Primary Research Paper Seasonal dynamics of Zostera noltii Hornem. in two Mediterranean lagoons Christine Pergent-Martini 1 , Vanina Pasqualini 1, *, Lila Ferrat 1 , Ge´rard Pergent 1 & Catherine Fernandez 2 1 University of Corsica, Faculty of Sciences, Equipe Ecosyste`mes Littoraux, BP 52, 20250 Corte, France 2 University of Provence, IMEP UMR-CNRS 6116 - Centre St Je´ro ˆme- case 421bis, 13387 Marseille cedex 20, France (*Author for correspondence: Tel.: +33-4-9545-0055, Fax: +33-4-9546-2441, E-mail: pasquali@univ-corse.fr) Received 26 July 2004; in revised form 30 November 2004; accepted 9 December 2004 Key words: coastal lagoon, Mediterranean, population dynamics, seagrass, Zostera noltii Abstract The density, biomass and shoot morphology of two populations of Zostera noltii were monitored from January 1998 to July 1999 at two shallow Mediterranean lagoons of Biguglia and Urbino, which differ in hydro-morphological conditions and nutrient loading. Monitoring included the principal biological and foliar parameters (shoot density, aboveground and belowground biomass, length, width and number of leaves, LAI and coefficient A: percentage of leaves having lost their apex), the organic matter contents of the sediment and the environmental conditions (salinity, turbidity, temperature, nutrient concentrations and dissolved oxygen levels). The two populations of Z. noltii displayed seasonal changes in density (1600– 19600 m 2 ), aboveground biomass (11–153 g. DW. m )2 ), leaf length (33–255 mm), and leaf width (0.9– 1.8 mm). Temperature and turbidity were significant environmental factors influencing the temporal changes observed in the Z. noltii meadows studied. Conversely, the belowground biomass, the number of leaves per shoot and the LAI did not undergo any seasonal changes. In the Biguglia lagoon, the functioning dynamics of the Z. noltii seagrass beds are determined by the catchment area and the inputs of nutrients derived from it, whereas in the Urbino lagoon the dynamics of the Z. noltii beds depend on low levels of water turbidity. Introduction Sixty seagrass have been described in the world (Kuo & Den Hartog, 2001), but the only genii found in the Mediterranean biogeographical area are Cymodocea, Halodule, Halophila, Posidonia, Ruppia and Zostera. The genus Zostera is a major component of Mediterranean lagoon ecosystems (Sfriso & Ghetti, 1998; Agostini et al., 2003). There are only two species of Zostera: Zostera marina L. and Zostera noltii Horneman. The distribution of seagrasses is influenced by various environmental parameters (Hemminga & Duarte, 2000), such as hydrodynamic conditions, nature of the substrate, light (Peralta et al., 2002), temperature (Pe´rez-Llore´ns & Niell, 1993; Marba et al., 1996), salinity (Wortmann et al., 1997), nutrient concentrations in the water column (Orth, 1977) and/or in the sediment (Viaroli et al., 1997). Increasing anthropogenic pressure on Medi- terranean lagoons (industry, agriculture, aquacul- ture and domestic waste), has led to the decline or even disappearance of seagrasses (Van Lent et al., 1995; Frederiksen et al., 2004) and to the prolif- eration of Chlorophyta, which is more favoured by increase in nutrients and pollutants (De Casabianca et al., 2002). Studies have therefore been carried out to assess the impact of human activities on the seasonal dynamics of seagrasses Hydrobiologia (2005) 543: 233–243 Ó Springer 2005 DOI 10.1007/s10750-004-7454-7