engleski

Transparent exopolymer particles (TEP) in the northern Adriatic

Sticky polysaccharide microaggregates, called transparent exopolymeric particles (TEP), are abundant in marine ecosystems (103-108 L-1) and largely responsible for aggregation processes, like "marine snow" formation and diatoms' aggregation. Their important role in the periodic mucilage events in the northern Adriatic has also been hypothesized. During these summer events surface and subsurface layers of mucilaginous matter ("false bottom") kilometres long are formed and aggregates of several meters in length appear in the water column, affecting the ecosystem functioning as well as fisheries and tourism economy. A three years study of TEP distribution and its relations to oceanographic and biological parameters was conducted to verify its role in the mucilage phenomenon. Samples were collected approximately monthly in the period 1999 to 2002 at nine stations, five depths each, along the transect Rovinj (Croatia) - Po River Delta (Italy). TEP concentrations were measured by the Alcian-blue colorimetric method, using Xanthan Gum as an equivalent. In order to explain the mechanism of TEP formation, TEP concentration was correlated with chlorophyll a and pheophytin concentration, bacterial abundance and salinity. Obtained TEP concentrations were in the range of four orders of magnitude (4-14000, average 570 ľg L-1 Xanthan equivalent), with greatest variations in the upper water column (0, 5 and 10 m of depth). The lowest TEP concentrations were determined in 1999, the year without mucilage events. Among the years with mucilage events (2000, 2001 and 2002) exceptionally high values occurred in 2002, when the event was more pronounced. Increased TEP concentrations in the seawater preceded the mucilage formation and decreased during the events, when significant portion of TEP was most likely included in aggregates. In all years TEP formation was the most intensive in the upper water column in March/April periods when phytoplankton biomass, as a major TEP source, increased. During the summers TEP concentrations were higher then average, probably due to longer "residence time" in relation to chlorophyll a in conditions or reduced water exchange rates with the rest of the Adriatic. Significant positive correlations between TEP and chlorophyll a, pheophytin and bacterial abundance and negative between TEP and salinity were found in February-August periods, while less significant in September-January periods, when TEP concentrations were lower. In conclusion, TEP in the northern Adriatic is being formed in high quantities in periods preceding the mucilage formation with phytoplankton as a major source and probably important, but still not fully explained role of bacteria.

TEP; Northern Adriatic; Mucilage events

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