A Roadmap for the Restoration of Mediterranean Macroalgal Forests

Emma Cebrian,Carlo Cerrano,Giuseppe Guarnieri,Cristina Galobart,Simonetta Fraschetti,Jana Verdura,Laura Tamburello,Bernat Hereu,Cristina Linares,Joaquim Garrabou,Alba Medrano

doi:10.3389/fmars.2021.709219

Abstract

Canopy-forming macroalgae play a crucial role in coastal primary production and nutrient cycling, providing food, shelter, nurseries, and habitat for many vertebrate and invertebrate species. However, macroalgal forests are in decline in various places and natural recovery is almost impossible when populations become locally extinct. Hence, active restoration emerges as the most promising strategy to rebuild disappeared forests. In this regard, significant efforts have been made by several EU institutions to research new restoration tools for shallow and mesophotic reef habitats (e.g., MERCES EU project, AFRIMED, and ROCPOP-life) and effective techniques have subsequently been proposed to promote self-sustaining populations. Recent research indicates that macroalgal forest recovery requires a broad spectrum of measures, ranging from mitigating human impacts to restoring the most degraded populations and habitats, and that the viability of large restoration actions is compromised by ongoing human pressures (e.g., pollution, overgrazing, and climate change). We propose a roadmap for Mediterranean macroalgal restoration to assist researchers and stakeholders in decision-making, considering the most effective methods in terms of cost and cost-effectiveness, and taking background environmental conditions and potential threats into account. Last, the challenges currently faced by the restoration of rocky coastal ecosystems under changing climate conditions are also discussed.

Highlights

Macroalgal forests of canopy-forming fucoids are dominant on rocky reefs along all the Mediterranean coasts (Feldmann, 1937; Giaccone and Bruni, 1973; Verlaque, 1987; Ballesteros, 1992; Assis et al, 2020)
As a response to multiple stressors, including eutrophication, overgrazing, increasing coastal sediment loads, and impacts of urbanization, these habitats in both shallow and deep waters are being lost at alarming rates (Gros, 1978; Munda, 1982, 1993; Sala et al, 1998, 2011; Soltan et al, 2001; Thibaut et al, 2005; Vergés et al, 2014), and previously widespread canopy-forming algae have become extinct or have been reduced to remnant, fragmented, and isolated populations (e.g., Thibaut et al, 2005, 2016; Blanfuné et al, 2016; Mariani et al, 2019)
Very little evidence of natural recovery has been reported in macroalgal forests (Scheffer et al, 2001; Perkol-Finkel and Airoldi, 2010; Iveša et al, 2016), even when the area switches back to conditions before Cystoseira forest decline (Pinedo et al, 2013)

Summary

Introduction

Macroalgal forests of canopy-forming fucoids are dominant on rocky reefs along all the Mediterranean coasts (Feldmann, 1937; Giaccone and Bruni, 1973; Verlaque, 1987; Ballesteros, 1992; Assis et al, 2020). Since these could represent critical conditions or processes limiting the target species survival, strategies to mitigate specific stressors during the restoration actions can be implemented, optimizing restoration success.

Results

Conclusion