This article , written by Georgina Jones, was first published in African Diver, and is republished here with their kind permission.
Nudibranchs of Pietermaritzburg
The SAS Pietermaritzburg (predictably always referred to as the PMB) was scuttled in 22m of water close to Millers Point in False Bay in 1994. It was an unusual end to an unusual surface career. The PMB was previously the HMS Pelorus, a minesweeper, and was the lead ship in the invasion of Normandy at D-Day in the Second World War, clearing the way for the Allied invasion fleet.
The HMS Pelorus, an Algerine class minesweeper, was launched in the Scotland in 1943. The Algerine class was designed for multi-purpose use, incorporating the lessons learned during the long war. They were large enough to accommodate equipment for detecting contact, acoustic and magnetic mines and as well as for detecting submarines. The Pelorus was, most appropriately, named after a dolphin called Pelorus Jack, which was famous for guiding ships through a dangerous sea passage off the New Zealand coast between 1888 and 1912. Like the dolphin before it, the Pelorus was mainly involved in convoy duty, but in the cold waters of the north Atlantic. Its moment of glory came as the lead ship of the Normandy D-Day invasion in 1944. For eleven days, the Pelorus and other minesweepers kept the aproaches to the beaches clear of mines, despite heavy daily shellfire from onshore gun batteries and nightly bombing by Luftwaffe planes. When helping clear the harbour at Cherbourg, the Pelorus was struck by a mine which lifted the ship right out of the water. There were no human casualties, but the ship had to spend three months under repair. No doubt Pelorus Jack, which survived an attempted shooting in 1904, would have approved. Though other ships of the Algerine class continued with minesweeping duties well after the war, the Pelorus was sold to the South African Navy in 1947 and renamed the HMSAS Pietermaritzburg. As the Pietermaritzburg, the ship was used rather more mundanely as a training vessel and minesweeper. It was decommissioned for the final time in 1964 and then used as accommodations for the Mine Countermeasures squadron from 1968 to 1991.
After some debate as to its possible future as a maritime museum, the Pietermaritzburg was scuttled by explosives in late 1994 to form an artificial reef. The wreck initially lay upright on the sand, and was used for extensive penetrations. There has been one fatality one the wreck: a commercial diver on a training course, who, along with his buddies, got lost inside the ship. They ended up in a cabin and all managed to escape via a porthole apart from one man, who was too big to get out and drowned there. A very sobering testament to the perils of treating overhead environments with anything less than utter respect.
Fifteen years underwater off the Cape of Storms have left their mark on the PMB. It has been seriously damaged by winter storms — the most notable being the storm of late August 2008, which twisted the deck out of true and left the ship with a distinct list. Further damage was done by the storm of June 2009, which ripped the bridge off the ship. It can now be seen lying alongside the main wreck. There are still possible penetrations which can be done, but the ship plating is rather fragile in places and looks unstable, so the smart money is on staying outside the wreck.
Not that staying outside the wreck is a chore. As well as being able to marvel at the changes the Cape seas have wrought, as an artificial reef, the PMB has few equals. The wreck is covered with all manner of marine animals, from sea fans to urchins and mussels. Seacatfish lurk in crannies and toadfish and blennies peer out from their hiding places. And for those who know where to look, the PMB is a nudibranch heaven. On an average dive, eight different species of nudibranch can be spotted, and occasionally, more than ten.
Warty pleurobranchs (Pleurobranchaea bubala) creep over the sand in search of other sea slugs to devour. Sand slugs (Philine aperta) burrow though the rich sediment in search of their prey of small molluscs and worms. These slugs fear few predators because they secrete sulphuric acid as a defence. On the wreck itself, gas flame nudibranchs (Janolus nakaza) light up dark corners. Two visually indistinguishable species of silvertip nudibranchs (Janolus capensis and Janolus longidentatus) are often seen. These two species have numerous physical differences when investigated under a microscope. To divers, however, the Cape silvertip and the medallion silvertip are only distinguishable by their egg ribbons, one being globular with many small eggs and the other being a flat medallion shape with fewer eggs.
Bright orange egg rosettes alert divers to the presence of the black nudibranch (Tambja capensis), a gorgeous animal with a bright turquoise stripe running along its body margin. Crowned nudibranchs (Polycera capensis) graze on fernlike moss animals. Purple ladies (Flabellina funeka) and white-edged nudibranchs (Flabellina capensis) hide among the fronds of their hydroid prey while orange-eyed nudis (Cratena capensis) flash their warning spots and candy nudis (Cuthona speciosa) dazzle the eyes — or would if they were any bigger. As it is, the longest is only 2cm in total length, but that makes them an even more exciting species to spot.
Perhaps being the host to a menagerie of extraordinary creatures is a fitting end for the namesake of an extraordinary dolphin.
Algerine class minesweeper
keel laid down: 8 October 1942 at Lobnitz and Co. Renfrew, Scotland
launched: 18 June 1943
completed: 7 October 1943
Displacement: 1330 tonnes fully loaded,
Length over all: 68.6m.
Maximum speed: 16 knots,
Powered by: two 3-drum boilers supplying two 4-cylinder triple expansion steam engines and twin screws.
Indicated power: 2400Hp.
Range: 5500miles at 10 knots.
Crew: 115 men.
Armament : 2 x 4” guns, 2 x 40mm guns, and 4 depth charge launchers.