Abstract
Posidonia oceanica is an endemic Mediterranean seagrass used as a ‘biological quality element’ in monitoring programmes of the EU Water Framework Directive, providing information about coastal ecosystems status. The regression of P. oceanica meadows caused a growing interest among policy makers to assess the value of seagrasses and to increase their protection. An evaluation of P. oceanica meadows located in the Ligurian-Provençal basin (NW Mediterranean) through a biophysical approach is here developed. Six meadows located in Liguria (Italy) and Corsica (France) were investigated by applying the emergy analysis to assess the natural capital (NC) stocked by leaves and rhizomes components. Results highlighted the importance of carrying out an analysis of the variations in the NC value in both components: rhizomes defined the growth stage and the capacity to store NC over time; leaves provided information on the variability due to disturbances in the water column. Emergy analysis allows defining the NC, in terms of resources needed to maintain the meadows and to provide services to coastal communities. This research is inserted into the effort of incorporating the NC evaluation into marine planning and decision making to achieve nature conservation goals, while ensuring the sustainable exploitation of marine resources.
Highlights
Marine coastal ecosystems are among the most productive ecosystems in the world [1,2], and they are able to provide a series of ecosystem services vital to human well-being [2,3], such as food provision, coastal protection against storms and floods, water purification, nutrients cycling, carbon sequestration, tourism and recreational and spiritual benefits [4,5,6,7].The entire stock of natural assets that make up these ecosystems represents the natural capital [3,8]
The model of natural capital assessment that was followed consists of three main steps: (1) trophodynamic analysis; (2) biophysical accounting (estimation of the biophysical value of natural capital that support the biocenosis in terms of emergy associated with the natural resource flows that enabled the formation of the natural capital stock); (3) monetary conversion
It is recognised that structurally damaged ecosystems have little resilience: the low shoot density values, recorded in Prelo-San Michele meadow, indicate that here P. oceanica is far from the good status and optimum vigour that lie behind ecosystem health [16,102,113] even if its growth mature stages have allowed it to accumulate a lot of natural capital over time
Summary
Marine coastal ecosystems are among the most productive ecosystems in the world [1,2], and they are able to provide a series of ecosystem services vital to human well-being [2,3], such as food provision, coastal protection against storms and floods, water purification, nutrients cycling, carbon sequestration, tourism and recreational and spiritual benefits [4,5,6,7]. P. oceanica meadows constitute a substantial part of natural capital providing a range of ecosystem functions and services for human well-being. For this reason, this seagrass has a very important role under both ecological and economical views [21,22,23,24]. The considerable leaf biomass that characterizes meadows reduces hydrodynamic energy, preventing shoreline erosion [26] and promoting the sedimentation of particulate matter, which results in an increase of water transparency [24] Despite this species being one of the main targets of conservation actions, the regression of P. oceanica meadows is well-documented over the whole Mediterranean basin and mainly in the north-western sector [26,27,28,29,30,31].
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