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Restoration is accelerating to reverse global declines of key habitats and recover lost ecosystem functions, particularly in coastal ecosystems. However, there is high uncertainty about the long‐term capacity of restored ecosystems to provide habitat and increase biodiversity and the degree to which these ecosystem services are mediated by spatial and temporal environmental variability. We addressed these gaps by sampling fishes biannually for 5–7 years (2012–2018) at 16 sites inside and outside a rapidly expanding restored seagrass meadow in coastal Virginia (USA). Despite substantial among‐year variation in abundance and species composition, seine catches in restored seagrass beds were consistently larger (6.4 times more fish, p < 0.001) and more speciose (2.6 times greater species richness, p < 0.001; 3.1 times greater Hill–Shannon diversity, p = 0.03) than seine catches in adjacent unvegetated areas. Catches were particularly larger during summer than autumn (p < 0.01). Structural equation modeling revealed that depth and water residence time interacted to control seagrass presence, leading to higher fish abundance and richness in shallow, well‐flushed areas that supported seagrass. Together, our results indicate that seagrass restoration yields large and consistent benefits for many coastal fishes, but that restoration and its benefits are sensitive to the dynamic seascapes in which restoration is conducted. Consideration of how seascape‐scale environmental variability affects the success of habitat restoration and subsequent ecosystem function will improve restoration outcomes and the provisioning of ecosystem services. [ABSTRACT FROM AUTHOR]

Seagrass restoration can help reverse global meadow loss and restore ecosystem services, including habitat provision for commercial fish and shellfish, carbon sequestration, and improved water quality. However, restoration projects are generally expensive, and site selection remains a challenge due to uncertainty about how environmental variables affect the survival and spread of seedlings. Long-term Zostera marina (eelgrass) success/failure and expansion data from the Virginia Coast Reserve can be used to determine whether the factors that control seedling survival also explain the regional distribution of seagrass meadows. We tracked plant survival and failure within restoration plots and at natural recruitment sites from 2001 to 2015 and used machine learning methods to identify the relative importance of multiple environmental predictors, including water residence time, fetch distance, water temperature, depth, and sediment grain size. Low water residence time was the best predictor of survival, but short fetch length best explained the natural recruit distribution, consistent with hydrodynamic control of seed dispersal. Restoration plot data suggests that the eelgrass fundamental niche covers > 100 km2 within this system, triple both the current extent and the realized niche predicted by the observed natural spread. Our results corroborate historical records that eelgrass was formerly widespread in areas where it has not spread naturally, likely due to insufficient seed delivery. Additional seeding in these areas would, therefore, increase total seagrass coverage and accelerate recovery. Mapping the total habitable area can help managers maximize the extent of seagrass and other bottom uses, including shellfish aquaculture. [ABSTRACT FROM AUTHOR]

Awarding CO2 offset credits may incentivize seagrass restoration projects and help reverse greenhouse gas (GHG) emissions from global seagrass loss. However, no study has quantified net GHG removal from the atmosphere from a seagrass restoration project, which would require coupled Corg stock and GHG flux enhancement measurements, or determined whether the creditable offset benefit can finance the restoration. We measured all of the necessary GHG accounting parameters in the 7-km2Zostera marina (eelgrass) meadow in Virginia, U.S.A., part of the largest, most cost-effective meadow restoration to date, to provide the first seagrass offset finance test-of-concept. Restoring seagrass removed 9,600 tCO2 from the atmosphere over 15 years but also enhanced both CH4 and N2O production, releasing 950 tCO2e. Despite tripling the N2O flux to 0.06 g m−2 yr−1 and increasing CH4 8-fold to 0.8 g m−2 yr−1, the meadow now offsets 0.42 tCO2e ha−1 yr−1, which is roughly equivalent to the seagrass sequestration rate for GHG inventory accounting but lower than the rates for temperate and tropical forests. The financial benefit for this highly successful project, $87 K at $10 MtCO2e−1, defrays ~10% of the restoration cost. Managers should also consider seagrass co-benefits, which provide additional incentives for seagrass restoration. [ABSTRACT FROM AUTHOR]

