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Annual versus perennial growth cycle in Ruppia maritima L.: temporal variation in population characteristics in Mediterranean lagoons (Monolimni and Drana Lagoons, Northern Aegean Sea)

Abstract A perennial population of Ruppia maritima in a permanent lagoon in the Evros Delta grew from April to October and reproduced during summer. Numbers of rhizome and stem internodes increased in spring–summer and in late summer–autumn, revealing two successive periods of both horizontal and vertical expansion; leaf density increased continuously until October (78,210 leaves m−2). An annual population in a temporary lagoon grew and reproduced from May to August, and died afterwards leaving seeds as the habitat temporarily dried. Numbers of rhizome internodes sharply increased only in August, while numbers of stem internodes increased in June, indicating that a slow horizontal expansion was followed by a fast and brief vertical expansion; subsequently a second intense horizontal expansion occurred; leaf density peaked in August (58,080 leaves m−2). Several characteristics increased after mid-spring, attaining similar maximum values in annual and perennial populations. However, the perennial population had larger leaves and higher root biomass, but lower reproductive organ biomass. Rhizome, stem and leaf biomass increased sharply in August (113.2 g dw m−2) in the annual population and progressively up to October (167.8 g dw m−2) in the perennial population. Using principal component analysis, growth and reproduction were found to be mainly affected by temperature.