Identifying spatio‐temporal trends in seagrass meadows to inform future restoration

Abstract

Seagrass restoration requires information on a range of factors including site environmental conditions, appropriate planting techniques, and the identification of sites most likely to support seagrass. To address the question of where to focus restoration efforts, a key first step is to identify trends in the spatio‐temporal distribution of seagrasses to identify areas of persistence, loss, and recent gains. Areas of recent recovery (and adjacent areas), can then be targeted by practitioners for assisted recovery and restoration, whilst areas of persistent loss can be avoided. Here we identified the contemporary distribution, density, and species composition of seagrass ecosystems (using Sentinel 2 imagery and supervised object‐based imagery analysis) and integrated these data with historic extents to identify spatio‐temporal trends in seagrass distribution in Western Port, Victoria, Australia. Contemporary classifications demonstrated acceptable accuracies (Overall Accuracy 0.77–0.85, User Accuracy 0.76–0.97) and predicted a contemporary seagrass extent of 222 km2; with 48 km2 of low‐density recovery predicted to have occurred since 1999. Comparisons with historical seagrass extents indicated some seagrass recovery since large‐scale losses in 1983, although some areas of loss were also present. Recovery included a net gain of approximately 95 km2 in the past 20 years and an eastward range expansion; suggesting environmental conditions have improved and are now conducive for restoration efforts in some areas. Results demonstrate that accurate, low‐cost, remote sensing of seagrass ecosystems is possible and show how understanding spatio‐temporal trends can guide the spatial allocation of resources by prioritizing areas for restoration where recovery is beginning to occur.

Overcoming ecological feedbacks in seagrass restoration

“…We suggest that the evidence points to clear benefits of burying and securing hessian bags into the sediment. Stabilizing seedlings long enough to allow the beginnings of a rhizome network to develop would then kick‐start a positive feedback process to further stabilize sediments and promote meadow recovery (Dalby et al 2023). However, these benefits may not always apply in environments when hydrodynamic influences are reduced (e.g.…”

Understanding the seagrass‐sediment‐light feedback to guide restoration planning: a case study using Zostera muelleri

“…However, significant declines (up to 70%) occurred in the 1970s and early 1980s (Keough et al 2011) as a result of increased sediment loads and associated reductions in light penetration due to changes in catchment activities, including urban development, vegetation clearing, and the draining of large (approximately 400 km 2 ) areas of local swampland for farming (Keough et al 2011). Recent mapping work suggests that seagrasses within Western Port have recovered naturally (approximately 222 km 2 in 2019; Dalby et al 2023), perhaps due to improved land and catchment management practices in the last 30 years and natural flushing of suspended sediments (Wallbrink et al 2003). As such, environmental conditions within areas of Western Port are now considered suitable for assisted recovery.…”

Synthesis of special feature —Tailored Restoration Response: Predictions And Guidelines For Wetland Renewal

“…(P12): In the study investigating the role of light environment in the success of seagrass restoration, Dalby et al (2023) provide evidence that shoot density and leaf size of the seagrass species Zostera muelleri decrease with decreasing light availability. To improve the success of restoring seagrass beds in degraded environments, the local water clarity in relation to the local processes of sediment resuspension and deposition must be accounted for.…”