A quantitative synthesis of approaches, biases, successes, and failures in marine forest restoration, with considerations for future work

Abstract

1. Marine forests is a term commonly used for coastal marine habitats formed by dense stands of brown macroalgae, typically consisting of kelp and fucoids. These habitats are highly productive, offer habitat to numerous marine organisms, and support a range of invaluable ecosystem services. Despite their importance, marine forests are declining in many regions around the world as a result of interacting global, regional, and local-scale stressors. Consequently, interest in restoration as a tool to mitigate these declines and reinstate marine forests is growing.2. Recent reviews have provided insights into marine forest restoration; however, for the most part, a synthesis of restoration success is lacking. A meta-analysis and quantitative review of published marine forest restoration efforts was conducted to examine: (i) how restoration affects the abundance and morphology of marine forest species; and (ii) trends in marine forest restoration success.3. The meta-analysis of 25 studies revealed that restoration positively influences the abundance and morphology of marine forest species. The quantitative review of 63 studies demonstrated that taxa and restoration technique were important factors influencing restoration success, and revealed a bias towards the monitoring and reporting of abundance and morphological response variables.The review also highlighted a lack of monitoring and/or reporting of environmental variables at restoration sites, and limited comparative research across environmental contexts and restored species. 4. It is shown that successful marine forest restoration is possible at experimental scales, but that better monitoring and reporting of restoration efforts, alongside increased project durations, could improve our understanding of restoration success at the ecosystem level. Considerations for future marine forest restoration efforts are also provided. It is hoped that the review will advance marine forest restoration efforts, allowing the preservation of these valuable ecosystems and their associated services.

An assessment of the utility of green gravel as a kelp restoration tool in wave-exposed intertidal habitats

“…In summary, while there is little evidence of kelp forest declines and/or losses around the UK, there is a need to test and refine restoration techniques in a variety of contexts and including a range of species so that in the future swift action can be taken to mitigate declines and conserve kelp forests. Green gravel is one technique within a suite of restoration tools (Earp et al ., 2022) that could be used to combat future declines and/or losses of both kelp and other forest-forming macroalgae, and it could be used to propagate resilient genotypes and ‘future-proof’ vulnerable kelp forests to future stressors (Wood et al ., 2019; Coleman et al ., 2020). While our initial testing of this technique on wave-exposed intertidal shores was unsuccessful, it provides important insights for developing/refining the technique further for a wider range of environmental conditions, as well as a baseline for comparison for future efforts.…”

“…Consequently, interest in restoration as a tool to initiate or accelerate the recovery of habitats that have been degraded or lost is growing. In the marine realm, restoration has somewhat lagged behind terrestrial systems, although advances have been made in multiple habitat types including mangrove forests (Kamali and Hashim, 2011), seagrass meadows (Bull et al ., 2004; Marion and Orth, 2010; van Katwijk et al ., 2016; Unsworth et al ., 2019), coral reefs (Rinkevich, 2005; Young et al ., 2012; Boström-Einarsson et al ., 2020), oyster reefs (Brumbaugh and Coen, 2009; Richardson et al ., 2022), and more recently kelp forests (Westermeier et al ., 2016; Fredriksen et al ., 2020; Graham et al ., 2021; Earp et al ., 2022; Miller and Shears, 2022; Eger et al ., 2022a).…”

“…As such, active restoration techniques including transplanting and seeding are necessary to restore kelp forests in some regions (Vásquez and Tala, 1995; Hernandez-Carmona et al ., 2000; Campbell et al ., 2014; Westermeier et al ., 2014; Layton et al ., 2021). Active restoration can however be costly, challenging to implement at relevant spatial scales, and has often only been trialled on one species and/or in one environmental context (Earp et al ., 2022). In particular, the majority of Laminarian kelp restoration efforts have been undertaken in subtidal areas (Earp et al ., 2022), with limited information regarding the suitability of trialled restoration techniques in intertidal environments.…”

“…Active restoration can however be costly, challenging to implement at relevant spatial scales, and has often only been trialled on one species and/or in one environmental context (Earp et al ., 2022). In particular, the majority of Laminarian kelp restoration efforts have been undertaken in subtidal areas (Earp et al ., 2022), with limited information regarding the suitability of trialled restoration techniques in intertidal environments.…”