Benthic foraminifera as environmental indicators in extreme environments. The marine cave of Bue Marino (Sardinia, Italy)

The coast of the Gulf of Orosei (Sardinia, Italy) consists of impressive cliffs set up on dolostones and limestones characterized by wide karst systems connected to the sea. Marine caves, which are part of these system flooded by seawater through marine entrances, may be considered as extreme environments because of wide spatial and temporal environmental variability due to changing marine and terrestrial contributions. This study presents the results of the third survey carried out in summer 2016 in the Bue Marino cave, as part of a research project started in 2014 aimed at the application of Benthic Foraminifera (BF) as ecological indicators in Mediterranean marine caves for the identification of different habitats and their environmental interpretation. Sediment and water samples were collected from a total of 25 stations from two distinct sectors of the cave (North Branch and Middle Branch); sediments were analysed for living and dead BF and grain size, while Temperature, Salinity, pH and Dissolved Oxygen were measured in water samples collected close to sediment water interface. Two main foraminiferal assemblages, with distinct characteristics with respect to the typical Mediterranean shallow-water ones, were recognized by means of Hierarchical Cluster Analysis and Non-metric Multidimensional Scaling, and a Canonical Correspondence Analysis deduced their environmental significance. A well oxygenated, less saline environment with coarse bottom sediment, correlated with a mixed calcareous-agglutinated assemblage (Gavelinopsis praegeri, Rosalina spp., Eggerelloides advenus and Reophax dentaliniformis) with high species diversity (H-index 2.32–3.57) and low foraminiferal density, was exclusive of the North Branch. A scarcely oxygenated, more saline environment with fine bottom sediment enriched in vegetal debris was related to a prevalently agglutinated assemblage characterized by low species diversity (H-index 1.60–2.68), with high dominance of E. advenus (up to 83.6%) associated to Ammonia tepida, and high foraminiferal density, recognized in the Middle Branch. These different environments were interpreted considering the different modes of feeding the karst systems of the two branches. They also corresponded to two distinct ecozones, Entrance and Confluence, already recognized in earlier studies. The environmental significance of the foraminiferal ecozones recognized in this study and their comparison with the ones identified in the previous years, helped to consider the ecological zonation as a tool for detecting seasonal and, possibly, long term annual environmental variability in the marine system

Morphology and hydrogeology of a complex sinkhole system in a remarkable archaeological site along the Adriatic coastline (Apulia, S Italy)

The Grotte della Poesia karst system is a complex of caves, sinkholes and submerged galleries, located along the Adriatic side of southern Apulia (Italy). In detail, the system consists of two main collapse sinkholes (Grotta della Poesia Grande and Piccola), connected through sumps with an intervening cave, and linked to the sea on two sides. Sinkhole development was strongly favoured by hyperkarst processes due to intermixing between fresh and salt water, and by the resulting increased aggressivity on carbonate rocks. The overall system is within the remarkable archaeological site of Roca, which incorporates remains from late Bronze to Medieval age (Scarano 2010). In particular, Grotta della Poesia Piccola hosts along its walls thousands of Messapian inscriptions dating back to IV-II centuries B.C., which are still the object of study by archaeologists. Local stratigraphy in the area consists of weak, laminated calcilutites and fine calcarenites alternated to coarser macro-fossiliferous and bioturbated calcarenites (Middle-Upp. Pliocene). Differences in permeability among the layers originate a multi-layered water table. To this, name of the caves has probably to be related, since the word poesiacomes from the local dialect (in turn, from ancient Greek), to indicate a spring or water emergence (Parise et al. 2003). A spring would therefore have been present within Grotta della Poesia Piccola, but at present is not visible anymore, probably due to lowering of the water table. Tectonically, wide folds with N 150 E axes (about parallel to the coast) characterize the area. They determine the presence inland of a wide marshland (Tamari), that has been interpreted as the inner and protected harbour for the ancient town of Roca. The Adriatic coastal landscape is characterized by a number of marine terraces resulting from the combined action of regional uplift and glacio-eustatic sea level changes. The coastline is very articulated, with 10-15m high cliffs, intensely affected by slope instabilities (Delle Rose and Parise 2004; Lollino et al. 2021). Within this geological setting, we are carrying out detailed speleological and diving explorations aimed at fully surveying the intricate system of caves (in both aerated and flooded conditions), as a mandatory step in order to identify the sites most susceptible to rock instabilities. Since the site is highly touristic, it is crucial to recognize the likely hazards, and to properly delimit the most dangerous areas. The surveys are also going to be used to better understand the hydrogeological situation, and to verify the possibility of presence of submarine springs in the coastal area and its surroundings

Submarine springs in the Gulf of Taranto (Italy): geology, hydrogeology and cave diving explorations

