Underwater acoustic networks: the FP7 UAN project

The EU-funded project UAN - Underwater Acoustic Network aims at conceiving, developing and testing at sea an innovative and operational concept for integrating in a unique communication system submerged, surface and aerial sensors with the objective of protecting off-shore and coastline critical infrastructures. A crucial aspect of the project consisted in the use of autonomous underwater vehicles (AUVs) as mobile nodes in the underwater acoustic communication network. In particular, AUVs have the role of adapting the network geometry to the variation of the acoustic channel. This paper reports on the project concept and vision as well as on the progress of its various development phases. The recent at-sea successes that have been demonstrated within the UAN framework are detailed and results of the final UAN project demonstration, UAN11, held in the May of 2011, are reported. The UAN network was in operation for five continuous days with up to five nodes, of which three of them were mobile nodes. © IFAC.

Comparison of small remotely operated vehicles and diver-operated video of circalittoral benthos

Underwater video transect methods using small remotely operated vehicles (ROVs) and diveroperated video (DOV) are commonly used in benthic biodiversity assessments. Constraints posed by deeper waters have made surveys of the circalittoral zone ([30 m depth), a particularly challenging problem. Here we compare benthic diversity metrics and cluster analyses obtained with ROV and DOV between 45 and 65 m depth off southwest Iberia, across local (tens to hundreds of meters) and regional scales (tens of kilometers). Results showed no difference between methods in terms of the benthic species richness, taxonomic distinctness, and beta diversity, but only minor differences in the spatial structure depicted at the regional level. At the local scale, DOV performed better at discriminating patterns likely because of the divers visual acuity. We found that small ROV and DOV are reliable and comparable methods for the study of circalittoral benthic assemblages and can be used in a complimentary way to detect the greatest amount of variation in benthic ecosystems. Our study facilitates the understanding of capabilities and limitations of two underwater video methods and provides important insight into choice of the most appropriate technique.

Underwater survey of ichthyofauna of eastern Atlantic seamounts: Gettysburg and Ormond (Gorringe Bank)

Gettysburg and Ormond are seamounts belonging to the Gorringe Bank, which is located on the Europen-African plate boundary. Given the importance of these oceanic features for understanding marine biodiversity patterns, two surveys were carried out in 1998 (Gettysburg) and 1999 (Ormond) using diving, photography and video for species identification and abundance evaluation. Of the 9 fish species found at Gettysburg and 11 at Ormond, 6 were common to both sites and these included the dominant species: the oceanic and commercially important, Seriola rivoliana, and the coastal, typically Atlantic-Mediterranean Coris julis and Anthias anthias. The strong representation of coastal, demersal and Atlantic-Mediterranean species in the Gorringe Bank region and the presence of Abudefduf luridus, an endemic Macaronesian species, at Gettysburg suggests that the upper part of these seamounts may have acted and still act as “stepping stones” for the dispersal of coastal species.