Large-scale eelgrass transplantation: a measure for carbon and nutrient sequestration in estuaries

Abstract

The accelerated global losses of seagrass meadows makes restoration increasingly important. This restoration study was conducted in a shallow Danish estuary and describes one of the rare examples of successful large-scale eelgrass Zostera marina restoration outside North America. A simplified 3-step site selection approach was successfully applied to locate an optimal site for large-scale transplantation. It consisted of (1) qualitative assessments of vegetation using aerial photos, (2) inspection of potential sites with assessments of stressor presence and potential growth conditions and (3) transplantation tests for a final assessment of site suitability and methodology. The large-scale transplantation was initiated at the test site with the highest shoot production. After transplantation, shoot densities developed rapidly, achieving a 70-fold increase in density after about 2 yr. A rapid edge expansion (0.32 m yr-1) of the transplanted area was detected using drone-based monitoring. Both the final shoot density and edge expansion were comparable to those of natural eelgrass patches in the estuary. Eelgrass-transplanted areas accumulated more fine sediment particles and organic C, N and P than adjacent unvegetated sediment. Burial of organic C, N and P in eelgrass-transplanted sediments was 33 ± 7.5, 6.6 ± 0.9 and 3.0 ± 0.5 g m-2 yr-1, respectively (mean ± SE). In addition, inorganic C and N were assimilated by eelgrass transplants at rates of 290 ± 22 and 12 ± 1.0 g m-2 yr-1, respectively. The results highlight that important ecosystem services are already restored 2 yr after successful eelgrass restoration.

Nordic Blue Carbon Ecosystems: Status and Outlook

“…Persistent Nordic restoration efforts confirm these recommendations and provide best practices for site selection and full-scale restoration (e.g. Moksnes et al, 2016;Lange et al, 2022). The most successful Nordic eelgrass restorations have involved eelgrass transplants rather than seeds, and have sometimes involved anchoring of shoots, stabilization of sediments by protective structures, sandcapping, enclosures to avoid bioturbation, traps to reduce crabs, or co-restoration with blue mussels in order to facilitate eelgrass survival and growth (Moksnes et al, 2016;Gagnon et al, 2021;van der Heide et al, 2021Lange et al, 2022) (Table S7).…”

“…Moksnes et al, 2016;Lange et al, 2022). The most successful Nordic eelgrass restorations have involved eelgrass transplants rather than seeds, and have sometimes involved anchoring of shoots, stabilization of sediments by protective structures, sandcapping, enclosures to avoid bioturbation, traps to reduce crabs, or co-restoration with blue mussels in order to facilitate eelgrass survival and growth (Moksnes et al, 2016;Gagnon et al, 2021;van der Heide et al, 2021Lange et al, 2022) (Table S7). Target areas for restoration have been identified by modelling where eelgrass habitat requirements are fulfilled (e.g.…”

“…Target areas for restoration have been identified by modelling where eelgrass habitat requirements are fulfilled (e.g. Canal-Vergeś et al, 2016;Flindt et al, 2016) supplemented with further site inspection and transplantation trials (Lange et al, 2022). However, because eelgrass restoration is labor intensive, costly and with no guarantee of success, protection of existing meadows is a management priority (Moksnes et al, 2016).…”

Unoccupied aerial vehicle-assisted monitoring of benthic vegetation in the coastal zone enhances the quality of ecological data

“…Having the ability to precisely estimate the standing stock of eelgrass and macroalgae biomass and thus nutrient content is important both in defining the value of ecosystem services and monitoring seagrass restoration success (Lange et al, in prep; Orth et al, 2020); to calculate the effectiveness of these habitats to sequester blue carbon (Howard et al, 2017; Mazarrasa et al, 2018; Sousa et al, 2019), and for validating ecological models (Kuusemäe et al, 2016). Macroalgae also have a somewhat undisclosed role as carbon sinks and as such precise biomass mapping may support future studies aiming to quantify this role (Krause-Jensen and Duarte, 2016).…”

A Revision of the Traditional Analysis Method of Allometry to Allow Extension of the Normality-Borne Complexity of Error Structure: Examining the Adequacy of a Normal-Mixture Distribution-Driven Error Term

“…But despite the ecological relevance of eelgrass meadows, deleterious anthropogenic influences currently threaten their permanence [ 24 ]. Eelgrass remediation efforts mainly rely on transplanting endeavors [ 25 ]. Assessing the success of concurring plots depends on nondestructive estimations of standing stock from which total leaf biomass is an important constituent.…”