ENTE
TUTELA
PESCA
DEL
FRIULI
VENEZIA
GIULIA
photo exhibi ti on
UNDERWATER LIFE OF THE NORTHERN ADRIATIC
“TREZZE” (beachrock outcrops)
photo exhibition
UNDERWATER LIFE OF THE
NORTHERN ADRIATIC
“TREZZE” (beachrock outcrops)
images by Luigi Paderni
at the
AQUARIUM OF THE FRESHWATER
SPECIES, ARIIS DI RIVIGNANO
(Udine, Italy)
opening 07 April 2011, h. 16:00
the exhibition will take place
from 07.04.2011
to 15.05.2011
Tu We Th Fr 09:00-12:00 & 14:00-17:00
Sa Su & holdays 10:00-13:00 & 15:00-19:00
closed on Mondays
i mages by Luigi Paderni
free entrance
TREZZE & TEGNÙE
THE ORIGIN OF NAME
The “trezze” (known by this name along the Friulian and the Giulian coasts), and the
“tegnùe” (more tipically Venetian), are submersed aggregates consisting of detritus and
organogenic matter, or of true rock, characteristic of the Northern Adriatic basin.
Both the “trezze” and the “tegnùe” are found over the arm of sea between Trieste and
Chioggia (trezze are especially concentrated between Trieste and Lignano), in form of
multiple and dispersed spots. Their extension can vary from a few to some thousands of
square meters, and elevation from the bottom surface can reach 1-4 meters (Mizzan, 1995;
Stefanon, 1966). They represent very special and unique environments (Bellot et al., 1998).
Among the flat and homogeneous Northern Adriatic seascape consisting of sandy and
muddy bottoms, these hard aggregates are natural reserve areas and natural nurseries for
the reproduction and settlement of species which otherwise could not be present in the
same zones. Many of these species are also commercially important, such as the European
clawed lobster (Scovacricchi 1998 & 1999; Scovacricchi & Burton, 1998), and the black
amber.
Anchors and fishing nets entangled in the “tegnùe“ or “tenùte” explain the name of these
submersed hard aggregates. Trapped nets and anchors in fact cannot be raised onboard
because they remain trapped, kept (in Italian they say they are “trattenute” or “tenùte”) by
the rocks and the other hard parts of these special marine formations. It is more difficult to
find out the etymon of the word “trezze”. Somebody think it derives from the Italian word
“trecce” (hair braids) following the romantic idea that the prairies of Posidonia oceanica
which were quite abundant in the past appeared like waving braiding aggregates.
The “tegnùe” consist of rocky materials which are often classified as beachrocks. Their
formation can be associated to zones of percolation of methane gas (CH4) that, producing
carbon dioxide (CO2) into the aquatic medium, and in the presence of calcium (Ca),
triggered the formation and concreting of carbonates (CaCO3).
The process took place in covered sediment layers and the rocks emerged form the sea
bottom later on due to erosion of the same sediment (Newton & Stefanon, 1978).
The “trezze” more often consist of organogenic materials, and they usually arise from
Posidonia meadows, which are mainly extinc nowadays. Over these meadows secondarily
developed the coralligenous (calcareous algae, briozoa, serpulids, mollusks, etc ...).
SAFEGUARD & VALORISATION
The “trezze” and “tegnùe” represent a sort of out-and-out local reefs. Several coastal
municipalities, research institutes, associations, divings, local authorities from Chioggia to
Venice, Caorle, Cavallino, Lignano Sabbiadoro, Grado and Trieste, have promoted during
recent years initiatives to deepen and diffuse the knowledge about these underwater
environments. These initiatives focused on the protection of the biological features of
these sites (for example their rich biodiversity, the role of nurseries, the ecological
worthiness, the importance for fishing), and on their valorisation along the lines carried out
for the promotion of surface land typical products or sites. The valorisation of this
underwater heritage can produce positive results in terms of scientific and educational
results coming from research, awareness, and dissemination activities. Furthermore, other
positive outcomes can directly derive from the importance of these sites to professional
fishing, their capacity to attract recreational fishermen and pleasure crafts, scuba divers,
and more generally the so-called eco-tourists. These sites make simbolically think to a
healthy and pulsating Adriatic Sea, and this in turns supports the winning idea of a tourism
strictly linked to territory and its peculiarities. Around
the “trezze” issue several interests and actors
(fishermen, citizens, school, associations, local
authorities, research) can collaborate to protect and
promote the Adriatic Sea, its bottoms and coasts. These
environments support common and shared traditions,
values, and the need for integrated policies for the
conservation and management of the environment.
