Life permeates every environment. In seas and lagoons, we meet it floating and swimming freely in the water – taking the name of nekton or plankton (respectively the organisms capable of contrasting the currents and those that let themselves be carried away by it) – as well as on and in the seabed and on any submerged structure – and it takes the name of benthos. The latter group is the protagonist of the present dialogue between art and nature investigated by the project ăquae naturografie leads by the contemporary artist Roberto Ghezzi and curated by START cultura and the Econtemporary gallery.

Benthic organisms inhabit firm or mobile substrates at all depths: from the uppermost stripe of the coast, submerged only temporarily according to the rhythm of the tide or the strength of the waves, to the deepest oceanic abysses. In the case of artificial substrates, such as hulls or port structures, where the presence of biological encrustations is undesirable, the term generally used is fouling, an English word which stands for “dirt”. Benthos biodiversity embraces a wide range of organisms, from bacteria to chordates (taxonomic group to which we also belong), encompassing algae, plants, sponges, corals, annelids, crustaceans, molluscs and numerous other groups. Many species, both vegetal and animal, are permanently “cemented” to the substrate, others are less firmly anchored to it, some others move freely, swimming or crawling. The life cycle of these organisms often includes planktonic larvae or other reproductive forms which have the role of propagating the species taking advantage from the currents. The larvae swarm innumerable: most will become food for other organisms, only few of them will reach adult size, settling even very far away from their parent’s home. A few square decimetres of surface could be populated by dozens of species, even considering only those that we can distinguish by the naked eye, the so-called “macro-benthos“, which is conventionally larger than one millimetre. Different species living together form composites communities characterised by complex dynamics, depending both on the reciprocal interactions, such as predation and competition, and on the interplay with the surrounding environment. The habitat they have chosen is in turn often substantially transformed.

We all know the incrustations that cover the hulls of boats and our “briccole” the three- piles dolphins marking the navigable canals, as well as those on the objects drifted ashore along the beaches, such as logs, plastic bottles or fishing floats. Some of them, look like real artworks crafted by the hand of Poseidon. Similarly, we can put a blank canvas into the water, in the lagoon and see what happens. Already in a very few days we could observe the appearance of thin coloured patinas, the first signs of life produced by invisible “pioneering” organisms: microbial biofilms and felts produced by microscopic algae. Days and months pass, and even macroscopic organisms take place, grow and succeed one another. Initially, these are a few opportunistic and tolerant species in large abundances, which are usually replaced by more balanced communities, characterised by greater biodiversity, complexity and stability. In certain habitats, however, this tendency can be contrasted by quick perturbations or prolonged stresses, such as changes in salinity, lack of oxygen, sedimentation, which favour the maintenance of immature stages: this is, in practice, a form of adaptation. The evolution of populations varies according to the characteristics of the substrate (composition, texture, three-dimensional structure and orientation in space) and the environment in which it is immersed and is modulated by seasonal cycles and inter-annual variability. In lagoons, the environmental factors are numerous and often characterised by intense and sudden changes in space and time. The most important are temperature, salinity, oxygenation, water exchange, light, nutrients, sediment composition, organic matter content and air exposure times. To these natural factors are added the different forms of pollution and the man-made modifications of the physical and biological environment, summarised in the term “human impact”. Finally, the fate of a community can also be determined by its initial state, in particular by the species that settles first, and which influences the settlement and development of the others.

Nevertheless, despite the numerous and intricate factors involved, it is possible to look backwards, in order to be able to recover information that cannot be obtained otherwise from observation of the living component of the ecosystem. They can give us information about the “environmental quality” that has a complex nature and is often difficult to define. This approach is called “bioindication”.

Whatever is the purpose of the investigation, the first step is to observe and describe carefully the organisms assigning them the correct names. To do this one must have the right tools and a good skill. Microscopes are essential to verify the morphological characteristics of each group of organisms and thus attribute a name to the species. Depending on the technology used, a different degree of detail can be achieved: if simple dissecting microscopes make possible to magnify every anatomical detail of organisms visible to the naked eye, other increasingly powerful tools, such as the scanning electron microscope, open up a new world, once hidden from human sight.

