Distribution, biomass and phenology of Zostera noltei meadows in the Northern lagoon of Tunis in the summer of 2014

Seagrass meadows of Zostera noltei are widely distributed over the coasts of Tunisia and represent relatively dominant populations in the Northern lagoon of Tunis. This brackish environment was the subject of a plan of restoration and development implemented in the mid 1980’s to deal with problems of eutrophication. This work is a contribution to the characterization of seagrass meadows of Z. noltei in the Northern lagoon of Tunis, with (i) mapping meadows along 36 equally spaced and well distributed transects, (ii) measuring the biomass with its two components, above and below-ground, in representative stations of different types of seagrass meadows, and (iii) the observation of phenological characteristics of the plant. The results show that Z. noltei meadows grow over 40% of the total area of the lagoon. They spread gradually to the Southern part of the lagoon where they are able to survive and to thrive. The total biomass in the North lagoon of Tunis was about 2512 tons of DW in June of 2014. Most of this biomass comes from dense beds with cover of 50 to 90%. The phenological characteristic analysis shows that the mean density is about 1830 shoots/m², the average length and average width of the leaves are 26.6 cm (SD = 6.9) and 1.8 mm (SD = 0.2), respectively. Depending on the type of cover, the total length of rhizomes varies between 2.3 and 40.6 m/m² and the average number of leaves/shoot is between 3.1 and 4.5 (SD = 0.4). Flowering, which begins in April, continues until the end of August. The flowering rate varies between stations, ranging from 0 to 16% in June of 2014. The study should be extended to other seasons to better understand the characteristics and dynamics of Z. noltei meadows, which have a very important role in the restoration and the ecological balance of the Northern lagoon of Tunis.