Gianfranco D'Onghia

Deep-Sea Biodiversity in the Mediterranean Sea: The Known, the Unknown, and the Unknowable

Deep-sea ecosystems represent the largest biome of the global biosphere, but knowledge of their biodiversity is still scant. The Mediterranean basin has been proposed as a hot spot of terrestrial and coastal marine biodiversity but has been supposed to be impoverished of deep-sea species richness. We summarized all available information on benthic biodiversity (Prokaryotes, Foraminifera, Meiofauna, Macrofauna, and Megafauna) in different deep-sea ecosystems of the Mediterranean Sea (200 to more than 4,000 m depth), including open slopes, deep basins, canyons, cold seeps, seamounts, deep-water corals and deep-hypersaline anoxic basins and analyzed overall longitudinal and bathymetric patterns. We show that in contrast to what was expected from the sharp decrease in organic carbon fluxes and reduced faunal abundance, the deep-sea biodiversity of both the eastern and the western basins of the Mediterranean Sea is similarly high. All of the biodiversity components, except Bacteria and Archaea, displayed a decreasing pattern with increasing water depth, but to a different extent for each component. Unlike patterns observed for faunal abundance, highest negative values of the slopes of the biodiversity patterns were observed for Meiofauna, followed by Macrofauna and Megafauna. Comparison of the biodiversity associated with open slopes, deep basins, canyons, and deep-water corals showed that the deep basins were the least diverse. Rarefaction curves allowed us to estimate the expected number of species for each benthic component in different bathymetric ranges. A large fraction of exclusive species was associated with each specific habitat or ecosystem. Thus, each deep-sea ecosystem contributes significantly to overall biodiversity. From theoretical extrapolations we estimate that the overall deep-sea Mediterranean biodiversity (excluding prokaryotes) reaches approximately 2805 species of which about 66% is still undiscovered. Among the biotic components investigated (Prokaryotes excluded), most of the unknown species are within the phylum Nematoda, followed by Foraminifera, but an important fraction of macrofaunal and megafaunal species also remains unknown. Data reported here provide new insights into the patterns of biodiversity in the deep-sea Mediterranean and new clues for future investigations aimed at identifying the factors controlling and threatening deep-sea biodiversity.

Biodiversity of the white coral reefs in the Ionian Sea (Central Mediterranean)

Three surveys were carried out off Cape Santa Maria di Leuca (Southern Italy). Samples were taken using an ‘ingegno’, trawl net and traps at 630–1100 m depth. The white coral biocoenosis in this area of the Ionian Sea consists of living corals mainly represented by the framework builders Lophelia pertusa and Madrepora oculata. The solitary corals Desmophyllum cristagalli and Stenocyathus vermiformis were also obtained alive. The polychaete Eunice norvegica is another characteristic species. A list of 58 species were compiled, indicating the Atlantic character of this biocoenosis and confirming Mediterranean biodiversity to be lower than that of ocean.

Demersal fish assemblages from the bathyal grounds of the Ionian Sea (middle‐eastern Mediterranean)

Abstract Data collected during four trawl surveys conducted in the Ionian Sea were used to describe the structure and spatial distribution of the demersal assemblages (fishes, crustaceans and cephalopods) on the bathyal grounds. Samples were taken from depths of 200 to 700 m during spring and autumn of 1994 and 1995. Classification and ordination of the demersal communities were conducted with cluster and correspondence analyses, respectively. Speciesasswere associated with depth. Two faunal assemblages were identified in the uppermost (about 200–400 m) and in the deepest (about 400–700 m) investigated bottoms. The former was characterized by greater abundance and biomass of mostly hake, blue whiting, rose shrimp and Norway lobster. The latter was represented by deep‐water sharks, macrourids and deep‐water decapod crustaceans. On the upper slope, two main geographic areas (one north of the Taranto valley the other south) were distinguished in the correspondence analysis.

