Search

International audience; Deep-sea environments in the Mediterranean Sea have been widely degraded over the past decades and thus there is an urgent need to implement protection measures. Within European Union's Mediterranean waters vast extensions of the deep-sea ecologically relevant ecosystems have been protected by integrating them to the Natura 2000 network. Inside the French Exclusive Economic Zone, this network is currently expanding to off-shore areas, beyond 12 nautical miles. In this study, we characterized megabenthic biodiversity on target features located inside a designed site of the south west Corsican margin, particularly on a volcanic promontory on the south flank of the Ajaccio submarine canyon and a wall of the Valinco Canyon, between 1690 and 2250 m depth. By means of a fine scale three-dimensional photogrammetric analysis, four megabenthic assemblages segregated by substrate were identified. Hard substrate assemblages were characterized by the presence of sponges, polychaetes, gastropods and the squat lobster Munida tenuimana while soft sediment assemblages were characterized by the elpidiid holothurian Penilpidia ludwigi and an unidentified sabellid. Highest densities were registered on serpulid thanatocoenoses, which hosted widespread patches of an unidentified encrusting sponge. Lebensspuren had a diverse origin likely deriving from the activity of epibenthic, infaunal and bathypelagic organisms. In general, litter was not abundant at these offshore sites: in the Valinco site, it had both a marine and land-based origin while at the even more offshore Ajaccio site, it was mainly marine based. More extensive surveys would be advisable to confirm this trend. This study provides new insight on the ecology and diversity of Mediterranean deep-sea environments in the 2000 m bathymetric zone, highlighting the enduring knowledge gap surrounding orographically complex deep-sea escarpments in the basin.

Seamounts represent ecologically important marine environments and undeniably play a crucial role in the functioning of the deep-sea ecosystems, thanks primarily to their contribution in supporting offshore benthic and pelagic biodiversity. In the last decades, these features have received attention in all oceans of the world, but they were relatively overlooked in the Mediterranean Sea. In particular, the Ligurian Sea hosts six major structures, whose summits, ranging from 150 to nearly 2000 m depth, are virtually unknown from the biological point of view. The summit region of the Janua Seamount, located approximately at 40 nautical miles off the harbour of Genoa at 810 m depth, was explored for the first time using Remotely Operated Vehicles. The sea bed topography is characterized by a heterogeneous hard bottom, dominated by sub-fossil thanatocoenoses of Lophelia pertusa (Linnaeus, 1758) covered in a thick Ferrous-Manganese crust, and colonized by a scattered bathyal assemblage dominated by hexactinellids and benthic cnidarians showing a distinct regionalization around the summit. Cnidarians observed in this site include a rare Atlantic bamboo coral (Isididae, Chelidonisis aurantiaca Studer, 1890), described herein for the first time for the Mediterranean Basin. These findings provide new information on the biogeographic patterns of colonization of the bathyal Mediterranean fauna but also highlight the large knowledge gap that still exists for deep-sea biodiversity of this basin.

The Norther Adriatic circalittoral is mostly characterized by monotonous seabeds, whose dominant biocoenosis ia the muddy detritic. They are interrupted by precoralligenous detritic bottoms and biogenic formations, such as the rocky outcrops called Tegnue and the reefs of Cladocora caespitosa. These habitats are severely endangered, due to intensive fishery and other environmental disturbances. To manage their protection, the knowledge of their extent and the classification of the habitat type, in agreement with the most recent Directives and International Protocols, is essential. No general consensus exsists on the criteria to categorize the coralligenous and a number of definitions is proposed based on noth-western Mediterranean evidences. The available list of species, as well as the main engineering species, are known from these areas, while they cannot be considered to be constant in the rest of the Mediterranean. This paper represents an up-to-date contribution to the knowledge of compoosition and distribution of circallitoral biocoenoses and to the understanding of coralligenous formations in the Northern Adriatic. The study is based on literature data and on most recent researches carried out on rocky outcrops off the Gulf of Venice and Trieste, and on the circallitoral detritic bottom off the Slovenian coast. Rocky outcrops display a wide range of morphologies that, together with environmental factors and human pressures, influence the habitat complexity and thus biodiversity. They are characterized by a rich biodiversity and different assemblages, not all referable to the coralligenous that distinguish the less disturbed off-shore areas. The contribution of different bioconstructors and a draft list of the main coralligenous taxa recognized are provided. The coralligenous biocoenoses of the Northern Adriatic seem to differ from the Mediterranean ones, mainly for a higher number os suspension feeders and for a lower morpho-functional complexity of the communities. Finally, long-term changes in assemblage composition and species abundances were highlighted.

