Urban Environment

The city fauna

A lot of animals have found in the city of Venice a hospitable place where to live, and the reasons that have led them to this choice can be listed in the following way:

The city flora

When you think about the city flora, most of all in a city such as Venice is, the public gardens or the private ones, beautiful green corners hidden within the courtyards come to mind.
But there is a smaller and less hidden world that discloses to the eyes of the most careful observers and that populates the banks, the fondamenta and the city walls.
On the bank walls, in the strip of the water sprinklings still influenced by the presence of the brackish water of the canal, species accustomed to the salt environments as the sea fennel (Crithmum maritimum), the sea lavender (Limonium vulgaris) the hastate orache (Atriplex hastata) can be found. Finocchio di mare (Crithmum maritimum)
Swimming up to the bank you reach the border of the fondamenta: there, as they are so near to the canal, the treading down causes less trouble and the plants can reach bigger dimensions. Moreover, the influence of the salt water of the canal decreases, while the level of organic matter, hoarded up in the cracks among the stones increases. In this area the amaranth (Amaranthus retroflexus), the lamb’s quarters (Chenopodium album), the Bermuda grass (Cynodon dactylon), the dandelion (Taraxacum officinale) can be found.
Moving to the inside of the fondamenta, the trouble caused by treading down increases and therefore both the species and the growth of the plants change. There, smaller plants usually flattened down to the ground, with small flowers and leaves that can survive to the treading down taking shelter into the cracks among the stones, can be found.
The Greater plantain (Plantago maior), the Birdseye pearlwort (Sagina procumbens) and the Knotgrass (Poligonum aviculare) belong to this community.
Along the walls or on the sides of the bridge steps, where the trouble caused by treading down is the lowest and some mould is hoarded up, another kind of vegetation develops. The horseweed (Conyza canadensis), the shepherd’s purse (Capsella bursa – pastoris), the bittercress (Cardamine hirsuta), the squirrel-tail grass (Hordeum murinum), the annual blue grass (Poa annua), the common groundsel (Senecio vulgaris), the kitchen-garden purslane (Portulaca oleracea), the vervain (Verbena officinalis) can be found there.
Other plants do not have to face the problem of treading down, as they grow up on the walls of the houses and on the arches of the bridges. The most common of these is the Pellitory of the wall (Parietaria officinalis), ollowed by the Kenilworth ivy (Cymbalaria muralis). The first organisms to colonize the walls of the building and of the bridges are the lichens, that are able to crumble the rock and to prepare the ground for other more demanding plants. Parietaria (Parietaria officinalis)
LThe plants that can be found in the city have several methods to be able to survive to the winter: in some of them (Emicryptophyte) the leaves keep on growing as a basal rosette, that, being flattened down, exploits the heat coming from it and is protected by the dead leaves of the plant itself. Some others (Terophyte) spend the winter as seeds that germinate only when conditions become favourable.
The seed dispersal is made efficient by both the elevated quantity of seeds, that ensures more chances of success and by the typology of the seeds, that are often provided with a pappus or are very light anyway. These strategies let the seeds reach favourable environments, even if they are very far from the mother plant.

Venice canals

In order to discover a particular typology of flora and fauna in the Venice lagoon, it isn’t always necessary to look for special environments, but it is enough to look at the banks of the canals that run through the city more carefully.
A big variety of both animal and vegetable organisms populate the banks, both above and below the water level.
The best period for observation is springtime, when the biological activity of the organisms reaches the highest levels, and especially during the phases of low tide, when the visible strip is the largest.
The bank environment of the Venice canals can be divided into three easily distinguishable strips:

The strip of the water sparkling

This strip is reached by the sprinklings of the water, and only occasionally is affected by exceptional tides.
Its width varies, according to the intensity of the wave motion , from 50 to 100 centimetres.
It is populated by highly specialized organisms: the ground organisms must be able to bear the salinity and the periodical floods, while, on the contrary, the sea ones must be able to resist during the long periods of emersion.
On the upper part of the walls along the canals, but also on the steps of the watergates of the palaces, you can see a green patina, made up of the green microscopic algae that indicate the maximum height the sprinklings can reach.
The first animal organisms that can be found in this strip are the air-breathing isopod crustaceans: the Italian sea roach (Ligia italica) and the Sea slater. Both are very similar to the woodlice, but the sea roach is distinguishable for the speed with which it goes back when the wave comes.
In the area Littorina (Littorina littorea)

of transition between the strip of the water sprinklings and the one below the common periwinkles that are gastropods molluscs (Littorina littorea) live. These snails live on more stable substrata than the bricks, that are easily friable, and therefore most of all on the stones that offer a good and constant presence of the seaweeds, that represents their food.
They live in small groups in the area that is regularly under water during the high tide, and so they are observable both with medium and low tide. During wintertime they take shelter in the narrow cracks that are not reached by the water, and even if they are a sea species they can resist to relatively long periods of emersion.
In this area the Enteromorpha (Enteromorpha intestinalis), can be found, that here gets accustomed to the difficult conditions due to the periodical emersions reducing its development to a minimum.