Comparing Deep-Sea Fish Fauna between Coral and Non-Coral “Megahabitats” in the Santa Maria di Leuca Cold-Water Coral Province (Mediterranean Sea)

Two experimental longline surveys were carried out in the Santa Maria di Leuca (SML) cold-water coral province (Mediterranean Sea) during May–June and September–October 2010 to investigate the effect of corals on fish assemblages. Two types of “megahabitat” characterized by the virtual absence of fishing were explored. One was characterized by complex topography including mesohabitats with carbonate mounds and corals. The other type of megahabitat, although characterized by complex topographic features, lacks carbonate mounds and corals. The fishing vessel was equipped with a 3,000 m monofilament longline with 500 hooks and snoods of 2.5 m in length. A total of 9 hauls, using about 4,500 hooks, were carried out both in the coral megahabitat and in the non-coral megahabitat during each survey. The fish Leucoraja fullonica and Pteroplatytrygon violacea represent new records for the SML coral province. The coral by-catch was only obtained in the coral megahabitat in about 55% of the stations investigated in both surveys. The total catches and the abundance indices of several species were comparable between the two habitat typologies. The species contributing most to the dissimilarity between the two megahabitat fish assemblages were Pagellus bogaraveo, Galeus melastomus, Etmopterus spinax and Helicolenus dactylopterus for density and P. bogaraveo, Conger conger, Polyprion americanus and G. melastomus for biomass. P. bogaraveo was exclusively collected in the coral megahabitat, whereas C. conger, H. dactylopterus and P. americanus were found with greater abundance in the coral than in the non-coral megahabitat. Differences in the sizes between the two megahabitats were detected in E. spinax, G. melastomus, C. conger and H. dactylopterus. Although these differences most probably related to the presence-absence of corals, both megahabitats investigated play the role of attraction-refuge for deep-sea fish fauna, confirming the important role of the whole SML coral province as a refuge area from fishing.

The demersal faunal assemblage of the north-western Ionian Sea (central Mediterranean): current knowledge and perspectives

Data reported in this article were collected in the context of several trawl surveys carried out in the north-western Ionian Sea in the last 25 years. An overview of the available information on the demersal resources in the area and an historical analysis at population and community levels is reported with the aim of identifying eventual significant changes over time. During the study period 1985–2006, a total of 365 species (41 cephalopods, 76 crustaceans, 33 chondroichthyes and 215 osteichthyes) were collected in the investigated area from 10 to 4000 m, updating the faunal lists of this area with 18 new records and one alien species for the Mediterranean. An increase in the species richness was observed throughout the study period. The historical analysis showed a low abundance of chondroichthyes and significant increases over time for cephalopods, crustaceans and osteichthyes during the study period 1985–2006. An increasing trend in density over time was also detected for some target species (Illex coindetii and Nephrops norvegicus) and an inverse significant correlation with the fishing effort was also shown. Nevertheless, a significant decrease in the median lengths over time was depicted for N. norvegicus and Parapenaeus longirostris. A decreasing trend in the total mortality (Z) and exploitation rates (E) with time was only observed for Mullus barbatus. An overexploitation condition was shown by P. longirostris and Merluccius merluccius during time while a moderate overexploitation was detected for M. barbatus and Aristaeomorpha foliacea over time. A state of almost equilibrium and an optimal exploitation were observed for N. norvegicus and Aristeus antennatus, respectively. The authors give rise to discussion on the fishing effort-exploitation rate-recruitment process to explain the trends shown in the north-western Ionian Sea.

Occurrence of Musculista senhousia (Mollusca: Bivalvia) in the Taranto seas (eastern-central Mediterranean Sea)

Department of Zoology,Via Orabona, 4,70125 Bari, Italy*Corresponding author, e-mail: f.mastrototaro@biologia.uniba.itThe ¢rst record of Musculista senhousia in theTaranto seas (eastern-central Mediterranean Sea) is reported.The species wasmostly found on bottoms with pleustophytic algal felt where densities up to 3800 specimens per square metre were estimated.The sizes in the sampled population ranged from 5.16 to 30.59mm. Two main modal components were detected around11.67 0.67mm and 18.00 2.38mm.Musculista senhousia (Benson in Cantor,1842) is a small musselwidespread in several regions of the earth from the Asian conti-nent (locus tipicus) to the western coast of the USA, to the NewZealand and Australian coasts, along the Israel coast to the RedSea, oi the islands of Zanzibar and Madagascar as well as inIndo-China and Japan (Lazzari & Rinaldi, 1994). This smallmussel was recorded as an immigrant species for the ¢rst time inthe western Mediterranean along the French coast (Hoenselaar& Hoenselaar,1989). Successively it was recorded in Italy, in theAdriatic Sea, in the brackish lagoons of Ravenna (Lazzari R Mistri et al., 2001) and in theTyrrhenian Sea inthe Gulf of Olbia (Savarino & Turolla, 2000).The ¢rst occurrence of M. senhousia in theTaranto seas (north-western Ionian Sea) is reported in this note.The town of Taranto is located on the coast of the north-western Ionian Sea (eastern-central Mediterranean). To thesouth-west it overlooks the open sea in the Mar Grande basinand north-eastwards the basin of the Mar Piccolo which ismade up of two smaller inlets (I and II seno) (Figure 1). TheMar Piccolo covers an area of 20.72km

