Search

Natural episodic events, such as gravity flows, submarine landslides, and benthic storms can determine severe modifications in the structure and functioning of deep-sea ecosystems. Here, we report and compare the ecosystem effects produced by dense water formation events that occurred in the Gulf of Lions (NW Mediterranean) and the Aegean Sea (NE Mediterranean). In both regions, the rapid sinking of cold dense waters, driven by regional meteorological forcings, results in important immediate modifications that can be summarised in: (i) increased organic matter content in the deep basin; (ii) diminished benthic abundance; and (iii) changes of benthic biodiversity. At longer time scale the analysis reveals, however, different resilience times in the two regions. The Gulf of Lions is characterized by a very fast (months) recovery whereas the Aegean Sea shows much longer (>5 years) resilience time. New long-term studies are further needed to identify the potential effects that changes in the duration, intensity and frequency of episodic events could have on the structure, biodiversity and functioning of the deep Mediterranean Sea under environmental and climate change scenarios. [ABSTRACT FROM AUTHOR]

While variations in sedimentary organic matter (OM) quantity, biochemical composition and nutritional quality as well as in meiofaunal abundance and assemblage composition at the macro- and mesoscale are relatively well known, information about variations at the microscale is much scarcer. To shed some light on this issue, we tested the null hypothesis by which abundance and composition of the meiofaunal assemblages, and the quantity, biochemical composition and nutritional quality of sedimentary organic matter in coastal shallow environments do not vary within a frame of 1 m2. No significant variation within the frame emerged for OM quantity, nutritional quality, biochemical composition and the abundance of meiofaunal assemblages. On the other hand, the composition of meiofaunal assemblages varied significantly within the frame and exhibited a clear segregation of assemblages farther to the shore, as a likely result of local micro-hydrodynamic conditions. Spatial autocorrelation analysis revealed that lipid and protein sedimentary contents had a random distribution, whereas carbohydrate and biopolymeric C contents and meiofaunal total abundance were characterized by a patchy distribution, with discrete peaks within the sub-frame squares (ca. 0.1 m2). Phytopigments showed a spatial positive autocorrelation distribution, following the micro-hydrodynamic pattern, with patches larger than the sub-frame square, but smaller than the entire one (1 m2). Overall, our results suggest that, within 1 m2 of subtidal sandy sediments, three replicates could be sufficient to assess correctly OM attributes and the abundance of meiofauna, but could be possibly inadequate for assessing meiofaunal assemblages' composition at a finer scale (<1 m²). [ABSTRACT FROM AUTHOR]

Plastic marine debris represents a global threat for the marine environment, having serious consequences for the ocean, the wildlife and the human health. While the plastics distribution, fate, persistence and toxicity mechanisms for the marine fauna have been more studied in the last decade, small efforts have been devoted to identify and characterize marine microbes that colonize plastic and microplastic debris in the ocean, and their potential to degrade plastics. Here we review the knowledge on the microbial biodiversity and degradation mechanisms of marine plastic debris, and present data, based on metagenomic analyses, on the distribution patterns of genes potentially involved in microbially-mediated plastic degradation in coastal locations across the global ocean. Most studies on plastic-colonizing microbes have focused on seawater rather than sediment, with most studies underlining striking differences in composition between assemblages attached to plastic particles and those in the surrounding environment. The diversity of microbes attached to plastic is high, and the core epiplastic microbial assemblages include often hydrocarbon-degrading bacteria, as well as prokaryotic and eukaryotic phototrophs. Several marine microbes have shown to be able to degrade or deteriorate plastic in the laboratory, or to grow on plastic as the only source of carbon, while indirect evidences suggest that microbially-mediated degradation of recalcitrant plastics also occur in the ocean, though at very low rates. Metagenomic analyses show that plastic degradation-related genes are present in microbial assemblages in several coastal ocean sites, with relative abundance related to the magnitude of plastic pollution at each site. Further research is required to study microbial plastic-degraders in the marine ecosystem, to decipher and exploit the potential of microbial consortia to degrade or mineralize plastic compounds, and to better understand the fate and residence times of plastic waste in the ocean. [ABSTRACT FROM AUTHOR]

