Restoring mussel beds in highly dynamic environments by lowering environmental stressors

Abstract

Restoration of coastal ecosystem engineers that trap sediment and dampen waves has proven to be difficult, especially in the wave-exposed and eroding areas where they are needed the most. Environmental stressors, such as hydrodynamic stress and predation, can only be overcome if transplanted organisms are able to establish self-facilitating feedbacks. We investigate if the artificial lowering of multiple environmental stressors can be used to give transplanted juveniles the opportunity to form a self-sustainable system and thereby increase their long-term survival on wave-exposed and eroding shores. We designed a large field experiment using juvenile mussels (Mytilus edulis) as model species on a wave-exposed tidal flat in the Oosterschelde estuary (the Netherlands). We tested if the environmental stress caused by a high predation pressure and wave-driven dislodgement could be reduced by a combination of artificial structures such as fences (to exclude predatory crabs), attachment substrates (such as coir-net or oyster shells), and breakwaters. Despite a low overall mussel survival (29%), we found that under strong hydrodynamic conditions, experimental fences and attachment substrates increased the retention of transplanted mussel seed. However, modification of local hydrodynamic conditions using breakwaters did not improve mussel coverage preservation. Overall, this study highlights the potential of using techniques that lower multiple environmental stressors to create a window of opportunity for establishment in highly dynamic ecosystems.

Considering the use of subadult and juvenile mussels for mussel reef restoration

“…Biodegradable substrates (coir matting and coir rope) were ineffective at preventing cultured juvenile mussel loss, limiting their use as a tool for restoration, a result consistent with intertidal restoration efforts using blue mussels (de Paoli et al 2015;Schotanus et al 2020). Our method aimed to improve mussel survival by including a period of time that allowed mussels to attach to biodegradable substrates or conspecifics prior to transfer onto soft-sediments (a strategy similar to pre-seeding shell material with oyster larvae for oyster reef restoration; Fitzsimons et al 2019), but this made no difference to the outcome of experiments.…”

“…In wild populations, subadult and juvenile mytilid species minimize predator access and dislodgement by forming an inter‐connected network through mutual attachment of byssal threads to stable substrate and/or conspecifics (Bertolini et al 2018). The addition of materials that promote this clumping behavior may help to support subadult and juvenile mussels to become established over soft sediments (Wilcox & Jeffs 2017; Capelle et al 2019; Schotanus et al 2020). Biodegradable materials can serve as a temporary base that anchors translocated subadult and juvenile mussels to the seafloor without the onerous logistics (e.g.…”

“…regulation of water quality (Nelson et al 2004; Paul 2012), energy transfer (Fodrie et al 2017), dissipation of wave energy (Chowdhury et al 2019), provision of food sources (Paul 2012), and provision of habitat to diverse faunal assemblages (McLeod et al 2019), have prompted global efforts to pursue active seafloor restoration to improve ecosystem health and function (e.g. Crassostrea virginica , Chesapeake Bay, North Carolina, U.S.A., Schulte et al 2009; Ostrea angasi & Mytilus galloprovincialis , Port Phillip Bay, Australia, Hancock et al 2019; Mytilus edulis , Wadden Sea, the Netherlands, Schotanus et al 2020). Although methods for restoring lost oyster reefs have received considerable attention, techniques used to restore subtidal mussel reefs have only recently (<10 years) been investigated as an alternative management intervention to address lost or degraded mussel reef habitat (Jeffs & zu Ermagassen 2019).…”

Promoting self‐facilitating feedback processes in coastal ecosystem engineers to increase restoration success: Testing engineering measures

“…However, the manual placement of individuals in these kinds of patterns by hand can be very labour intensive and is therefore not a practical or cost‐efficient method for large‐scale restoration. Fences similar to those applied in current experiment have been used previously in mussel projects to estimate the abundance of mussel clump dispersal (Reusch & Chapman, 1997) or to protect transplanted mussels against predatory crabs (Schotanus, Capelle, et al, 2020). Just as in our experiment, the fences successfully trapped dislodged mussels.…”

Biogeomorphology, quo vadis? On processes, time, and space in biogeomorphology

“…At the small scale, many contributions have focused on the contributions of individual or small groups of plants or animals on geomorphological processes within reefs (e.g. Salvador de Paiva et al ., 2018; Schotanus et al ., 2020), mudflats and marshes (e.g. Temmerman et al ., 2003; Townend et al ., 2011; Nolte et al ., 2013; Schwarz et al ., 2015; Coleman and Kirwan, 2019; Schepers et al ., 2020) and coastal dunes (e.g.…”