Tegnue

Tegnues are rock formations which have developed in the sea bottom of the Gulf of Venice, in the northern Adriatic Sea. They are bio-sediments which are very similar to coral reefs and for this reason they are called Adriatic coral reefs. They are found especially off the coass of thee inlets of the Lagoon of Venice: Lido, Malamocco and Chioggia, where there are four such formations. They are called Serenissima, San Marco, Lido and Pellestrina. They are at a depth of -15/-40 m. The largest formation is off the coast of the Chioggia inlet.

Etymology

Tegnue is a Venetian dialect word which means "held back." The name was given by fishermen whose nets got caught in these rocks at the bottom of the sea, which held them back.

Morphology

Tengue are clastic sedimentary rocks. They are carbonite rock formed by marine organism superimposed on hard substrates which had previously formed though the consolidation of sands. They are reefs which are different from tropical reefs in that the main bio-constructor organism is not coral, but Corallinaceae, red calcareous algae. Both vegetable and animal organisms have contributed to their formation. The hardening of the sand incorporated calcareous shells of molluscs which stratify to form a certain thickness.

These coralline formations are an anomaly compared to the dendritic bottom of sand and loam on which they rest. To improve the understanding of these formations researchers carried out more than 200 dives to map the morphology and bathymetry of the sea bottom on which they rest, took samples of loose rocks and sediments and placed wells to analyse the water in the depths of the sea.

Previous genetic models were not satisfactory, so the samples were analysed in a laboratory. This has shown that the tegnue developed along elongated morphological structures of ancient fluvial channels present in the plain of the bottom of the sea which was emerged during the last glacial period some 20,000 years ago. The sediments have been dated to 9,000 years ago and their hardening on which the first organisms became attached occurred 7,000 years ago.

Fish Oasis

These rocks are a habitat for many species of fish and crustaceans, including: European congers (conger conger), red scorpionfish (Scorpaena scrofa), brown meagres (Sciaena umbra) , Mediterranean chromis (chromis chromis) , brown combera (Serranus hepatus) and various species of combtooth blennies (Blenniidae). There are also sponges, sea squirts and sea anemones.

Protected area

In 2002 the tegnue were declared and environmental protection area where fishing is banned by the Ministry of Agricultural and Forestry Policies. This was promoted by Chioggia's council, universities in Veneto, the Port of Venice Authority and the fishermen and tourism associations.

Tegnue Aquarium

A reconstruction of this habitat can be seen at the Natural History Museum of Venice. It is called Acquario delle Tegnùe (Tegnue Aquarium). This museum has released a short video clip about a majid crab in the aquarium. It has also published, in conjunction with the Regional Agency for of the Preservation and Protection of the Environment of the Veneto, a long and detailed publication called Le Tegnue, ambiente, Organismi e curiosità (Le Tegnue, Environment, Organisms and Curiosities).

These links provide photos of the environment and fauna the tegnue: More photos can be found in this link:

A bibliography of academic atricles about the tegnue can be found in this link:

See also

• Adriatic Sea
• Lagoon of Venice

Category:Venetian Lagoon Category:Geography of Venice Category:Chioggia Category:Bays of Italy Category:Bays of the Adriatic Sea