Flowering of Zostera marina in the Lagoon of Venice (North Adriatic, Italy)

The flowering of Zostera marina was studied in a shallow meadow in the Venice lagoon (North Adriatic Sea) in spring and summer 1995. Vegetative and fertile shoot density and size were recorded during the flowering period. Spathe maturation was divided in six phases according to different stages of anthesis. New spathes were first observed in February and anther and pistil maturation proceeded until March. The beginning of anthesis, with styles erecting, occurred in April while fruits appeared in May and June. A statistically significant difference between fertile and vegetative shoot height was found for all months. The start of flowering (February-March) appears to be early in the Venice lagoon in comparison to Atlantic European sites, where it starts from June onward. A six-month long flowering period is one of the longest observed. The estimated potential seed production seems limited if compared with the values relative to North European and North American coasts.