In coastal karst lands, due to difference in permeability among contiguous strata, emergence of springs may occur inland or as submarine springs, as in the Gulf of Taranto (Italy), marking the S limit of Murge, the largest karst sub-region in Apulia. Groundwater from N-NW feed some inland springs, sometimes originating small rivers, with Tara as the main significant. In addition to surface waters, submarine springs are present within the gulf, namely in Mar Piccolo of Taranto, an over 20 km2 wide basin (10-14m depth) consisting of two bays with elliptical shape, connected through a channel. In the N sectors of the bays 34 submarine springs have been identified. Locally called citri, a word of Greek origin, deriving from history of Taranto (founded as a Greek colony), they work as thermal regulators for the water temperature, allowing extensive development of mussel farming. The groundwater emission sites are characterized by funnel-shaped morphology with a circular profile at the sea surface. In the past, attempts were done to tap these waters (Cotecchia et al., 1990), but technical and engineering problems, brought to abandon such activities. In the Murge district the Cretaceous limestone aquifer is covered by Plio-Pleistocene calcarenites, clays and terraced marine deposits, with secondary porous aquifers flowing within these latter. Origin of the citri is related to surface dismantling and erosion of the cover, and to emergence of the confined water hosted in the limestones. In most of the cases, it comes out in wide areas, without a clear karst conduit. Among the few caves explorable by man, there is Citro Galeso, at the W bay: with a diameter of 20 m, and 18m depth, it has discharge of 0,750 m3/s. Inventoried since the first half of the XX century (Cerruti, 1938), only recently the distribution of citri was studied in detail (Valenzano et al., 2018). The largest spring (Saint Cataldo’s eyes) is located just outside the two bays, in Mar Grande: 200x300 m-wide, it consists of two cavities, reaching depth of 48 and 52 m, respectively, below sea level, and deepening for 20 additional meters. To improve the hydrogeological knowledge of the area, we are carrying out a variety of scientific activities, starting from exploration and surveying of accessible springs. A significant role is being attributed to the study of the cave systems, as regard their distribution and pattern network. As outflow yield and flow velocity data are not yet available for all citri, some measurements will be done at this aim. In addition, water samplings will be taken for characterizing the chemical constituents, and for assessing the presence and nature of pollutant

Mitigazione del rischio da dissesti in un’area a forte valenza turistica ed archeologica: Roca Vecchia e Grotte della Poesia (Melendugno, Puglia)

Il litorale adriatico pugliese offre numerosi tratti caratterizzati da notevole attrazione turistica data la bellezza paesaggistica dei luoghi, a cui si combinano di frequente siti di grande importanza archeologica. Il territorio di Melendugno, con il promontorio su cui insiste il centro fortificato di Roca Vecchia (De Giorgi, 1922; Pagliara, 1987, 2001; Scarano, 2010) è certamente tra quelli di maggiore interesse. La presenza di depositi carbonatici fortemente affetti da fenomeni carsici, e interessati da erosione e crolli, rende problematica la gestione di questi luoghi a forte attrazione turistica, specie nel corso della stagione estiva

Benthic foraminifera as proxies of marine influence in the Orosei marine caves, Sardinia, Italy

As a result of their location at the boundary between marine and continental domains, marine caves are affected by wide spatial and seasonal environmental changes. Only recently have benthic foraminifera been recognized as reliable indicators for the ecological zonation of these environments. The present study is focused on two marine caves of the Orosei Gulf, Sardinia, Italy: Bue Marino and Bel Torrente. It investigates the spatial and seasonal variability of benthic foraminiferal assemblages relative to sediment grain size and water parameters (temperature, salinity, pH, and dissolved oxygen) collected during two campaigns in August 2014 and April 2015. The results from 2014 have been partially published. Based on a comparison of the results of the two campaigns, the considerable reduction of foraminiferal abundance in Bel Torrente was deduced to occur because of the strong freshwater flows occurring during the rainy season; in Bue Marino, the less severe water flow allowed the identification of both living and dead foraminifera, although strongly reduced in number. These identifications allowed benthic foraminifera to be used to define the ecological zonation. Entrance, confluence, and transitional ecozones were identified in Bue Marino cave on the basis of species abundance. The second ecozone, not recognized in 2014, was correlated with plant debris at the confluence of the two cave branches. The other two ecozones, which are characterized by the faunal shift from hyaline- to agglutinated-prevalent assemblages, were attributed to the gradient of abiotic parameters detected from the outer to the inner portions of the cave. In both campaigns the same ecozones were recognized in terms of species composition, with exceptions being found to different extents as a result of seasonal variability. As the distribution of foraminiferal ecozones is conditioned by a decreasing gradient of marine influence, long-term monitoring may be regarded as a promising tool for future studies on sea-level change