers.
Larger predatory animals of the turf community include the brightly coloured Sunstar Crossaster papposus. Sometimes these animals can be seen arching the centre of their disk into a dome shape. This means that they are in the process of enveloping and slowly digesting away whatever prey they have engulfed. This may include smaller starfishes or bivalve molluscs. It is a slow process but once it has started there is little chance of escape for the prey.
Moving further astern we came across the blasted area around the engine room. Dropping down to 25m depth, a section of the wreck that has been blasted to reveals the innards, comes into view. Using a torch to peer inside the darker, overhanging areas of wreckage reveals shoals of small gadoid (cod like) fish taking refuge amongst the remains of the engine room. Here in a quiet corner, a solitary Wolf fish Anarhichas lupus has taken up a temporary residence. The body of the fish may be hidden from view in a crevice of the wreckage, but the fearsome toothy grin of this fish may give a fright to the unsuspecting diver!
The walls and roof of the ships innards are coated with a thick white fir of Moon jellyfish polyps Aurelia aurita Periodically the baby jellyfish are released out into the open water to complete the next stage of their life cycle. The presence of the divers’ bubbles in this area attracts swimming Guillemots to come down and have a look around at what is going on. Fascinating and agile underwater, these birds are beautiful to watch as they circle around.
Starting to head back towards the shotline, the edge of the deck provides a picturesque scene with some well-developed colonies of the branching Haliclona. Metal struts branching out from the deck edge are colonised by intensely coloured orange-red plumose anemones. Some have their tentacles out and feeding in feathery crowns whilst others are contracted back into jelly like blobs. Amongst the anemones are the striped skinny arms of many feather stars, stretching out into the water to capture food and pass it down to their mouths. They hang onto the struts with their claw like cirri, but if they get dislodged they can use their arms to swim through the water and find another suitable spot to settle back down. On the deck itself there is hardly a bare patch to be seen with so many crusts of sponges, carpets of sea squirts and patches of sea mats coating the surface.
Coming back to the shotline it’s a shame to leave when there is so much more to explore on this fascinating wreck.
- Bob Anderson
- Liam Thornes
- Jenni Kakkonen
- Joanne Porter
- Richard Shucksmith
- Rachel Shucksmith
- Amy Cromarty
- Ivan Houston
- Anne Bignall
- Georgia Connolly
- Andrew Want.