Why a visit to the Natural Science Museum in Venice ?
On November 29th 2010, our class went to Venice to visit the Natural Science Museum. We went there to attend a laboratory on “The Atlas of the lagoon of Venice”. This activity is one of the many we are carrying out on the environment for the Comenius Project “Immediate Surroundings”.
We decided to study the Venetian lagoon because it is not only near us in distance, but also for sentimental and health reasons. In fact, we think that if we do not know the environment we live in and its rules, we cannot love it and take care of it properly.
The laboratory was organized and financed by the Venice City Council in the field of its educational activities. Its aims are to know the Atlas and to analyse biodiversity in our lagoon.
What is the Atlas of the lagoon ?
The Venetian lagoon is one of the most interesting environments in the world and its existence itself is threatened. This is the reason why a lot of research institutes study it systematically. The Atlas has been created in order to bring together all the studies in a single book. Quite a difficult job ! The problem was solved using a visual approach. Graphic representations have a huge capacity to summarise data and facilitate their comprehension.
The creation of the Atlas was a project supported by the Venice City Council. The work began in 2002 and, after four years, a wonderful volume was published and now you can consult it surfing the net at http://atlante.silvenezia.it
And what about biodiversity ?
As you surely know 2010 was dedicated to the International Year of Biodiversity. The biologist who conduct the laboratory explained to us that because of habitat transformation a lot of species are being threatened and that the human impact all over the world is reducing significantly the number of species. Specialists call this phenomena “Holocene extinction”.
Biodiversity is the existence of a large number of different kinds of animals and plants which make a balanced ecosystem. It is the result of evolution, a slow process of adaptation to the environment. A lot of species of animals and plants have evolved and adapted themselves to the environment in the Venetian lagoon. Scientists call them native species, but in other part of the world other similar species live. Man is moving species from one part of the globe to another at an unprecedented rate. In the last thirty years other species were introduced in the lagoon and a slow silent competition began. This new non-native species arrived in very different and even strange ways, both directly by means of man for economic reasons and accidentally such as the crab Dyspanopeus sayi which was introduced by means of the water put into ship coming from Japan as ballast. Yes, like a clandestine!
We were taught to distinguish Venetian native species from the other ones by means of a microscope and we have to separate one from the others. This activity was very interesting. But it was more interesting to learn how these species arrived in the Venetian lagoon and the state of the competition. We have analysed four examples of native species versus non-native. Following you’ll find further information.
Origin of Cassostrea gigas: Japan
Introduction way: In 1966 this species was introduced into the Venetian lagoon for commercial purposes. In fact, it is edible and its introduction allowed the survival of oyster breedings, in particular after the reduction of native Ostrea edulis.
Result of competition: extinction of the native species
Cassostrea gigas has probably caused the extinction of Ostrea edulis in the Venetian lagoon.
Origin of Dyspanopeus sayi: the North American Atlantic coasts
Biology: A species which is tolerant both to temperature and salinity variations and is able to invade ports and estuaries. It demonstrates a good capacity to tolerate water pollution.
Introduction way: The first reports of its presence in the Venetian lagoon were in 1992 when it was already widespread in the lagoon and even in the urban canals. Probably its presence in the lagoon goes back to 1978/79. It is thought that this species was introduced by mistake by means of the water contained in the ships that arrived in the ports or through the imported shellfish.
Result of competition: coexistence of the two species
This species has successfully colonized all the lagoon habitat. After a period of great expansion, now Dyspanopeus sayi is less frequent than in the past. The non-native crabs live in microhabitat such as thick mussel or oyster reefs.
Origin of Ruditapes philippinarum: widely spread in the Pacific Ocean
Biology: It is a bivalve shellfish that filters water through its two siphons (one in and the other out) catching organic matter and phytoplankton as food. It lives in eutrophic habitat and demonstrates a more rapid growth than native species. it is even more tolerant to chemical pollution in the water and so it is more competitive.
Introduction way: It was introduced into the Mediterranean sea along the French coasts in 1980 for commercial reasons. Later, in 1983, it was introduced into the Southern part of the Venetian lagoon. From 1986-1987 this species had adapted itself to its new habitat.
Result of competition: coexistence of the two species
This species is to be found in highly polluted urban and industrial zone and for this reason it presents serious problems both for sanity and environment. Because of its great productivity and high commercial value it is collected in large quantities with extensive damage to the environment. In the Venetian lagoon high powered fishing boats are used and cause severe damage to the seabed and to organisms which live in the benthic zone. In fact, many species do not show the ability to reform and recolonize like Ruditapes philippinarum so the whole ecosystem is threatened.
Origin of Sargassum muticum: Japan
Biology: An alga of large dimension of over one metre in length.
It is like Cystoseira barbata but has numerous round cysts inserted in short peduncles which permit the species to float.
Introduction way: It was first introduced along the European Atlantic coasts and later into the Mediterranean Sea. It arrived in the lagoon in 1992. Its introduction was by chance probably through the importation of fish.
Result of competition: coexistence of the two species
Characterized by rapid growth and high density of installation Sargassum muticum forms dense stretches on the seabed. Extremely competitive with other species, in the Lagoon it is particularly widespread. Extremely competitive with other species, in the Lagoon it is particularly widespread during the winter and spring period then it retreats to leave space to Cystoseira.
If you are interested in this topic, visit the website of the Natural Science Museum of Venice http://www.msn.ve.it/index.php?pagina=inambiente_view&id=4
