Valutazione del capitale naturale associato alle foreste di Ericaria amentacea

In the Mediterranean Sea, brown macroalgae of the genus Cystoseira sensu lato (Fucales, Phaeophyceae, hereafter Cystoseira s.l.) form dense forests in subtidal and intertidal rocky habitats, playing a crucial role as ecosystem engineers by sustaining biodiversity and contributing to biogeochemical cycles. In the last four decades, these macroalgae have undergone a substantial and widespread regression, because of local and large-scale anthropogenic pressures and global climatic stressors. Despite their importance for the functioning of the coastal ecosystems, baseline knowledge about Cystoseira s.l., and in particular of Ericaria amentacea, is still scarce, limiting effective conservation and management strategies for this pivotal habitat former. In addition, nowadays there is a growing interest in the quantification of ecosystem relevance through assessments of the natural capital, aim to raise awareness of the public about the protection of biodiversity and to clarify the strict relationship between ecosystems and human wellbeing. In this doctoral dissertation, the theme of the estimate of the natural capital stocked in E. amentacea forests is addressed. The first part of the thesis aimed to increase the knowledge of this species, and to collect useful information for the assessment of natural capital through the emergy analysis. Spatial and temporal variations of biomass and key attributes of E. amentacea (e.g., biomass, total organic carbon and nutrient tissue contents) were studied in order to provide a large set of data that may help future research to improve our understanding of the contribution of this macroalgae to the functioning of coastal ecosystems. Also, the effects of full protection within Marine Protected Areas on E. amentacea stands have been assessed, to shed light on the effectiveness of full protection in the preservation of this habitat. The high local-scale variability of all the investigated functional trait variables found in the study areas suggests that quantifications of functional performances of these forests over large spatial scales should rely on data from multiple sites, and that the information of key functional traits of Cystoseira s.l. species cannot be limited to sporadic, spatially limited assessments. Results also highlighted that the major role of these macroalgae can relates to carbon flows within coastal ecosystems rather than to carbon sequestration, so that they can be crucial for carbon supply towards neighboring areas and even deep systems. Such findings reinforce the need for adequate efforts to protect these marine forests and reverse their decline in the basin. However, current protection regimes within MPAs might be not sufficient, as several studies carried out in the Mediterranean Sea have pointed out and confirmed also from the analysis of E. amentacea stands performed in this study. From a more practical point of view, increasing the baseline knowledge of E. amentacea has led to an accurate estimate of the natural capital stocked in this habitat. Results, expressed in both biophysical and monetary value, through the application of emergy analysis, filled the information gap about the natural capital values of these environments. Moreover, considering the macroalgae natural biomass turnover, allowed to obtain a more detailed analysis and to assess the real value of E. amentacea highlighting its pivotal role in being a value keeper and catalyst, that is even more important in the intertidal, where conditions for life are extremely difficult. The present work will contribute to increase the knowledge of key species traits and to achieve more accurate assessments of ecosystem goods, services, and the overall natural capital associated to brown macroalgae forests, which are essential to support policy makers in refining and implementing effective management strategies that could preserve the important ecological role of these species for the functioning of coastal ecosystems.