Scienze e Tecnologie

A study on the meiobenthic nematode assemblages from three Italian Marine Protected Areas (Miramare, Adriatic Sea; Porto Cesareo, Ionian Sea; and Capo Caccia, Western Mediterranean Sea) was carried out at three different depth ranges from the low intertidal to the shallow subtidal. Nematode community composition was analysed at the genus level, and diversity and taxonomic distinctness were studied to detect possible differences among the MPAs and between intertidal and shallow subtidal zones. There were differences in granulometric variables between sampling depths: medium and coarse fractions were often dominant in the sites at the low intertidal and shallow subtidal, while very shallow subtidal sites were characterised by fine and very fine sand. Nematode densities and diversities were generally high in all sampling areas. Nematode communities changed when different depths were compared. This was due to a decrease in deposit-feeding nematodes coupled with a higher abundance of predators and epigrowth feeders with increasing depths, from the low intertidal to the shallow subtidal. The shallow subtidal is characterised by the presence of a stout nematode community (Length/Width ratio <15) dominated by Epsilonematidae (39%), Desmoscolecidae (16%) and Selachinematidae (9%). The high dominance of the epsilonematids is probably due to the occurrence of coarse sediments. Our study also reveals a possible relationship between body proportions and feeding groups. Changes in depth and sand grain size do not seem to cause drastic variations of diversity. Both + and + seem to be more sensitive than other diversity indices in discriminating among different sites, as a consequence of different environmental physical features. The concept of isocommunities might explain the similarities found in the three Italian Marine Protected Areas nematode assemblages; in fact, the same dominant families and genera were recorded in geographically spaced sites at similar depth ranges.

Taxonomic distinctness has been applied successfully for the exploration of biodiversity patterns, yet its relevance in environmental impact assessment is far from being unquestioned. In this study, we assessed the potential of taxonomic distinctness to discern perturbed and unperturbed sites by analysing Mediterranean nematode assemblages. Geographic and habitat-related effects on the performance of the index were also explored. Above all, our findings do not corroborate the conjecture that taxonomic distinctness could be largely unaffected by natural variability, habitat features, and biogeographic context, casting doubts on potential generalization concerning its application as an indicator of environmental stress. Taxonomic distinctness represents an excellent metric to identifying taxonomic properties of ecological systems but, as for other ecological indices, it should be viewed as a complementary tool in environmental impact assessment, due to its sensitiveness to specific environmental features of systems being investigated.

The existence of deep red coral (Corallium rubrum) banks in the gulfs of Naples and Salerno (South Tyrrhenian Sea, Mediterranean Sea) is well known in historical records due to the heavy coral harvesting that occurred during the 19th and 20th centuries, by both trawling gears and scuba diving. In 2010 and 2012, during two Remotely Operated Vehicle (ROV) surveys on board of the Research Vessel (R/V) Astrea, red coral banks were detected in 16 of the 25 visited localities, between 45 and 150 m depth. Seven of these banks, located in the inner part of the Gulf of Naples, were already explored in 1918 by a scientific survey reporting the occurrence of red coral. Healthy populations (densities > 90 colonies m −2 ) were present only around the coasts of the Phlegrean Islands (Ischia and Procida Islands). Very low densities (< 5 colonies m −2 ) or the absence of coral were recorded in all other sites of the Gulf of Naples (including all historical re-visited banks), and a variable percentage of dead colonies was observed. This evidence suggests a huge state of stress likely favoured by the hydrodynamic conditions in the Gulf, enhancing water pollution and sedimentation rate. Finally, the documented high fishing pressure plays a major role in the hard-bottom communities' degradation. A recent mass mortality episode was also recorded along the Amalfi coast, around Li Galli Islands (Gulf of Salerno), at a depth range between 80 and 100 m, where the mortality affected 80% of the largest colonies, estimated to be around 70 years old. Several possible reasons for this mortality have been hypothesised, such as the formation of local down-welling currents inducing an unusual drop of the thermocline, or sudden warm water emissions (sulphur springs) in an area characterised by important volcanic activities, or local landslides generating turbidity currents along the steep slopes.

In this paper we have explored for the first time the biodiversity pattern of the meiobenthic assemblage in a Blue Hole of the Maldivian Archipelago. The cave is characterised by a marked change of the chemical water parameters below 50 m of depth, with a relevant increase in hydrogen sulfide, carbon dioxide, and sulfates (H 2 S, CO 2 and SO 4 2-). Thus, three stations were selected above and two below the chemo-thermocline in order to test the possible effects of the chemical variations on the meiobenthos. The difficulty of adaptation to these environmental conditions is clearly suggested by the presence of only a few dominant meiobenthic taxa in the bottom of the cave. However, meiobenthic organisms seemed more resistant than macrobenthos, which disappeared completely below this depth. The nematode assemblage was mainly represented by Xyalidae, Desmodoridae, Comesomatidae and Linhomoeidae. A high level of confinement of nematode genera at the different depths has been documented. In the upper part, their structure and biodiversity were comparable to those of the Maldivian subtidal habitats characterised by fine coralline sediments, while a notable dominance was detected in the bottom. The Blue Hole features also influenced the functional traits of the nematode assemblage with a documented increasing number of general opportunists and decrease of Maturity Index. The dominance of non-selective deposit feeders supports the hypothesis of a high amount of organic matter accumulated on the sea bottom of the cave.

Fourteen years after the first observation of Cuulerpa tuxifolia (Valh) C. Agardh in the northwestern Mediterranean Sea, this green alga of tropical origin is now present in five countries (Spain, France, Monaco, Italy and Croatia). By the end of 1997, more than 46 km2, at depths of between 0 and 50 m, were found to be affected by this expansion. A standardization of the cartographic procedure is proposed here. Such a standardization is necessary to compare maps produced by various organizations from different countries. For a given independent station, it is based on the definition of three levels of colonization: -Level I refers to a station where one or several colonies less than 100 m apart cover a total surface area inferior to 1000 m2; -Level II refers to a station where several colonies less than 250 m apart totally cover more than 1000 m2 with fragments and small colonies dispersed over a surface area inferior to 10 ha; -Level III is attained when several large colonies are dispersed over a surface area superior to 10 ha, with a total covered surface of more than 1000 m2, impossible to map with precision due to its size.

The management of the red coral, Corallium rubrum (L.), is an international issue still lacking of an effective solution in the Mediterranean Sea. The main goal of this research was the evaluation of the ROV efficiency as a monitoring non-destructive tool in studies concerning the conservation status of the deep red coral populations (living under 50 m depth). Both Ligurian Sea and Tuscan Archipelago are considered among the most important Italian historical sites of the red coral professional harvesting. Fishing effort in these areas is now decreased (in Liguria is virtually ceased) due to the drastic reduction of colonies of commercial size and thanks to conservation laws. Today, the protection of this natural resource has been directed mainly to coastal, shallow-water populations (living between 20 and 40 m depth), while the deeper banks, the main target of professional harvesting by technical scuba divers, still need dedicated management plans. ROV explorations allowed the ident...