The bathyal benthopelagic fauna in the north-western Ionian Sea: structure, patterns and interactions

The main knowledge acquired on the structure, patterns and interactions in the bathyal benthopelagic fauna in the north-western Ionian Sea is summarised in this article. Using faunal sampling along a depth range between 200 and 4000 m, a total of 41 cephalopods, 64 crustaceans and 183 fishes have been collected. Some are new findings for the study area and for many of the species the bathymetric distribution has been updated. Distinct faunal assemblages related to the upper slope (400–800 m), middle slope (800–1200 m) and lower slope (>1200 m) were identified using Abundance Biomass Comparison curves. Species abundance decreases across the bathymetric gradient, whereas the biomass increases to ∼1000 m and then decreases again. Beyond this bathymetry, species richness, evenness and diversity index decrease with depth. The distribution pattern ‘bigger–deeper’ was observed in some species and ‘smaller–deeper’ in others. Roccella canyon and the Santa Maria di Leuca coral bank were investigated in relation to the distribution of fauna, highlighting migration phenomena in the former and a refuge effect in the latter. The effects of hydrographic conditions and fishing were also examined for the deep-water commercial shrimps Aristaeomorpha foliacea and Aristeus antennatus.

Mapping of the benthic communities in the Taranto seas using side-scan sonar and an underwater video camera

Side-scan sonar and underwater video camera records as well as dredging samples were used to map the bottom morphology and biocoenoses in the Taranto seas. A 1:20,000 scale chart has been produced with all the data recorded. Most of the study area consists of biocoenoses affected by the anthropogenic activities of the town of Taranto. Some native broadly tolerant species seem to benefit from these activities and become increasingly dominant. Environmental modifications also seem to favour the settlement of exotic species.

Benthic diversity of the soft bottoms in a semi-enclosed basin of the Mediterranean Sea

The benthic diversity of the soft bottoms in the Taranto Seas (Mar Grande and Mar Piccolo) (eastern-central Mediterranean Sea) was studied during July 2002. Quantitative samples were taken using a Van Veen grab and granulometric analysis of the sediment was carried out. A total of 131 species were identified. Molluscs and annelids made up 77% of the species and 87% of the individual number. Data from these two groups were used for hierarchical clustering and multidimensional scaling. The diversity was calculated using the rarefaction method. Two main benthic species assemblages were identified. The first corresponded to the stations characterized by pelitic sediment and located in the Mar Piccolo, the second was made up by the stations with pelite with increasing percentages of sand and distributed in the Mar Grande. The first assemblage consisted of species that usually live on muddy bottoms rich in organic matter; the second consisted of a greater number of species, usually occurring on different types of bottoms. Diversity was found to be higher in the Mar Grande than in the Mar Piccolo, indicating that physico-chemical alterations of the environment probably play a leading role in controlling community structure.

Spawning and recruitment of Phycis blennoides (Phycidae) from the north‐western Ionian Sea (middle‐eastern Mediterranean)

Abstract Specimens of Phycis blennoides were collected in the Ionian Sea by means of trawl surveys from August 1993 to July 1995. Ripe females and mature males were caught during November through January and between August and March, respectively. Recruitment, represented by individuals of 6–8 cm total length modal group, took place during March at depths between 200 and 600 m. Modal progression analysis of juveniles indicated a growth rate of about 1 cm/month during the first year. Otoliths were examined from juveniles. A transition zone was generally observed in the otolith nucleus. Females and males had mean size of 15.6 and 15.4 cm TL, respectively, during the first year, while during the 2nd year individuals attained a mean size of 20.7 and 20.3 cm TL, respectively. The fastest growth occurred during the spring and summer seasons.