The strip of tidal excursion

This strip, often called intertidal area, in Venice is about 1 metre thick.
One can find Crustaceans that stick directly to the substratum and that can even be found hoarded up one against the other on the stakes embedded in the caranto (a hard layer of clay).
The Acorn shells are cirriped crustaceans. That means that they are provided with limbs that are employed to create small whirlpools in order to convey the food towards their mouth. They don’t look like other cirripeds, as the adaptation to a sedentary life has determined several changes and only during their youth stage these organisms can be seen swimming freely.
The more abundant and characteristic species that can be found along Venice canals are the Striped barnacles (Balanus amphitrite) and the Poli's stellate barnacles (Chthamalus stellatus).
Mussels can often be seen being attached to the valves .
They can bear periodical emersions thanks to two small mobile plates situated on the top of their body, that allow on one hand the contact with the outside when they are submerged and on the other to isolate, keeping in the inside the surrounding water environmental conditions during the emersions.

Besides the acorn shells, the Limpets (Patella coerulea), gastropods molluscs, can be found. Their shell perfectly fits to the substratum on which it is situated thanks to its muscular foot, that perfectly sticks at it, and this strategy has a double aim: to defend from possible aggressions and to keep a sea water supply inside the shell in the periods of emersion.
In this environment the seaweeds find the most suitable situations to their development, and the number of different species increases.
The Enteromorpha reaches its maximum vegetation development, and the red alga (Porphyra leucosticta), banded weeds (Ceramium rubrum), and the green laver sea lettuce (Ulva lactuca) make their appearance too..
The Enteromorpha and the green laver sea lettuce are green alga, while the Porphyra and the Ceramium are red alga, whose presence is justified by the fact that the water in the Venice canals is very muddy and doesn’t allow the wavelenght of the green band to penetrate, while the green band can cross the column of water without suffering great absorptions.
Among these seaweeds the Crustaceans as the Green Crab, whose females are called masanete, can be found. These decapods can be found in the canals especially in spring, when they move from the sea to the lagoon, and in autumn, when they go back.
During its growth the crab, once this has become too small, leaves its carapace , and during the moult its body is soft and has no defences: this phase lasts a few hours during which the crab becomes the so-called moeca.

The strip of low tide

Besides the seaweed, the Molluscs and the Crustaceans, the peoci, the Mussels (Mytilus galloprovincialis) make their appearance. They stick to the substratum on which they live with the byssus, which is made of filaments produced by a gland (the byssus gland) and that solidify when in contact with the water.
n the areas in which the emersion is the most frequent the dimensions of the mussels are smaller because the periods during which the mytilus can feed on small seaweeds and particles of organic material present in the water are shorter.
The mussel is a sessile organism, co the main surviving strategy consists in forming very thick shoals, in which their sharp borders, all turned towards the outside, represent a solid and with difficulty penetrable carpet (from Bonometto L., Mizzan L., “Forme e significati – Osservazioni e riflessioni sugli animali del nostro mare”, Quaderni del Museo Civico di Storia Naturale di Venezia, Suppl. to Vol. XXXVIII (1987) of the Bollettino del Museo Civico di Storia Naturale di Venezia).
During the low tide it is possible to see Star ascidians, Sea squirts, Sponges, Sea anemones.
AOther species typical of this environment aren’t sessile and have the chance to move to look for more favourable conditions (from Pellizzato M., Carlotti G., “L’ambiente di riva dei canali di Venezia”, in “Lavori” della Soc. Ven. Sc. Nat., vol. 5, supplemento ad uso didattico, pp.50-64, 1981).
Venice canals offer an ideal environment in which to study the so-called fouling, phenomenon, that interests the submerged objects and it is performed by sea organisms. Observing a stake or some other artificial structures stuck into the canal, it is interesting to notice how the colonization of this new environment follows a precise succession which is also easily observable in any other substrata stuck with the same methods.
The first organisms are the seaweeds, that do not need a special substratum on which to settle, as they, having no roots, take their nourishment directly form their thallous surface. The seaweeds represent the primary fouling. Afterwards the mussels settle on them (the so-called secondary fouling) while acorn shells are indifferent to the colonization degree of the substratum and they can belong to both the primary and to the secondary fouling ( from Cornello M., “Contributo allo studio ecologico delle comunità bentoniche sessili nella Laguna di Venezia: struttura e dinamica in relazione ai periodi d'insediamento" – Degree Thesis, A.A. 1994-95, University of Padua).
The outlined situation is typical of the canal environment, but it is strongly influenced by pollution, that, most of all in the canals with the least water change, causes a drastic reduction in the species, leaving free range to the most resistant ones.

	DISSEMINATION

Urban environment