Scientists reveal the origin of one emblematic Italian marine reserve

At about 24 meters deep, at the bottom of the Gulf of Venice, and opposite the Italian coasts, a dazzling natural submerged reserve: the Tegnùe di Chioggia. It is a corallingenous formation –made up of embedded calcareous algae that develop in low temperature seas- which extend to four meters above and ten kilometers along the seabed. This place has been studied since the end of the eighteenth century. The origin of this structure could be recently revealed thanks to an interdisciplinary study performed by Argentine and Italian experts in which one CONICET scientist at La Plata. The research has been published in Scientific Reports, a journal of the Nature group.

Eleonora Carol is a CONICET associate researcher at the Centro de Investigaciones Geológicas (CIG, CONICET–UNLP) and is the only Argentine author of the study allowed scientists to understand how that area made up of the embedded algae, corals, sponges and biozoos. “It’s an emblematic place in the north of the Adriatic Sea that has always called our attention for those coralligenous formations. In general, this area used to be studied due to its biological interest, but people did not know why it had that morphology and why those formations were present there and not somewhere else”, the scientist comments.

For more than five years, the experts –geologists, oceanographers, geophysicists and biologists –of the Istituto di scienze marine (ISMAR) under the scope of the Consiglio Nazionale delle Ricerche (CNR); the Università di Padova, Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), the Istituto superiore per la protezione e la ricerca ambiental (ISPRA) carried out around 200 dives in the depths of the gulf to collect samples of rocks, sediments and water to study the geology, geomorphology and hydrology of the area.

“For their development, this type of formations needs the bed to be cemented, that is to say, to be solid. This is the strong surface on which these organisms grow”, she explains and describes: “In the dives, we obtained control samples of that substrate -which was called Piedra Rosetta by my Italian colleagues- due to the key rol that rock played to understand the origin of the coralligenous formations of the Gulf of Venice. Through the Carbon-14 dating method, it was possible to know the estimated date in which the cementation process began, and how the environment was at that time.”

One of the samples of cemented sand obtained from the base of the coralligenous rocks allowed scientists to date at around 9 thousand years BP the entrance of the sea in the area, and around 7 thousand years BP the cementation of the layer that led to the inlay of the bioconstructor organisms. “At that time, there was a shallow marine environment with paleochannels filled with sand that worked as aquifers that discharged into the sea”, the expert explains.

Luigi Tosi, ISMAR researcher, comments that “it was demonstrated that the coralligenous formations have been developed along the old sinuous waterways present 20 thousand years BP, when the sea level was 120 meters lower than the current one and Venice was still a plateau. Later on, when it rose and the Venetian plain flooded, those old channels filled with sand turned cemented. The sand became a rock because there was a very particular mixture of fresh groundwater at the paleochannel and salty water from the sea. This, together with other biological factors favored the cementation.  The presence of coralligenous structures built on the remains of the old cemented fluvial channels had not been recorded at the Mediterranean Sea.”

Her colleague at the ISMAR, Sandra Donnici, adds: “It is important to understand the origin of this formation but not only form the biodiversity and geodiversity point of view, but also from the hydrogeological aspects, such as to know what happens in the relationship between the fresh groundwater and the marine one, what could lead to great contributions for studies on geology, oceanography and biology.”