Infralittoral and circalittoral hard bottom communities in the northern part of the Velebit Channel were investigated. The benthos was collected along six transects: three on Prvić Island (Šilo, Samonjin and Stražica) and three facing them along the Velebit mountain coast (Grmac, Žrnovnica and Kola). Three benthic biocoenoses were noted: the biocoenosis of photophilic algae, precoralligenous facies and a climax of coralligenous biocoenosis, and the biocoenosis of semi-dark caves. A total of 431 taxa were recorded: 60 taxa of algae and 371 taxa of fauna. Along the three coastal transects under Mt Velebit numerous submarine freshwater springs (vruljas) are present. The results were compared using two statistical methods: the application of the Sørensen index of similarity and cluster analysis. The most topographically and geomorphologically similar transects were Šilo and Samonjin, while StraŽica and Žrnovnica were the most distant., Istraživane su bentoske zajednice čvrstog dna u infralitoralu i cirkalitoralu u području sjevernog dijela Velebitskog kanala. Obrađeno je šest profila od čega tri na otoku Prviću (Šilo, Samonjin i Stražica), a tri nasuprot, na kopnu (Grmac, Žrnovnica i Kola). Utvrđene su tri biocenoze: biocenoza fotofilnih alga, pretkoraligenski aspekt i klimaks stadij koraligenske biocenoze te biocenoza polutamnih špilja. Na svih šest istraživanih profila ukupno je utvrđeno 60 biljnih i 371 životinjska svojta. Duž profila podno Velebita nalaze se brojne vrulje. Sørensenovom metodom i klaster-analizom obrađ|eni su rezultati istraživanja. Najveća sličnost u sastavu flore i faune obrađenih biocenoza utvrđena je među profilima Šilo i Samonjin, a najmanja među profilima Stražica i Žrnovnica.

The submarine cave near Vrbnik is 30 m long and it has the shape of an irregular triangular prism. It was formed in upper Cretaceous limestone rocks. The mud and the stone blocks cover the bottom of the cave. The cave was formed under terrestic conditions, probably during Wuerm Glacial age. During the Holocene sea-level rise the cave was submerged. Biocoenological research reveals 23 taxons of macroflora and 112 taxons of macrofauna (Porifera 22, Cnidaria 7, Bivalvia 19, Gastropoda 6, , Cephalopoda 1, Echiura 1, Sipuncula 1, Polychaeta 8, Crustacea 15, Bryozoa 6, Echinodermata 5, Tunicata 4, Pisces 20). The research of Malacostraca revealed 12 species of Decapodes and 2 species of Mysidiacea. Among registered fishes only goby Gammogobius steinitzi is considered to be exclusive cave inhabitant and goby Thorogobius ephippiatus is by far the most numerous fish. From the cave entrance and up to 3 m into the cave a precoralligenous aspect of corallinous biocoenosis was registered. The biocoenosis of semi-dark caves with the predominant Porifera fauna was registered up to 25 m into the cave, while along the last 5 m to the cave end the biocoenosis of caves and ducts in complete darkness is developed, where the Polychaeta are predominant.

Researches of marine flora and fauna of the Rijeka Bay and the whole Kvarner Gulf have been going on for a century and a half. Despite numerous sampling locations in the coastal, open-water and channel zone of the region, the submarine littoral of the Sv. Marko islet remained almost unexplored. Because of the fact, our goal was to describe some biocoenological features of this "blank" area. In the submarine area of the islet of Sv. Marko we have found all together 47 taxa of macroalgae, two species of blue-green algae, 1 phanerogam species and 101 macrofauna species. According to the current data, the benthic communities of Sv. Marko are rich and diverse, but do not differ from other locations of the Rijeka Bay and Kvarner region. An exception is the excessive growth of red algae Polysiphonia spp. that cover comprehensive parts of a bottom surface at some localities. A thick layer of algae obviously reduces the water near- bottom circulation causing anoxic conditions beneath the layer. Such phenomenon was neither recorded during previous researches in the Kvarner nor was noticed in the biocoenologic literature of the eastern Adriatic coast. We believe that there are reasons for establishment of the distinct ruderal biocoenosis of movable stony bottom of infralittoral step. The inclination of the unconsolidated bottom is one of main factors leading to the development of the particular scree community. We consider the present research just as preliminary because of the minimal number of stations which were visited and investigated only once. The well-like submarine cave between stations RI-18 and RI-76 has remained completely uninvestigated.

The present study is based on critically observed data on the taxonomy, ecology and biocoenology of Prosobranchiata from the eastern Adriatic Sea. The data were collected for more than 20 years, during which period a large number of information was obtained for individual gastropod species. The data on some of the recorded gastropods, largely exceed those presented here. The research was carried out in different biotopes of the northern, middle and southern Adriatic, including shallow coastal and deeper open littoral, that is bionomic steps from supralittoral to the bathyal of hard and mobile bottoms. All the authors working in the Adriatic, who could be found in the available literature, were cited for individual species, whereas only more significant authors were reported for the Mediterranean and Atlantic. The paper then presents the species distribution in world seas, vertical and horizontal distributions in the Adriatic and abundance of each species and its relationship to benthic biocoenoses. The reports of other authors were discussed for each individual species. The data from the western Adriatic coast were presented for some species to give as complete account as possible. The most important synonymy is also given. To be sure that the sites of records were authentic only live gastropod specimens were taken into consideration.

Infralittoral and circalittoral hard bottom communities in the northern part of the Velebit Channel were investigated. The benthos was collected along six transects: three on Prvić Island (Šilo, Samonjin, Stražica) and three facing them along the Velebit mountain coast (Grmac, Žrnovnica, Kola). Three benthic biocoenoses were noted: the biocoenosis of photophylic algae, precoralligenous facies and a climax of coralligenous biocoenosis, and the biocoenosis of semi-dark caves. A total of 431 taxa were recorded: 60 taxa of algae and 371 taxa of fauna. Along the three coastal sults were compared using two statistical methods the application of the Sorensen index of similarity and cluster analysis. The most topographically and geomorphologically similar transects were Šilo and Samonjin, while Stražica and Žrnovnica were the most distant.