Abstract

Spatial and size distribution of micro-organisms and their ETS activity has been investigated in Ligurian Sea surface waters along the Nice-Calvi transect across frontal areas from 18 to 37 km offshore (TOMOFRONT 1 and 2 cruises, April 1988 and April-May 1989 respectively). Aplastidic and plastidic nanoflagellates and aplastidic picoflagellates were present in numbers close to 0.25 × 104 cells ml−1, whereas plastidic picoflagellates accounted for about half this number. Correlations have been evidenced between plastidic and aplastidic micro-organisms within the same size group, suggesting that they belong to a well-defined ecosystem. The highest correlation between total ETS activity and abundance of the considered size groups was observed for nanoflagellates (r = 0.94, n = 22, and r = 0.90, n = 22 for aplastidic and plastidic cells respectively). The importance of the role of nanoflagellates in surface waters, with respect to the overall ETS activity, was supported by results from size fractionation which assigned to the 3–10 μm size range a 73.3% contribution to overall ETS activity. Results emphasize analysing global ETS activity of natural samples in order to derive relationships between the different populations present in the sampled water. It is suggested that coupling flow cytometry to the ETS approach should be very helpful in that respect.

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