Photographs by Luigi Paderni ©.
Reproduction forbidden.
All rights reserved ®.
THE NATURE OF SUBSTRATUM
The different origin and nature of the two kinds of substrata, as well as the most recent
evidences from the geomorphologic research in the Northern Adriatic Sea, make scientists
think that the overall distribution arrangement of these marine aggregates is not
overlapping the residuals of an ancient coast line which formed in the intertidal zone 3-4
thousand years ago during the alluvional period (Stefanon, 1969 & 1972), as it was
hypothesized in the past (A. Stefanon, personal communication). Some rocky aggregates
can be also found next to the trezze, and in some cases they could be associated to
percolation of freshwaters that emerging in the sea would produce carbonates and trigger
the concreting process (A. Stefanon, personal communication).
THE PICTURES BY LUIGI PADERNI
Within the above described context the images by Luigi Paderni (well-acquainted and
much-admired Friulian photographer), better known as “Gigi”, having as subjects the
phantasmagoric underwater life of the Lignano’s trezze, help the visitor know, appreciate,
and understand an hidden portion of the large environmental and cultural heritage of the
Region Friuli Venezia Giulia, a portion which is usually inaccessible to most of the public.
ACKNOWLEDGEMENTS & NOTES
The Ente Tutela Pesca of Friuli Venezia Giulia kindly thanks the Municipality of Lignano
Sabbiadoro and the FotoCineClub-Lignano for providing the photografic material.
Texts and graphics have been written and edited for ETP by Tiziano Scovacricchi (CNR
ISMAR, Venice, Italy).
CITED LITERATURE
1. Bellot, A., Gabriele, M. & Gallotti, D., 1998. Là, in mezzo al mar ... Sub, Anno XV, maggio, pp. 64-67.
2. Mizzan, L., 1995. Le Tegnùe. Substrati solidi naturali del litorale veneziano: potenzialità e prospettive. Azienda Sviluppo
Acquacoltura Pesca, Via Forte Marghera 151, 30173 Venezia-Mestre, 46 pp..
3. Newton, R. & Stefanon, A., 1978. Primi risultati dell'uso simultaneo in Alto Adriatico di side-scan sonar, sub-bottom profiler
ed ecografo. Memorie biogeogr. Adriat., Suppl. Vol. 9: 33-66.
4. Scovacricchi, T. & Burton, C.A., 1998. Lobster (Homarus gammarus L.) Research in the Northern Adriatic Sea. The Lobster
Newsletter, Vol. 11, July, N 1, p. 11.
5.Scovacricchi, T., 1998. Primi tentativi di rafforzamento degli stock di astice, Homarus gammarus (Linnaeus, 1758), in Alto
Adriatico. Biol. Mar. Medit., 5(3): 1455-1464.
6. Scovacricchi, T., 1999. Preliminary studies on stocking depleted populations of the European lobster, Homarus gammarus (L.)
(Decapoda, Nephropidae) onto the natural beachrock outcrops in the Northern Adriatic Sea. In: “Stock Enhancement and
Sea Ranching”, edited by B.H. Howell, E. Moksness & T. Svåsand, published by Blackwell Science Ltd., Fishing News Books,
Oxford, UK, Chapter 27: 393-400.
7. Stefanon, A., 1966. First notes on the discovery of outcrops of beachrocks in the Gulf of Venice. XX Congrès-Assemblée
Plenière C.I.E.S.M.M., Rapp. Comm. Int. Mer. Médit., 19(4), pp. 648-649.
8. Stefanon, A., 1969. The role of beachrock in the study of the evolution of the North Adriatic Sea. Memorie di Biogeografia
Adriatica, 8: 79-87.
9. Stefanon, A., 1972. Beachrock and paleogeography in the North Adriatic Sea. Rapports et procès-verbaux des réunions
C.I.E.S.M.M., 20: 605-608.