Application of spectrofluorimetric techniques to the study of marine mucilages in the Adriatic Sea: preliminary results

The use of spectrofluorimetric techniques was investigated both to analyse the mucilage material of the Adriatic Sea, and to explore the transformation of extracellular exudates produced by ageing cultures of diatoms. A series of mucilage samples, collected in 1989, 1991 and 1992, was analysed by fluorimetry. The synchronous spectral responses of the field samples were compared with the extracellular exudate spectra of Skeletonema costatum and Nitzschia closterium, isolated from Adriatic aggregates and cultured in the laboratory. The analysis showed an evident similarity of the spectra, characterized by a main peak, located at the excitation wavelength of about 280 nm and by a series of secondary peaks, ranging from 340 to 500 nm. Filtered samples, taken from a number of differently aged cultures, showed in all cultures analysed a decreasing trend in time of the first peak, with parallel increase of the peaks at higher wavelengths, indicating a qualitative transformation of the dissolved organic matter. The trend was described by the intensity ratio between the peaks located at 280 and > 300 nm, respectively. The intensity ratio, calculated on the last series of peaks showed, instead, some differences among species. This ratio seems to provide a qualitative characterization of the extracellular organic matter produced by different species.