The organic matrix of pelagic mucilaginous aggregates in the Tyrrhenian Sea (Mediterranean Sea) Michele Giani a, c , Paola Sist b , Daniela Berto c , Gian Paolo Serrazanetti d , Vittoria Ventrella d , Ranieri Urbani b, ⁎ a Istituto Nazionale di Oceanografia e Geofisica Sperimentale, via Piccard 54, 34151 Trieste, Italy b Dipartimento di Scienze della Vita, University of Trieste, via Giorgieri 1, 34127 Trieste, Italy c Istituto Superiore per la Protezione e la Ricerca Ambientale, Loc. Brontolo, 30015 Chioggia, Italy d Dipartimento di Scienze Mediche Veterinarie, University of Bologna, Via Tolara di Sopra 50, Ozzano dell'Emilia, Bologna, Italy abstract article info Article history: Received 4 August 2011 Received in revised form 28 December 2011 Accepted 5 January 2012 Available online 14 January 2012 Keywords: Mediterranean Sea Mucilage Monosaccharides Fatty acids Sterols Humic acids In the last fifteen years the presence and distribution of large aggregates in the Mediterranean Sea have begun to be studied suggesting that these particles could play a relevant role in the carbon biogeochemistry of the basin. However the massive formation is a sporadic event and it is often difficult to detect. During the autumn of 2000 high densities of mucilage aggregates were observed in the major part of the coastal zone of the Tyrrhenian Sea (western Mediterranean Sea). The chemical composition and origin of these aggregates were evaluated. The carbohydrates, proteins, lipids and the humic and fulvic acid fractions constitute 45– 68% of the organic carbon (OC). Marine origin was suggested by UV spectra and C/N ratios of humic sub- stances extracted from mucilage samples. The polysaccharide component was isolated and purified by extraction of four fractions of different solubility and the saccharide carbon percentage ranged from 13 to 20% of the OC. By comparison the qualitative and quantitative monosaccharide, fatty acid and sterol compo- sitions were very similar to those obtained from Adriatic pelagic mucilages, while on the other hand the re- sults showed remarkable differences in comparison to benthic aggregates. Scanning electron microscopy (SEM) on native samples showed a complex morphology with the presence of fibrillar structures forming a highly branched tri-dimensional network similar to those found in Adriatic pelagic samples. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Mucilages are produced at a microscale in the marine environ- ment by many autotrophic (macroalgae, phytoplankton) and hetero- trophic organisms (bacteria, corals, zooplankton) (Decho and Herndl, 1995 and references therein); however, the aggregation of mucilagi- nous matter at the basin scale is an episodic event that takes place re- currently in only a few specific areas worldwide, including New Zealand (Mackenzie et al., 2002) and the Adriatic sea (e.g. Precali et al., 2005). In some areas, such as in the North Sea, the aggregates are quite different from mucilaginous aggregates and have character- istics of foams. Their formation has been attributed to specific organ- isms, including Phaeocystis pouchetii (e.g., Lancelot et al., 1995). The massive formation of mucilaginous aggregates has been ob- served in different areas of the Mediterranean Sea. The presence of mucilaginous aggregates has been recorded since the 19th century (Hauk, 1872); however, since the end of the 1980s, the number of ob- servations has increased. The presence of mucilaginous aggregates has been described in the Adriatic Sea (Giani et al., 1992; Herndl, 1992; Precali et al., 2005), in the Tyrrhenian Sea (Calvo et al., 1995; Innamorati, 1995; Rinaldi et al., 1995), along the southern coast of Sic- ily, in the Ionian Sea (Calvo et al., 1995), and in Greece (Gotsis- Skretas, 1995; Metaxatos et al., 2003). More recently, mucilaginous aggregates were observed in the northwestern Mediterranean Sea (Sampedro et al., 2007); Aegean Sea (Aktan and Topaloğlu, 2011) and Marmara Sea (Aktan et al., 2008; Balkis et al., 2010; Tüfekçi et al., 2010). Sometimes aggregates of completely different origin are recorded under the generic term of “mucilage”, as was the case during the summer of 1991 when benthic and pelagic mucilage were concur- rent in the Tyrrhenian Sea. Benthic and pelagic mucilage can be con- founded or grouped together, although their origin and mechanism of formation are completely different (Sartoni et al., 2008). The aggrega- tion of phytoplanktonic cell into large (>500 μm) aggregates has been shown to be a relevant feature of the world's oceans (Alldredge and Silver, 1988) and, more recently, of the Mediterranean Sea, where up to 30% of the total particulate matter can be aggregated into large (>150 μm) particles (Stemmann et al., 2002).The first recent record of a pelagic mucilage formation at the basin scale in the Tyrrhenian Sea oc- curred in 1991; during this year, the formation of aggregates was ob- served first in the southern Tyrrhenian Sea in the late spring–summer and then during the summer in the central and northern Tyrrhenian Sea. In some areas, such as the Salerno gulf, the trawling nets can Marine Chemistry 132–133 (2012) 83–94 ⁎ Corresponding author at: Department of Life Sciences, University of Trieste, via Giorgieri 1, 34127 Trieste, Italy. Tel.: + 39 0405583976; fax: + 39 0405583691. E-mail address: rurbani@units.it (R. Urbani). 0304-4203/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.marchem.2012.01.002 Contents lists available at SciVerse ScienceDirect Marine Chemistry journal homepage: www.elsevier.com/locate/marchem