Indexed on: 21 Jul '16Published on: 15 Jul '16Published in: Aquatic Botany
Submerged aquatic vegetation (SAV) that recruits from seed may be favored over species that maintain populations through clonal reproduction as estuaries become more dynamic with upstream hydrologic changes and sea level rise. We examined recruitment in the SAV species Ruppia maritima (wigeongrass) at the hydrologically variable Everglades-Florida Bay ecotone. We hypothesized that the R. maritima seed bank depends upon large reproductive events occurring at least annually. Vegetation biomass, nutrient allocation, sexual reproduction, seed set and sediment seed bank viability were examined when reproductive meadows were present and following senescence. Within a meadow, total seed bank densities were high (> 20,000 m−2). However, 85% of seeds had germinated, leaving a small persistent seed bank, and most germinations did not successfully produce seedlings. Only 25% of intact (potentially viable) seeds were viable (< 768 seeds m−2) and created a persistent seed bank. As reproductive shoots senesced, all vegetation completely died and 2750 seeds m−2 entered the seed bank (40 seeds g−1 biomass), increasing total viability from < 4 to ∼20%. Reproductive meadows can produce many seeds if not nutrient-limited during “windows of opportunity”; however, no persistent seed bank, high germination rate and total vegetation mortality indicate reliance on recurrent reproductive events for regeneration. Under lower hydrologic variability, perennial populations of R. maritima and other SAV could sustain through vegetative reproduction, reducing dependence on sexual reproduction. Otherwise, SAV in variable environments like this ecotone will remain dependent upon opportunities that allow large reproductive events to sustain seed banks for recruitment and vegetation maintenance.