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

Flowering intensity and allocation patterns in relation to shoot dynamics w ere evaluated in six perennial eelgrass stands from Limfjorden, Denmark. Fl owering shoot density peaked in May at 79 +/- 20 m(-2) (mean +/- SE, n=6), and the cumulative production over the flowering season (March-August) aver aged 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 con stitutes 5.8 +/- 1.0% of annual above-ground production. Eelgrass shoots we re 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 una ble to account for different flowering frequency among the six stands. Flow ering individuals had many seeds, and seed production was high (8100 +/- 16 00 m(-2)) compared with other perennial eelgrass populations. Shoot recruit ment achieved through branching averaged 796 +/- 122 m(-2) per year and onl y 15% of these reached the age of potential seed production. Ln early sprin g, seedling density was-high within the vegetation (282 +/- 61 m(-2)). Beca use the majority of seedlings were shaded out during summer, vegetative pro pagation was, however, more important for growth and maintenance of the stu died eelgrass stands. (C) 1999 Elsevier Science B.V. All rights reserved.