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Time series of soluble extracellular polymeric substance (S-EPS) and transparent exopolymer particle (TEP) fractions, as well as biological, physical and chemical parameters, were studied in natural phytoplankton assemblages at 2 macrotidal sites located in the English Channel for 3 yr. The first site, the Bay des Veys (BDV), is sheltered from prevailing winds and influenced by a high river discharge, whereas the second, Lingreville-sur Mer (LGV), is exposed to the open ocean and to dominant winds. At both sites, the highest TEP concentrations were measured in spring and summer (1735 and 3604 µg equiv X l -1 at BDV and LGV, respectively) and were correlated with phytoplankton biomass and nitrogen concentrations. During the autumn and winter, TEP dynamics were not related to phytoplankton dynamics but appeared controlled by hydrodynamics. In contrast to TEP concentrations, S-EPS did not present any seasonal dynamics and was not correlated with TEP variations. The highest amount of S-EPS was recorded in spring at LGV (25.8 mg equiv. glucose l ). The S-EPS pool was separated in 2 fractions according to the molecular weight: low (LW) and high (HW). The LW fraction was produced in higher quantity than the HW fraction, and with larger temporal fluctuations. Therefore, both S-EPS fractions seem controlled by different environmental parameters depending on the season and on the studied ecosystem. The different dynamics observed for TEP and S-EPS confirm the complexity of carbon excretion processes in phytoplankton, and the results reveal different metabolic pathways and different origins for these carbon excretions. KEY WORDS: Transparent exopolymer particles · TEP · Soluble EPS · Diatoms · Eastern English Channel · Environmental parametersResale or republication not permitted without written consent of the publisher

The effect of ra~n-borne nutnents in spring on the marine microbial community was studied In Villefranche Bay (France), a system in which prevlous studies have suggested that competition exlsts within the microbial food web for nutrient salts In 5 incubalon expenrnents conducted from May 1994 to March 1996, surface seawater was amended with 2 to 8 % (v/v) rainwater additions The additions yielded final nutrient concentrations from 0 98 to 5 93 pM of dissolved inorganic nitrogen (NH,+ + NO,-forms) and 0 to 0 05 PM of inorganic phosphorus (PO,'-) In 4 out of 5 experunents signlficant increases in chlorophyll a (chl a ) were detected The ratio of added N (py 1 -l ) to apparent increase in chl a (pg 1.' ) averaged about 100 The increases in chl a were correlated with Increases in abundances of phototrophic nanoflagellates (PNAN] In contrast to chl a and PNAN stocks, no effect of rainwater addition was evident among the populatlons of autotrophic bacteria (Synechococcus sp ), heterotrophlc bactena or the predators of bacteria heterotrophic nanoflagellates In one expenment, there was no significant effect of rainwater addition however, nutnent concentrations of unamended seawater samples were high (1 0 PM DIN 0 06 pm P o d 3 ) Our data indicate that in late spnng, when the NW Mediterranean is most likely nitrogen limited rain-borne 'new nutnents appear to benefit small eucaryotic phytoplankton, PNAN, rather than autotrophic or heterotrophic bactenal populations or larger phytoplankton K E Y WORDS: Nitrogen . Rain . Bactenoplankton . Phytoplankton . Synechococcus

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