Garda Stack in located off of the SE corner of the island of Vailia. Garda Stack is one of several stacks and shallow rocky reefs in this area, creating a complex underwater topography. My favourite dive at Garda stack is through the first east-west facing arch and a circumnavigation of the north most leg. The dive offers a great diversity of life in a variety of vibrant colours.
The south leg of the arch joins a rocky reef stretching out to the east, providing a degree of shelter from the predominantly south-westerly swell. This area is however one of the places in Shetland where there is a noticeable amount of tidal flow, and although the arches can be dived at most states of the tide the channelling effect of the narrow arch and shallow water means that there can be quite a flow of water. Although as a boat dive this shouldn’t pose a particular problem, it can making trying to stay in one spot a little tricky.
I have always started the dive on the east side of the arch, sheltering in the lea of the rocky reef. The underwater topography in front of the arch forms a basin down to 15m, with the rocky reef to the south and the entrance and legs of the arch shallowing to 10m. The bottom of the basin is sand with rocky outcrops and is relatively sparse in life but the walls of the basin are covered in large patches of Dahlia anemones in a fantastic variety of colours. With nudibranchs, deadmans fingers and colonial sea squirts adorning the rock walls of the basin it easy to forget that it is the arch which is the main part of the dive. Entering the arch the marine life is typical of current swept habitats; deadmans fingers, jewel anemones, hydroids and sponges cover every available surface. Amongst these sedentary animals, nudibranchs such as the crystal seaslug (left), decorator crabs, scorpion fish and skeleton shrimps can be found clinging on and feeding in the current. I always think that skeleton shrimps have an ‘Aliens’ like appearance, and can be found in great densities on sponges and dead man’s fingers.
At the arch exit there is a number of options to turn south, towards yet another arch, to turn north and circumnavigate the leg or to go back the same you’ve come. Circumnavigating the arch takes you shallower and into a kelp park. If there has been a lot of tide through the arch there will be tide here too. The kelp park has some of the largest stipes I have ever seen, like the trunks of small trees and if you haven’t planned the dive for slack they make useful holding on points! The kelp park is home to decorator and edible crabs and nudibranchs. The north-east corner of the arch leg is covered with anemones and is an impressive sight before returning to the start of the dive.