THE FRIGATE HMS SCYLLA has now been on the seabed in Whitsand Bay near Plymouth since late March 2004.
During this five-year period, recreational divers have reported their observations and submitted images to biologists, helping to prepare a full account of marine-life colonisation.
More than 240 species have now been recorded on the wreck. Highlights were the very rapid settlement of barnacles, tubeworms, tubular sea firs and large solitary sea squirts. Unexpectedly, there was also a massive settlement of green sea urchins and queen scallops early on.
Mussels colonised in the first summer, but were quickly despatched when common starfish settled and found them. By the end of the first year, a "classic" wreck species, the plumose anemone, was expanding its population.
In the second year, Devonshire cup corals and white dead men's fingers turned up. But fish, probably wrasse, had "found" the sea urchins, and they were changed into shell middens.
By the third year, the colonisers of the reef were beginning to look like a mature wreck community, especially with the expansion and growth in size of characteristic species such as the plumose anemones and dead men's fingers, as well as the presence of predominantly foliose rather than filamentous seaweeds.
Although expected populations of territorial wrasse are still not up to the numbers that can be seen on the nearby James Eagan Layne wreck and there are doubtless changes still to come, Scylla is now full of colourful, attractive and photogenic species.
WHAT CAN YOU SEE WHERE?
On the shallowest part of the reef are kelp plants and, in spring and summer, dense foliose algae. Once the seaweeds are established each year, rock cook are present. Pollack occupy the bridge, and are found everywhere on the outside of the reef.
Look out into the surrounding water and you may also see shoals of scad, bass and mullet - even a sunfish has been reported. However, come winter, the area looks far more barren, as the seaweeds die back.
The bow, like the rest of the reef, was rapidly colonised by tubeworms and barnacles. These were, in turn, consumed by urchins and starfish in the first autumn. The green sea urchins, normally seen only in the South-west under boulders on the shore, arrived in great numbers on Scylla.
If you looked more closely at the bow that autumn you would see the first of the plumose anemones that would soon dominate the vessel visually.
Dead men's fingers were slower and, although they settled in 2005, were obvious only by late 2006.
Look a bit more closely to see colourful elegant sea anemones. The different varieties are rose-coloured, white, mottled brown and orange, and a fantastic subject for macro photography.
The fore and aft decks in particular demonstrate major seasonal changes.
In spring and summer, expect a meadow of foliose algae with dense antenna hydroids.
Come the winter, the appearance is much more bare. Sweep away the slight layer of silt and beneath it you will see grey paint, parchment tubeworms and scattered calcareous tubeworms, perhaps with thousands of tiny snails.
Remarkably, sea-fans have settled and survived well in parts of the foredeck.
By the end of 2008 they were beginning to branch - but were no more than 10cm tall.
Travel along the walkways and you will see much of what is on the outside. This is where you can spot the small number of territorial fish (wrasse and tompot blennies especially) that had colonised the reef by the end of 2008.
The roof of the walkways is where mussels survived until the last succumbed to the common starfish. It is now colonised by plumose anemones and solitary sea squirts.
Whatever lives there has to be able to survive the trapped exhaled air of passing divers.
The afterdeck includes the grid of metal that was the helicopter deck. Featherstars have found a footing there and are abundant.
The holes are occupied especially by solitary sea squirts and, come the spring, foliose red algae will be abundant.
Ross "coral" settled on Scylla in its second year and grew rapidly. The potato crisp-like colonies are extremely fragile, and seem to me to be mainly restricted to vertical surfaces or in among protruding metal, but were up to about 20cm across by the end of 2008.
Look around the outside of the helicopter hangar to see a late (well, 2006) but now prolific coloniser, the orange pumice-stone bryozoan.
Under the stern, the effectiveness of anti-fouling paint is starkly obvious.
The white paint with a mottled red appearance is bare except for where it has flaked away, leaving a less toxic surface to be colonised by oases of tubular hydroids, sea squirts, barnacles and tube-dwelling amphipod shrimps.
Look around - can you see anything at all daring to crawl over the anti-fouling paint? But the rudders and the propeller-shaft are well-colonised, and a brown crab has found a lair at the pinion of one of the rudders.
Poor cod found Scylla almost immediately, and the expected striped bib are now present, but not in the numbers on many nearby wrecks.
Inside the swim-throughs, there remains a great deal of uncolonised surface. Solitary sea squirts and plumose anemones are the most conspicuous species, but you may see featherduster worms and, especially along struts or wires, featherstars.
The odd conger eel has been recorded, but the reef is not a "conger wreck".
In general, and providing that you keep to the swim-throughs, the reef has little silt. However, if you look in the corners, you may find thick pockets of mud colonised by burrowing anemones.
Look upwards to see large numbers of prawns, the occasional squat lobster and, perhaps, tompot blennies.
The major "snags" have been removed from swim-throughs, but there are still some sticky-out bits that might be good "structural complexity" for marine life but hazards for you.
On the sides, the reef has become densely colonised with colourful "elegant" sea anemones, jewel anemones, plumose anemones, dead men's fingers, large solitary sea squirts, star sea squirts, orange pumice stone bryozoans and much else. The effectiveness of the anti-fouling paint is again very apparent.
The lower plating is where bored divers leave their messages of love and despair written into the silty coating over the hull. Who are Rob and Di, and will they return to Scylla with
a new appreciation of the fantastic marine life that now populates the reef?
THE FUTURE
Species on Scylla for the long term include the tubular and antenna hydroids, plumose anemones, the dead men's fingers and the sea fans. The high number of solitary sea squirts is unusual. They live for up to about five years, so might substantially disappear, but newly settled individuals have been seen in some years after 2004.
Steel wrecks out of Plymouth are substantially dominated by barnacles or, on rusty steel, nothing, and that might eventually be the fate of Scylla.
Other changes are likely. Especially if the common starfish do not survive in high numbers, there may be settlements of mussels, as has occurred on the James Eagan Layne at times.
Common sea urchins are still a rarity and the black sea cucumbers common on wrecks have not been seen yet.
Some features attractive for their marine life, such as the safety nets by the helicopter deck, have already gone, but what's left is pretty robust. We hope that the numbers of territorial fish, especially wrasse, will pick up. Whatever the future holds for Scylla, the reef is fascinating for divers, especially those interested in marine life and photography.
Scylla was placed on the seabed in Whitsand Bay on 27 March 2004 by the National Marine Aquarium, with funding from the South-West of England Regional Development Agency. You can call up a PowerPoint presentation of marine life on Scylla from www.marlin.ac.uk/scylla. If you see any species on Scylla that you believe should be recorded to carry on the story of colonisation, go to www.marlin.ac.uk/rml. A detailed account of colonisation on Scylla is being prepared for publication with Sally Sharrock of Seasearch.
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