The Role of Habitat and Herbivory on the Restoration of Tidal Freshwater Submerged Aquatic Vegetation Populations

Abstract

Submerged aquatic vegetation (SAV) has declined precipitously throughout coastal areas and its reestablishment has long been an important objective of coastal management. We investigated restoration success of Vallisneria americana (wild celery) using seeds, seed pods, and whole shoot transplants at sites in the Chesapeake Bay in the United States where historical aerial photography has indicated that the species once grew. In addition, we evaluated habitat conditions and established herbivore exclosures to assess the impacts of water quality, sediment conditions, and grazers on planting success. Whole shoot transplants resulted in the most rapid cover of the bottom, but required greater planting effort. Direct dispersal of individual seeds was generally more successful than dispersal of intact seed pods, resulting in more rapid initial seedling growth. Overall, 100% bottom cover of whole shoot transplant plots could be reached in approximately 3 years, despite light attenuation coefficients (Kd) of 3.0 to 4.0. Transplants at shallow depths (<0.5 m) were able to rapidly grow and elongate to the surface at mid-to-low tidal heights. Transplants were successful in both muddy (8% organic) and sandy (<2%) substrates. Using mesh exclosures to protect the plants from herbivory was critical to restoration success. Although water quality and other habitat conditions are important for SAV growth and survival, restoration in the unvegetated areas studied here was limited by grazing of initial recruits. The establishment of protected founder colonies of sufficient size to withstand initial grazing pressures may be required to reestablish SAV in similar areas.