Seed Dispersal in a Marine Macrophyte: Implications for Colonization and Restoration

Abstract

Seagrasses rely on both vegetative (rhizome elongation) and sexual propagation for maintenance of existing beds and colonization of new areas.Ye nisms of seed dispersal and survival of seeds in new areas remain poorly descri conducted seed dispersal experiments in the field and laboratory to better desc dispersal characteristics in one species, Zostera marina L. (eelgrass), the dominant species in the temperate zone of the United States, Japan, and Europe.Seeds were broadcast by hand into unvegetated 5 m diameter plots at three l over 3 yr (1989)(1990)(1991) in the York River, Virginia (Chesapeake Bay).These sites previously vegetated but were devoid of any vegetation prior to (since 1972) an the course of the experiments.Resultant seedling distributions closely matched b patterns, with 80% of all seedlings found within the 5 m diameter plots, despite that geophysical processes would appear sufficient to transport seeds greater d Wind records for the 2-mo period between seed broadcasting and germination time-averaged wind speeds in excess of 40 km/h on 12 d in each of the 3 yr an force winds (72 km/h) in 2 of 3 yr.A three-dimensional hydrographic computer s model of the York River provided instantaneous current velocity estimates fro maximum bottom shear velocities (u.) in the study area were approximated (flo 1.26 cm/s, ebb tide: 1.20 cm/s).These estimates exceeded the critical erosion th (ucrit = 0.7 cm/s) for Z. marina seeds determined from laboratory flume experim postulate that small-scale topographic features on the bottom (burrows, pits, m ripples) shield the seeds from the flow.Our results suggest that seeds settle rapidly, dispersing only up to a few metre the influence of currents and become rapidly incorporated into the sediment.Th dispersal capabilities of seeds underscore the need to address restoration goals and of seagrass ecology in the context of landscape-scale distributional patterns and me tion analyses.