In view of the general paucity of integrated information on offshore benthic communities in the Adriatic Sea and given the vulnerability of this particular coastal system, microphytobenthos, meiofauna and macrofauna were synoptically investigated in front of the Emilia-Romagna coast (northern Adriatic Sea) in September 2010 and March 2011. As required by the Marine Strategy Framework Directive, which extends its action beyond the territorial waters (within 12 nmi) of the Member States, our findings could help to fill the gap of knowledge on the environmental status in offshore areas since the study was carried out also at >12 nmi from the coastline. In fact, sediment samples for the analysis of the benthic communities were collected from a 10-point-station grid that covered an area of about 400 km2 with water depths ranging from 13 to 50 m. The variability of the sediment grain size and other chemical variables in the sediment suggests the presence of two distinct environmental contexts that enhance the proliferation of different benthic communities. At the inshore stations (depth <20 m) the higher sand percentages and the maxima of dissolved inorganic nitrogen concentrations indicated the presence of hydrodynamic perturbations and the influence of nutrient loads of terrestrial origin. Inshore, both meio- and macrofaunal communities were poorly structured and dominated by relatively more opportunistic taxa, such as nematodes and the bivalve Corbula gibba. Offshore stations (depth >20 m) had muddier sediments, which likely exerted a greater retention of sediment-bound organic matter. These conditions seemed to favour benthic deposit feeders like meio- and macrofaunal annelids. Surprisingly, a conspicuous microphytobenthic community, mainly represented by the diatom Paralia sulcata, has been observed even at remarkable depths (~50 m) opening new questions regarding the role of these organisms in dim-light conditions. Although the investigated benthic communities were, to some extent, moderately influenced by multiple stressors, the co-existence of sensitive taxa (such as meiofaunal copepods and the amphipod Ampelisca spp.) with opportunistic ones (i.e., C. gibba) suggests that the benthic domain in the investigated area is not severely impacted. [ABSTRACT FROM AUTHOR]

Quantitative information on the spatial distribution of meiofaunal abundance, biomass and biodiversity (as richness of higher taxa) is summarised from 476 sites of the deep- Mediterranean Sea, at depths ranging from ca. 200 to 4617 m. Meiofaunal abundance (465 ± 31 and 306 ± 24 ind 10 cm-2 at 200-1000 and 1000-2000 m depth intervals) and biomass (125 ± 16 and 119 ± 20 µgC 10 cm-2 at 200-1000 and 1000-2000 m depth intervals) in the bathyal sediments of the Mediterranean Sea are similar to those reported in oceans worldwide but at much higher depths (abyssal or hadal). Meiofaunal abundance, biomass and richness of taxa displayed a common decreasing bathymetric pattern, but showed a steeper negative slope than in other oceanic regions. Latitudinal and longitudinal gradients revealed idiosyncratic patterns when different basins (Western, Central and Eastern) and habitats (open slope, canyon, deep basin and trench) were considered. The results of the non parametric multivariate multiple regression analyses revealed that, conversely to what expected, depth is not the key factor in explaining the variance of meiofaunal assemblages living down to 2000 m depth. The quality and quantity of food sources explained a larger fraction of the variance of meiofaunal variables (47, 25 and 33% for abundance, biomass and diversity, respectively) and the importance of food sources increased with increasing depth. However, most of the variance remains unexplained suggesting that other factors (such as episodic events, deep currents, other unexplored yet environmental characteristics) can act a key role in driving the observed meiofaunal spatial patterns. The analysis of rare taxa (on a data set of 183 samples), suggested that differences in the meiofaunal community were evident when dominating taxa (nematodes, copepods and polychaetes) were excluded. We report the presence of rare taxa exclusively present in open slope (amphipods) and canyon (cnidarians and decapod larvae) systems, whereas others are exclusively found in one of the two basins (e.g. gastrotrichs in the Western basin and amphipods and gastropods in the Eastern basin). The apparent preference of some rare taxa for a specific habitat or basin could have important implications for the identification of the hot spots of benthic diversity, for identifying the connectivity among systems and for an appropriate management of deep-sea habitats in the Mediterranean Sea. [ABSTRACT FROM AUTHOR]