Let’s start now with an overall look at one of the canvases shown in the exhibition ăquae naturografie, just picked up from the waters of the Lagoon, where was immerse for a few months, so that nature, with its rhythms, would paint a story on it. It will be easy to observe a sequence of some horizontal bands, some of them narrow and others wide, each characterised by a pattern. It is thus possible to identify a vertical banding, a zoning, albeit restricted to a few decimetres of extension. At a closer look, the pattern of each band emerges as the product of a specific biological colonisation, added to eventual effects of chemical and physical agents. The settled species have extremely different sizes, shapes and functions. What can be observed are macroscopic vegetal and animal organisms, in particular the cover of sessile species, i.e., the ones anchored to the canvas, together with traces and vestiges of various types left by other macroscopic and microscopic organisms: biofilms and bioconstructions, erosive and degradative processes, exoskeletons. A terrestrial landscape is reproduced, we pass from conditions looking like an arid steppe to others of thick cover where we can see a miniature forest made up of both plants and animals, in which organisms capable of photosynthesis (primary producers) coexist with species that feed grazing on them. Other ones are detritivores, feeding on dead organisms, some others are filter feeders who sieve their food from the water and finally more or less ferocious predators appear.

The first story told here is the one of the incessant rhythm of the tides and the slapping of the waves on the coast. Thus, the zoning observed reflects the alternating conditions of emersion and immersion, their duration and frequency. Exposure to the air with consequent dehydration, is a highly stressful condition and determines a selective pressure on the organisms, favouring very stringent morphological and physiological adaptations and a vertical sequence of different biological communities in the span of a few feets. At the upper limit, marking the average level of high tides, there is only a dark belt made up of a film of blue algae (cyanobacteria), called by the Venetians “comun marin” and once used in Venice as a reference line for building the city. Below this line, a green band of algal mat follows. In these first two bands there are generally few herbivores or filter-feeders, with little or no ability to move, capable of sealing themselves inside a shell or other protective structures during the frequent periods of emersion. Descending towards lower levels of the intertidal zone, below than the middle sea level, the emergence becomes increasingly short, more time is spent underwater, other types of organisms appear and the biodiversity increases. Among the vegetal seaweeds (macroalgae) prevail on microalgae. The animals are sessile filter feeders: bivalves such as oysters and mussels, serpulid polychaete worms, sponges, bryozoans, solitary and colonial sea squirts. Other macro-invertebrates, herbivores, detritivores and predators are freely moving in this space: sea snails (gastropods), small amphipod crustaceans (sea fleas) and isopods (looking like sowbugs and water slaters), decapods such as shrimps and crabs. In the northern Adriatic, the tide is a key factor in governing the landforms of the lagoon and structuring biological communities. Naturally, the described banding effect of the tides occurs when the substrate is bound to an absolute height, whereas when it is suspended from a floating structure the effects of the waves prevail, resulting in a compacted zoning.

The list of benthic species found, particularly in the lower zone, which is more frequently submerged and therefore more stable, varies in terms of species richness and composition depending on the site of installation. A second theme therefore emerges, concerning the differences between the internal lagoon close to the mainland and the river outlets, and the areas in the vicinity of the sea inlets and more generally to the variety of the lagoon environments. What might at first appear to be a homogeneous environment is crossed by strong spatial variations in the natural chemical and physical conditions, largely along the same prevailing land-sea (or freshwater-marine water) direction. This “composite” pattern is made up by three key variables, the water exchange and salinity, which increase approaching the sea, and the concentration of nutrients in the water column, which instead decreases near the sea. This land-sea gradient has strong effects on the structure of the benthic populations: aquatic life in the internal areas of the lagoon is stressed by the harsh environmental conditions and fewer species can cope. Consequently, biodiversity decreases and the relationship between species sensitive and tolerant to environmental pressure changes, as well as among the different roles in the food web. The community highlights conditions of natural stress that become stronger as the distance from the sea increases. This fact has a very important secondary effect on bioindication since it is very difficult to distinguish the negative effects produced by human action, such as for example pollution from organic loads, from the effects of stress naturally present in lagoons, with consequent difficulty in assessing environmental quality.

