ABOVE: Video frame showing dead men's fingers growing around the exposed frames in the bow of the vessel.

ABOVE: Video frame showing sea fir's on the deck, while dead men's fingers preferentially colonise the more exposed coaming.

ABOVE: Video frame showing life beneath the stern, predominantly sea firs, but including tube worms and occasional urchins and dead mens fingers.

The immediate impression of a simple ecology, based on a two species mix of sea firs and dead men's fingers, with a few grazers and hanger's on is clearly over simplifying the picture. Micro-analysis (previous slide) indicates a complex and diverse ecology, with numerous types of sea-fir providing a living substrate for other organisms over a considerable part of the wreck.

Given that the actual ecology is very complex, there do, however, appear to be some gross variations in the mix which may reflect local changes in conditions. Sea-firs dominate many sheltered areas, such as the decks of the vessel. By contrast exposed structures, such as ribs in the bow area, are almost entirely covered by dead-men's fingers. (See photographs left).

To correlate biological distribution patterns and the extent of preservation we require a measure of the preservation. Unfortunately gross measurements are inconclusive. Large numbers of hull plates have been lost from the bow, but this may reflect damage cuased by impact with the shore as the ship was run aground.

One factor that we have noted, however, is that the most exposed areas of ironwork (coaming edges and so on) have tough, cohesive concretion coatings. By contrast the decks have no measureable concretion. We expect concretion to protect the underlying iron, by providing a barrier to the oxygen which causes corrosion.

At the Kinlochbervie site we hypothesised that the slow current regime there resulted in a lack of concretion. This is supported by our preliminary study on the Thesis. In this we have observed a correlation between exposure and concretion formation, with thickest concretion on the most exposed ironwork.

The deposition of concretions onto metals is known to reduce corrosion rates, and thick concretion layers are commonly encountered on iron artefacts more than one hundred years old. A failure to form a stable concretion layer, may, therefore, result in comparatively rapid dissolution of the metal over extended time periods.

It is well known that different species have different preferences for habitat types. On the Kinlochbervie site few of the species we would have expected to find on an exposed rocky sea bottom were present. On the Thesis we observe that soft corals dominated the most exposed areas of the wreck. Areas where the formation of concretion is also most advanced.