Ecosystem structure in disturbed and restored subtropical seagrass meadows

Abstract

Physical disturbance to seagrass ecosystems removes plant biomass, but impacts to habitat quality and nutrient storage and cycling are not well understood. Seagrass restoration actions provide a management tool intended to accelerate the recovery of lost ecosystem structure and function following disturbance. We studied the plant community and sediment structure at vessel grounding disturbances in seagrass ecosystems to better understand the nature of such impacts, and how structure changed with time. We conducted a similar analysis of seagrass restoration sites of different ages, to determine if restoration accelerates the recovery of lost ecosystem structure in the plants and sediments. Disturbance to seagrass sediments resulted in loss of seagrass community structure and diminished sediment and porewater nutrient pools. These impacts persisted in our study sites that were up to five years in age since impact. Another effect of physical disturbance is the loss of nutrients stored in the sediments. Restoration sites that received fill were characterized after 3 to 3.5 years by low macrophyte cover and by sediments with greater bulk density and redox potential, and low sediment and porewater nutrient pools. We did not detect substantial convergence of seagrass and sediment structure with the intact seagrass ecosystem in either the disturbed or the restoration sites we studied. However, our study sites were still in a recent period of recovery following disturbance or restoration. Longer time frames will be needed to identify ecosystem recovery trajectories following disturbance and restoration in this system.