Silvia Bianchelli

Eutrophication enhances organic C inputs to the sea bottom, so that the quantity and biochemical composition of sedimentary organic matter are expected to change under different trophic status conditions. In turn, changes in the trophic status are often associated with shifts in the abundance and community structure of the benthos. We investigated the quantity and biochemical composition (protein, carbohydrate, lipid and phytopigment) of sedimentary organic matter together with abundance and community structure of meiofauna in two regions of the Mediterranean Sea characterized by different levels of primary productivity. At each region, five transects were randomly selected along the coastline. At each transect, three stations located at increasing distance from the shore and different water depth were investigated. Uni- and multivariate analyses of variance revealed that the quantity and biochemical composition of sediment organic matter displayed the most relevant differences between stations, suggesting their potential use as descriptor of the benthic trophic state at the small spatial scale (i.e. <2 km). The correlation analyses, corroborated by nMDS dispersion plots and cluster analyses highlighted that the biopolymeric C content of the sediment and the algal fraction of sediment organic matter were inversely related and able to discriminate the trophic status at the scale of region, transect and station. Uni- and multivariate analyses on meiofaunal assemblages revealed that differences at different spatial scales were less evident in terms of abundance and richness of meiofaunal taxa but were more evident in terms of taxonomic composition. Furthermore, these differences were enhanced when the analyses were restricted using the meiofaunal rare taxa (i.e. those taxa representing <1% of the total meiofaunal abundance) as an input. The results of the multivariate multiple regression analyses revealed that the taxonomic composition of meiofaunal assemblages was driven mostly by protein, biopolymeric C and chlorophyll-a concentrations but also by the algal fraction of biopolymeric C. We conclude that, the study of the quantity and biochemical composition of sediment organic matter coupled with an analysis of the rare meiofaunal taxa allows an ecosystem-oriented assessment of the trophic status of marine benthic environments.

We describe the quantitative and compositional (phytopigment, protein, carbohydrate and lipid) patterns of sedimentary organic matter along bathymetric gradients in seven submarine canyons and adjacent open slopes located at four European regions: one along the NE Atlantic and three along the Mediterranean continental margins. The investigated areas are distributed along a putative longitudinal gradient of decreasing primary production from the Portuguese (northeastern Atlantic Ocean), to the Catalan (western Mediterranean Sea), Southern Adriatic (central Mediterranean Sea) and Southern Cretan (eastern Mediterranean Sea) margins. Sediment concentrations of organic matter differed significantly between the Portuguese margin and the Mediterranean regions and also from one study area to the other within the Mediterranean Sea. Differences in quantity and composition of sediment organic matter between canyons and open slopes were limited and significant only in the eutrophic Portuguese margin, where the differences were as large as those observed between regions (i.e. at the mesoscale). These results suggest that the overall trophic status of deep margin sediments is controlled mostly by the primary productivity of the overlying waters rather than by the local topography. Moreover, we also report that the quantity and nutritional quality of sediment organic matter in canyons and adjacent open slopes do not show any consistent depth-related pattern. Only the Nazaré and Cascais canyons in the Portuguese margin, at depths deeper than 500 m, displayed a significant accumulation of labile organic matter. The results of our study underline the need of further investigations of deep margins through sampling strategies accounting for adequate temporal and spatial scales of variability.

The Descriptor 5 (Eutrophication) of the EU Marine Strategy Framework Directive aims at preventing the negative effects of eutrophication. However, in coastal systems all indicators based on water column parameters fail in identifying the trophic status and its effects on biodiversity and ecosystem functioning. We investigated benthic trophic status, in terms of sedimentary organic matter quantity, composition and quality, along with meiofaunal abundance, richness of taxa and community composition in three coastal sites (N Adriatic Sea) affected by different levels of anthropogenic stressors. We show that, on the basis of organic matter quantity and composition, the investigated areas can be classified from oligo-to mesotrophic, whereas using meiofauna as a descriptor, their environmental quality ranged from sufficient to moderately impacted. Our results show that the benthic trophic status based on organic matter variables, is not sufficient to provide a sound assessment of the environmental quality in marine coastal ecosystems. However, data reported here indicate that the integration of the meiofaunal variable allows providing robust assessments of the marine environmental status.

... identification of these sys-tems as hot spots of deep-sea biodiversity (de Boveé ... Meiofauna are the numerically dominant metazoan components of the deep-sea benthos (Vincx ... Nematodes are the most abundant metazoan meiofaunal taxon, and their dominance increases with ...

To identify the relationships between the abundance and biodiversity of deep-sea meiofauna and their food resources in the Tyrrhenian Sea (Mediterranean Sea), we have investigated the quantity and biochemical composition of sediment organic matter, the ...

... and ecology of marine organisms living in the largest biome on Earth (ie deep oceans at &amp;gt;1000 m depth) are still scarce, being limited in space and fragmentary in time 33. Danovaro, R., Dell&amp;#x27;Anno, A., Fabiano, M., Pusceddu, A ... Hopkins, CCE, Sargent, JR and Nilssen, EM 1993. ...