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Two wrecks related to the Battle of Trafalgar (1805) were studied. Following the guidelines of the UNESCO-2001 Convention for the Protection of the Underwater Cultural Heritage, a holistic and interdisciplinary approach based on the development of four of the thirty-six Rules of this international agreement was applied. A non-destructive survey technique was developed to obtain information from the scattered cannons and anchors without altering their condition (Rule 4). The work performed provided information about the origin of both wrecks, the Fougueux and the Bucentaure, two ships of the line of the French Navy, and allowed to characterize the state of conservation at each site without jeopardizing their future conservation in the marine environment. In addition, measurements of the main physical, chemical and biological variables allowed correlating the conservation status at each site with the marine environmental conditions (Rule 15). Thus, in Fougueux shipwreck large iron objects are corroding at a higher rate (between 0.180 and 0.246mmpy) due to high sediment remobilization and transport induced by waves at this site, causing damage by direct mechanical effect on metallic material and by removing the layer of corrosion products developed on the artefacts. Meanwhile artillery on Bucentaure site, covered with thick layers of biological concretion, is well preserved, with lower corrosion rates (0.073 to 0.126mmpy), and archaeological information is guaranteed. Finally, the effectiveness of the cathodic protection as a temporary measure for in situ conservation (Rule 1) was evaluated on a cannon. The use of a sacrificial anode after 9months reduced the average corrosion rate (from 0.103 to 0.064mmpy) and the percent of corrosion rate in 37.9%. These results are very useful for developing a decision making system of the Site Management Program, based on predictive models of artefacts permanence and risk factors in the marine environment (Rule 25).

Fouling communities on artificial marine structures are generally different from benthic communities in natural rocky habitats. However, they may also differ among different types of artificial structures. Two artificial structures in direct contact with arriving vessels were compared: floating pontoons within recreational marinas, and sea-walls within commercial harbours. Natural rocky habitats were used as a reference, and the genus Eudendrium (Cnidaria, Hydrozoa) was chosen as a bioindicator. The assemblages were different among the three types of habitat studied, with different species characterising each habitat. The probability of finding an invasive Eudendrium species was significantly higher on pontoons. Diversity was the lowest on pontoons, but it was not significantly different between sea-walls and natural rocks. In general, a barrier to the spread of exotic species exists between harbours and natural rocky habitats. Floating pontoons seem to be a less suitable habitat for native fauna and a key element in marine biological invasions.