Patterns of shallow seagrass (Posidonia oceanica) growth and flowering along the Tunisian coast

Shoot density and temporal patterns in leaf and rhizome production and other flowering parameters were assessed using a reconstruction technique (Lepidochronology) in Tunisian Posidonia oceanica meadows. Three meadows were sampled in October 2005 while seven in October 2007. Correlation between lepidochronological parameters and climate data (temperature and rainfall) was investigated. Shoot density in the ten meadows varied from 388 +/- 42 shoots m(-2) at El Kantaoui to 893 +/- 109 shoots m(-2) at Rafraf and showing significant differences between all sites. The meadows growing on hard substrate (Rafraf, Nabeul, Hergla cliff, Mandia and Djerba) exhibited the highest shoots densities. Annual leaf formation rate showed a statistically significant difference between localities and years, indicating the importance of interannual growth fluctuations. The meadow in Tabarka produced two more leaves per year (8.3 +/- 0.7) than Rafraf ones (6.3 +/- 0.7). Vertical rhizome elongation rates differed significantly among sites, ranging from higher rates in Tabarka (average 13.72 +/- 2.26 mm year(-1)) to lower rates in El Kantaoui (average 5.01 +/- 1.13 mm year(-1)). The correlation analysis between seagrass growth and climate records showed significant correction between mean rainfall data and vertical rhizome elongation rates. Flowering was most prevalent in 2003. The maximum flowering frequency (FF) and shoot flowering probability (Pf) values were observed in Tabarka. The mean FF and Pf for all studied meadows were respectively estimated to 0.15 +/- 0.09 and 0.011 +/- 0.009. A large spatial-temporal variation in the flowering frequency occurred among populations and between years in P. oceanica meadows along the Tunisian coast. (c) 2011 Elsevier B.V. All rights reserved.