Accelerating losses of seagrass meadows motivate the restoration of these highly productive and beneficial ecosystems. Understanding how environmental parameters including depth and temperature affect restoration trajectories through time is key to conserving and restoring seagrass meadows. We used a long-term (12-year), landscape-scale experiment to test the effect of depth on eelgrass (Zostera marina) restoration success and resilience to a marine heat wave (MHW) disturbance. We found that depth was a critical determinant of seagrass restoration success, with no long-term success at sites deeper than 1.5 m below mean sea level (MSL) or shallower than − 0.8 m MSL. Seeds germinated below − 1.5 m MSL, but shoots did not persist, confirming earlier predictions from a hydrodynamic-vegetation model. Depth was also a significant predictor of seagrass resilience following MHW disturbance. Our results suggest that areas of restored seagrass that are resilient to temperature stress exist across an intermediate depth range, excluding the shallowest and deepest portions of the full habitable depth range for restored seagrass. Over the next decades, sea-level rise will likely affect both the habitable area and the resilient area, available for seagrass restoration. However, seagrass enhancement of sediment accretion may at least partially offset sea-level rise rates. As ocean temperatures warm and MHWs occur more frequently, the resilience of seagrass meadows to temperature stress will be of increasing concern. These results suggest that depth is a critical parameter that will help determine what areas are most resilient and therefore most suitable for conservation and restoration. [ABSTRACT FROM AUTHOR]

Seagrass meadows perform an important ecological function as filters for incoming nutrients from surrounding watersheds, especially nitrogen (N). By enhancing N removal processes, including N burial in sediments and denitrification, seagrass meadows improve water quality. With accelerating losses of seagrass meadows worldwide, seagrass restoration plays a key role in reestablishing these coastal ecosystem functions. However, few measurements exist of N burial rates in temperate seagrass meadows and none have been published for restored meadows. In this study, we measured N burial rates in a large (6.9 km2) restored eelgrass (Zostera marina) meadow and compared N removal through burial to previous measurements of removal via denitrification. We also compared N removal to inputs from external loading and fixation and to N assimilation in seagrass biomass. We found that, in this meadow, burial was the dominant process of N removal; the burial rate of 3.52 g N m−2 yr−1 was comparable to rates in natural meadows within 10 yr after seeding and was more than 20× the rate in adjacent bare sediments (0.17 g N m−2 yr−1). We also found that the high rates of N assimilation (2.62 g N m−2 yr−1) created a substantial though temporary sink for nitrogen during the growing season. Our results highlight how seagrass meadows mediate N cycling through high rates of burial, which to date has been understudied in the literature. The successful return of the N filter function after restoration, shown here for the first time, can motivate continued efforts for seagrass restoration and conservation. [ABSTRACT FROM AUTHOR]

In this study, we developed a push-pull incubation method to measure denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in subsurface sediments of subtidal seagrass meadows. This subtidal push-pull technique, adapted from a push-pull method developed for intertidal salt marshes, used mini-piezometers to directly sample pore water in the root zone of the seagrass during an in situ incubation. The pore water was amended with 15 [ABSTRACT FROM AUTHOR]

Ecosystem restoration is often costly, but can be effective at increasing biodiversity and ecosystem services. We used a case study-reseeding seagrass to a coastal lagoon-to demonstrate the value of enhanced ecosystem services as a result of restoration. We modeled the recovery of areal plant coverage in a system where seagrasses were lost due to disease and disturbance, and estimated the value of the returned functions of nitrogen removal and carbon sequestration. We estimated, as of 2010, that this restoration removes 170 ton of nitrogen per year via denitrificiation and sequesters carbon at a rate of 630 tons carbon per year in the sediment. Further, we estimated that natural recovery would take more than 100 years to reach the areal coverage achieved by restoration using seeds in just 10 years. Restoration enhanced this recovery, and the earlier establishment of plants results in a net gain of at least 4,100 ton of nitrogen removed from the system via denitrification and 15,000 ton of carbon sequestered in the sediment. These services have significant ecological and societal value. [ABSTRACT FROM AUTHOR]

Seagrass meadows are highly productive habitats that provide important ecosystem services in the coastal zone, including carbon and nutrient sequestration. Organic carbon in seagrass sediment, known as “blue carbon,” accumulates from both in situ production and sedimentation of particulate carbon from the water column. Using a large-scale restoration (>1700 ha) in the Virginia coastal bays as a model system, we evaluated the role of seagrass, Zostera marina, restoration in carbon storage in sediments of shallow coastal ecosystems. Sediments of replicate seagrass meadows representing different age treatments (as time since seeding: 0, 4, and 10 years), were analyzed for % carbon, % nitrogen, bulk density, organic matter content, and 210Pb for dating at 1-cm increments to a depth of 10 cm. Sediment nutrient and organic content, and carbon accumulation rates were higher in 10-year seagrass meadows relative to 4-year and bare sediment. These differences were consistent with higher shoot density in the older meadow. Carbon accumulation rates determined for the 10-year restored seagrass meadows were 36.68 g C m-2 yr-1. Within 12 years of seeding, the restored seagrass meadows are expected to accumulate carbon at a rate that is comparable to measured ranges in natural seagrass meadows. This the first study to provide evidence of the potential of seagrass habitat restoration to enhance carbon sequestration in the coastal zone. [ABSTRACT FROM AUTHOR]