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Spatial and temporal variability of carbohydrates in the northern Adriatic - A possible link to mucilage events

Large-scale mucilage events in the northern Adriatic have become more frequent during the last few decades. Since carbohydrates (CHO) comprise the major constituents of the Adriatic mucilage, studying their seasonal and spatial patterns is one of the key prerequisites for the understanding of this phenomenon. This paper reports on the distribution of particulate (PTCHO) and dissolved carbohydrates (DTCHO) in the period from June 1999 to July 2002, with a special emphasis on the summer mucilage events. A particular attention was paid to the relationship between the phytoplankton crop as reflected by photosynthetic pigments and carbohydrate levels in different seasons. The concentration of PTCHO varied in a very wide range (1-72 μ mol C/l). Their seasonal distribution revealed that enhanced levels of PTCHO occurred only in the surface layer (0-5 m) and were associated with major phytoplankton blooms. However, the main pool of CHO was in the dissolved fraction, comprising on average 84&plusmn ; ; ; ; ; ; ; 10 % of the total CHO. In contrast to PTCHO, there was no seasonal coincidence between the enhanced phytoplankton biomass and concentrations of DTCHO. In fact, the concentration of DTCHO showed a marked increase during the stratification period, when the phytoplankton biomass remained relatively low. Nevertheless, the concentration of DTCHO in the productive surface layer, influenced by the Po River discharges, was significantly higher than that in the deeper layers. The detailed vertical distribution of carbohydrates indicated that phytoplankton populations in the bottom layer possess a rather modest potential as a source of CHO. The spatial distribution in the surface layer along the transect Rovinj - Po River mouth revealed only a moderate increase of the total CHO concentration in the more eutrophic western part of the basin. The average summer concentration of CHO in the investigated period (34 μ mol C/l) was higher than those in the normal years (1994 and 1998) and rather similar to that during the 1997 mucilage event.

carbohydrates; mucilage; northern Adriatic; phytoplankton; photosynthetic pigments

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