SEASONAL SURVEY OF METAZOAN MEIOFAUNA AND SURFACE SEDIMENT ORGANICS IN A NON-TIDAL TURBULENT SUBLITTORAL PRODELTA (NORTHWESTERN MEDITERRANEAN)

As part of the French research program ECOMARGE, metazoan meiofauna ab undances along with local physical, chemical and microbial characteris tics were monitored generally monthly over a 14-month period in a silt y-muddy prodelta located at 26 m depth off the Tet River outlet in the northwestern (NW) Mediterranean. Meiofauna densities ranged from 1266 to 5586 individuals 10 cm-2, and were dominated by nematodes (91-98%) , followed by harpacticoid copepods (1.37-6.96%) and kinorhynchs (up t o 1.40%). Bottom water temperature varied between 9.5-degrees-C in win ter to over 20-degrees-C in early autumn. All parameters analysed in t he surface sediment also exhibited high temporal variability: fine par ticle content (7.6-18.4% < 40 mum), calcium carbonate (5-8.6%), total organic carbon (4.1-7.3 mg g-1), organic nitrogen (0.35-0.95 mg g-1), C:N ratios (5.6-19.7), total amino acids (159-2358 mug g-1) and sugars (315-1553 mug g-1), lignin by-products (6-61 mug g-1), chlorophyll-a (0.30-1.20 mug g-1), phaeopigments (1.12-3.62 mug g-1), total chloropl astic pigments (1.42-4.58 mug g-1), viable bacterial numbers (1.9 x 10 (5)-3.9 x 10(7) Colony Forming Units ml-1), microheterotrophic total u ptake (18.3-74.2% after 5 h) and respiration (5.2-28.8%) of C-14-gluco se. Seasonal trends were not always obvious, and some variables were s ignificantly correlated with each other. Because the survey was carrie d out in a complex system affected by strong frequent winds and irregu lar discharges of the river, different expressions of these climatic f actors were included in the data set in an attempt to understand the r elationships between variables and ultimately highlight the forces dri ving the observed abundance patterns. Further analysis showed that: (1 ) most of the parameters were strongly influenced by the climatic even ts that occurred prior to sampling, and (2) most of the correlations w ere largely explained by the concomittant influence of these events on the corresponding variables. Although some parameters were enhanced, many were affected negatively due to physical disturbance (mixing, res uspension, erosion). The observed patterns and relationships appeared to result primarily from the high physical variabilily of the system c ombined with low sampling frequency.