Green gravel: a novel restoration tool to combat kelp forest decline

Abstract

Kelp forests are in decline globally and large-scale intervention could be required to halt the loss of these valuable ecosystems. To date kelp forest restoration has had limited success and been expensive and unable to address the increasing scale of ecosystem deterioration. Here we developed and tested a new approach: “green gravel”. Small rocks were seeded with kelp and reared in the laboratory until 2–3 cm, before out-planting to the field. The out-planted kelp had high survival and growth over 9 months, even when dropped from the surface. This technique is cheap, simple, and does not require scuba diving or highly trained field workers. It can be up-scaled to treat large areas or even used to introduce genes from more resilient kelp populations onto vulnerable reefs. Green gravel thus overcomes some of the current major limitations of kelp restoration and provides a promising new defense against kelp forest decline.

Restore or Redefine: Future Trajectories for Restoration

“…This could be done through genomic identification of heritable loci under selection for certain stressors combined with manipulative stress experiments using multiple stressors that test the resilience of genotypes possessing such loci and assess potential trade-offs. Genotypes that perform well can then be cultured for enhanced seeding into restored populations (Figure 2; Weeks et al, 2011;Webster et al, 2017;Fredriksen et al, 2020). Given that such approaches, however, could lead to detrimental trade-offs (maladaptation) and decreased resilience to non-target stressors (Hereford, 2009;Anderson et al, 2014), a portfolio approach whereby assisted adaptation is paired with other approaches including enhancing diversity or connectivity, protecting a wide range of seascapes and minimizing stressors (Webster et al, 2017) may provide more security in uncertain futures.…”

Using Propagules to Restore Coastal Marine Ecosystems

“…High fecundity, efficient dispersal and fast growth are all traits that should enable kelps to recolonize extensive areas from a few reproducing parents if suitable conditions exist for survival and growth. There have been multiple efforts to regrow lost or declining kelp forests (reviewed in Layton et al, 2018;Bekkby et al, 2020;Fredriksen et al, 2020), typically through either assisted recovery, in which the focus is on restoring conditions favorable for survival and growth, or active restoration in which kelps are reintroduced to target areas.…”

“…Kelp restoration typically involves transplanting adult or subadult kelp from donor wild or cultured populations, attaching them either directly to the reef or to artificial structures (e.g., Wilson and North, 1983;Hernández-Carmona et al, 2000;Falace et al, 2006;Haraguchi et al, 2009;Campbell et al, 2014). Kelp grow on hard surfaces and are not easily attached, so sometimes this requires labor-intensive drilling or installation of attachment surfaces (reviewed in Fredriksen et al, 2020;Layton et al, 2020). Propagules (spores, gametophytes, zygotes or germlings) have not been widely used.…”

“…This approach fails where established algae such as turfs prevent the settlement of propagules (e.g., Filbee-Dexter and Wernberg, 2018). Consequently, several studies have explored seeding of propagules onto natural or artificial substrates in tanks, which were subsequently out-planted with some success (Falace et al, 2018;Fredriksen et al, 2020 ; Figures 2g,h). Other studies have planted cultured or wild-collected small juveniles, but they tend to succumb to high mortality or yield limited long-term success (Hernández-Carmona et al, 2000;Carney et al, 2005).…”

“…Such technology could encompass multiple stages from collection of propagules to rearing them in tanks or nurseries, and finally dispersing them at the site to be restored. For example, large vessels and booms have successfully been used to collect wild coral-spawn slicks and culture them to viable larvae (Doropoulos et al, 2019b), and tank-based techniques have been used to induce settlement of kelp spores onto gravel which is then scattered onto reefs (Fredriksen et al, 2020). Similarly, with tidal marshes the application of mechanized approaches (for seed collection as well as seeding) and processes that concentrate and efficiently store seed can lead to greater efficiencies in the use of propagules when compared to nursery rearing of seedlings and direct planting.…”