Another story that can be told about the changes caused by humans in the global distribution of biodiversity. Among the organisms found on our canvases we found some alien species, more correctly called “allochthonous” that means they come or came from other seas even very far. Among these, some are present with high abundance or biomass, sometimes placed in key roles in the food web, determining potential effects on biological communities and sometimes profoundly transforming the habitat, as real “ecosystem engineers”. There are numerous non-native species found in our canvases. Two of the most evident are Amathia verticillata and Tricellaria inopinata, both belonging to the phylum of bryozoans, a group of filter-feeding colonial organisms that develop important filamentous and branched clusters. These two species well represent the great changes occurring in biodiversity at a global scale: the first is native to the western Atlantic, the second to the Pacific. Both are now stabilised in the Lagoon of Venice and are listed among the most abundant bryozoan species. The introduction of non-native species can follow different modality and paths: sometimes it occurs intentionally, as in the case of the Manila clam (Ruditapes philippinarum, Caparozzolo), more often it is accidental, for example in the ballast waters or together with the fouling growing on the hulls of ships, or as a consequence of commercial trade linked to aquaculture. The Suez Canal (currently undergoing further expansion) is another important route for the diffusion of species from the Indo-Pacific region. The climate changes underway, in particular the increase in sea temperature, also to favour the processes of diffusion of sub-tropical or tropical non-native species towards our latitudes. Lagoon environments are recognized as relevant “hot spots” for the introduction of alien species, and this is particularly true for the Lagoon of Venice, where there is an international port and a relevant aquaculture.

For the last story we are going to tell, we will use one of the most advanced microscopy technologies, which is the Scanning Electron Microscope, (SEM), which can give us a 3D image. Observing the microscopic world that has colonised the new habitat provided by the artist, among the various forms some vegetal organisms formed by a single cell stand out for their beauty and composition, capable of building soft carpets on any surface immersed in water. These are organisms belonging to the microphytoplankton widespread in all aquatic environments: in coastal areas where light penetrates to the bottom, in lagoons, marshes, rivers and lakes and in any environment where fresh or salt water is present, including puddles and canals. In shallow environments characterised by moving waters such as lagoons, the microphytobenthos can be lifted by the water movement from the substrate and conversely the microphytoplankton floating in the water can settle down on the bottom when the turbulence stops. Like terrestrial plants, they are photosynthetic organisms. The taxonomic group most represented in the canvases is represented mostly by Diatoms: individual plant cells of dimensions up to 10 times smaller than the diameter of a hair, characterised by a vitreous (siliceous) external coating called frustule, decorated with characteristic sculptures which, due to their attractiveness and elegance, do not they have nothing to envy to the best human abstract art. These forms have a precise functional meaning, allowing the exchange of ions or light necessary for photosynthesis and allowing the movement of the individual. Microalgae correspond to about 95% of all marine biomass and up to tens of millions of them can live in one litre of water in our seas, lagoons, rivers and lakes. They constitute what is defined as “the first ring in the trophic chain”. These tiny organisms compose a real global invisible forest that produces about half of the oxygen we breathe and at the same time removes about half of the carbon dioxide we produce from the environment, thus helping to keep the greenhouse effect and the temperature of the planet under control. Briefly, this invisible submerged forest protects us from ourselves.

Let us therefore be seized by the charm of these canvases that whisper to us barely hinted stories of places and times, let ourselves be enveloped by their intriguing beauty to go further and read other stories wrapped up in other canvases of time and space.