INTRASPECIFIC VARIABILITY OF ZOSTERA-MARINA L (EELGRASS) IN THE ESTUARIES AND LAGOONS OF THE SOUTHWESTERN NETHERLANDS .1. POPULATION-DYNAMICS

Within one geographical region the life-history of different Populations of Zostera marina L. (eelgrass) occurring under varying environmental conditions was followed for 2 years. Life-history strategies ranged from annual to perennial. Comprehensive data on biomass, density, generative reproduction, growth rate and production are given, compared with information in the literature, and discussed. Among populations, total annual aboveground production ranged between 160 and 412 g AFDW (ash-free dry weight) per m2 per year, below-ground production varied from 53 to 132 g AFDW per M2 per year. Flowering shoots had significantly higher growth rates compared with non-flowering shoots. Populations allocated a comparable part of total production towards below-ground structures (22-30%), but investment in reproductive tissue varied widely (1-34%). (Semi-) annuals could be distinguished from perennials by a number of characteristics: relatively small below-ground biomass, high above-ground relative growth rate, high generative reproduction effort and seed production, later seasonal timing and a high variability from year to year. The present study gives substantial data to support the theory that Z. marina in principle strives towards a perennial life-history, while life-histories of the species can range between two extremes (annual and perennial) along a continuum.