BASE KNOWLEDGE AND IMPLEMENTATIONS IN THE RESTORATION OF MEDITERRANEAN MARINE FORESTS

Brown macroalgae of the genus Cystoseira sensu lato (Fucales, Phaeophyta, henceforth Cystoseira) form dense canopy forests along the coasts of the Mediterranean Sea, sustaining biodiversity and biogeochemical cycles. In the last 4 decades, these habitats have undergone substantial and widespread regression, because of local natural and anthropogenic pressures and, more recently, global climatic stressors. Despite conservation policies have been adopted to passively counteract the deterioration of these habitats, the natural recovery is infrequent. For this reason, active restoration efforts are required and strongly recommended. In particular, restoration by ex situ recruitment enhancement is to be favoured. This is a sustainable and non-destructive methodology, which foresees the collection of fertile apices in a donor site, the reproduction and cultivation of propagules in mesocosm and the further outplanting of the cultivated germlings in a receiving site to be restored. In this thesis, the theme of restoration of Cystoseira forests by ex situ recruitment enhancement is addressed. The I part of the work provides base-knowledge on three Cystoseira species, useful to underpin further restoration efforts. In the first chapter, the early development of Ericaria barbatula (= C. barbatula) is described. This threatened species, particularly requiring in terms of water quality, could be a possible candidate for restoration efforts, thus the acquired knowledge could be exploited for the development of culturing protocols for ex situ recruitment enhancement. The second chapter represents the first description of the detrimental effects of a marine heatwave on the reproductive phenology of a macroalga, providing some considerations on the possible role of thermal anomalies and climate change in explaining the decline of Gongolaria barbata (= C. barbata) observed in the Gulf of Trieste (Northern Adriatic Sea) in the last thirty years, and of Cystoseira species in general. The third chapter focuses on the thermotolerance of early-life stages and adults of Ericaria giacconei (= C. hyblaea), a dotted endemism of the south-central Mediterranean Sea, discussing its conservation under ocean warming. Also the first description of the species’ embryology is provided. The II part of this work focuses on some of the first restoration efforts of Cystoseira species by ex situ recruitment enhancement in the Mediterranean Sea and the application of novel methods towards its upscaling. The first chapter reports the first restoration of G. barbata in the Adriatic Sea by ex situ recruitment enhancement, addressing the effects of the abovementioned marine heatwave and fish grazing on the restoration performance. Also in this case, the description of the species’ embryology is published for the first time. The second chapter investigates the effect of the donor population and the receiving site on the restoration performance and the feasibility of decreasing the restoration costs by reducing the cultivation time in mesocosm. This thesis contributes to the science behind the restoration of Cystoseira forests in the Mediterranean, which is still at the outset. The results obtained in the I part provide new knowledge on the biology of Cystoseira species from different parts of the Mediterranean Sea, useful to underpin future restoration efforts. In the II part, the implementation of restoration efforts shows how, despite biological and logistic challenges can be overcome, complex environmental dynamics and unpredictable climatic events represent the major threat to the success of restoration of Cystoseira s.l. forests, strongly limiting the possibilities of upscaling and the predictability of outcomes. In a context of ever increasing anomalous climatic events and environmental pressures on coastal habitats, the implementation of mitigation actions results as a crucial strategy to manage the stochasticity of restoration results.