Reproduction in Danish eelgrass ( Zostera marina L.) stands: size-dependence and biomass partitioning

Abstract

Flowering intensity and allocation patterns in relation to shoot dynamics were evaluated in six perennial eelgrass stands from Limfjorden, Denmark. Flowering shoot density peaked in May at 79 ± 20 m −2 (mean ± SE, n = 6), and the cumulative production over the flowering season (March–August) averaged 111 ± 22 m −2. This investment represents 48 ± 9 g DW m −2 y −1, is 2.5 times higher than the maximum biomass of flowering shoots, and constitutes 5.8 ± 1.0% of annual above-ground production. Eelgrass shoots were one year or older, and weighed more than 35 mg DW before they flowered. Despite the size and age dependence of flowering, these attributes were unable to account for different flowering frequency among the six stands. Flowering individuals had many seeds, and seed production was high (8100 ± 1600 m −2) compared with other perennial eelgrass populations. Shoot recruitment achieved through branching averaged 796 ± 122 m −2 per year and only 15% of these reached the age of potential seed production. In early spring, seedling density was high within the vegetation (282 ± 61 m −2). Because the majority of seedlings were shaded out during summer, vegetative propagation was, however, more important for growth and maintenance of the studied eelgrass stands.