Restoration of seagrass habitat leads to rapid recovery of coastal ecosystem services

Abstract

There have been increasing attempts to reverse habitat degradation through active restoration, but few large-scale successes are reported to guide these efforts. Here, we report outcomes from a unique and very successful seagrass restoration project: Since 1999, over 70 million seeds of a marine angiosperm, eelgrass (Zostera marina), have been broadcast into mid-western Atlantic coastal lagoons, leading to recovery of 3612 ha of seagrass. Well-developed meadows now foster productive and diverse animal communities, sequester substantial stocks of carbon and nitrogen, and have prompted a parallel restoration for bay scallops (Argopecten irradians) Restored ecosystem services are approaching historic levels, but we also note that managers value services differently today than they did nine decades ago, emphasizing regulating in addition to provisioning services. Thus, this study serves as a blueprint for restoring and maintaining healthy ecosystems to safeguard multiple benefits, including co-benefits that may emerge as management priorities over time.

Fig. 1. Eelgrass cover and seedling data for the coastal bays.

(A) Cover (in hectares) of eelgrass in each of the four coastal lagoons (South Bay, Hog Island Bay, Spider Crab Bay, and Cobb Bay: see inset) and all four bays combined (inset shows the geographic layout of these locations). (B) Cumulative seeded area for each bay. (C) Seedling establishment rates for seeds broadcast into the coastal bays in the preceding years; rates were not measured in each bay in each year, so data reflect the aggregate across all sites measured within a year.

Fig. 2. Seagrass cover in the four bays for four time periods: 2001, 2006, 2010, and 2018.

Cover estimates (very sparse, 1 to 10%; sparse, 11 to 40%; moderate, 41 to 70%; dense, 70 to 100%) indicated by color in each polygon. Small squares in each box represent restoration plots (light green are plots done that year; dark green are plots done in previous years).

Fig. 3. Aerial image of South, Cobb, and Spider Crab bays showing seagrass cover (dark areas) in 2018 and location of seed restoration plots (yellow boxes).

Fig. 4. Mean turbidity [Nephelometric Turbidity unit (NTU)] ± 1 SE from continuous environmental monitoring from a YSI in the main bed of South Bay during summer months (May to August, reflecting peak annual seagrass biomass) against total area of seagrass obtained from the aerial survey immediate to the environmental sonde (northern part of South Bay).

Fig. 5. Ecosystem services associated with the restoration of eelgrass over time. Mean (solid lines) and 95% confidence intervals (dotted lines) over time (mT = metric tons).

(A) Net sediment carbon stocks. (B) Net sediment nitrogen stocks (net stock = seagrass sediment stock − unvegetated sediment stock). For sediment nutrient stocks, measurements were taken in beds of varying ages and these values were matched with the corresponding year since the beginning of the restoration. (C) Total invertebrates. (D) Total fish biomass. For faunal communities, data were collected in various years, and averages/standard deviations were used to interpolate values for years in which no data were available. Both measurements were expressed per unit area and extrapolated to the total bed area for each year.

Fig. 6. Estimates of total bay scallop abundances in South and Cobb bays based on annual surveys begun in 2013.