Nunzio Penna,¹ Nives Kovač,² Fabio Ricci,³ Antonella Penna,⁴ Samuela Capellacci³ and
Jadran Faganeli²

¹ Chair of Chemical Oceanography, University of Urbino, Loc. Crocicchia, 61029 Urbino (PU) Italy
² Marine Biological Station, National Institute of Biology, Fornače 41, 6330 Piran, Slovenia
³ Center of Environmental Biology, University of Urbino, V.le Trieste, 296, 61100 Pesaro (PU), Italy
⁴ Istitute of Environmental Ecology and Biology, University of Urbino, V.le Trieste, 296, 61100 Pesaro (PU), Italy
* Corresponding author: E-mail: jadran.faganeli@mbss.org

Abstract
Total dissolved carbohydrates and their monosaccharide and polysaccharide fractions were studied at a fixed sampling point in the northern Adriatic Sea off Pesaro, Italy, in 2002, 2003, and 2004 which were characterized by the presence of macroaggregates, and in 2001 and 2005 when the macroaggregates were absent. During the presence of macroaggregates in 2004, the study was extended to the southern part of the Gulf of Trieste, Slovenia. In parallel, phytoplankton biomass determined from chlorophyll a concentration, and nitrogen and phosphorus nutrients were tracked. The concentrations of total dissolved carbohydrates and, above all, dissolved polysaccharides were higher in late spring and early summer before and during the mucilage appearance. Conversely, the concentrations of dissolved monosaccharides remained nearly constant throughout the study period. In addition to higher polysaccharide concentration, other hydrological, chemical and biological factors seem also important for macroaggregate formation in the northern Adriatic Sea. Among them, the DIN/PO₄ ^3– ratios, regularly increasing in spring due to phytoplankton use of nitrate and phosphate, could be indicative of macroaggregates appearance since they were lower in 2001 and 2005 while during the presence of mucilage in 2002, 2003 and 2004 they markedly increased.

Keywords: Dissolved carbohydrates, mucilage, nutrients, phytoplankton, northern Adriatic Sea