Meccanismi di regressione e frammentazione dell’habitat nelle praterie di Posidonia oceanica

The aim of this PhD is to describe the current health status and the temporal evolution of P. oceanica meadows of Latium coast, describing their mode of regression through the analysis of the upper and lower limits position and the application of some principles and metrics of landscape ecology. Studies on landscape fragmentation have typically been conducted in terrestrial habitats, such as forests, where indices are used to quantify habitat loss and fragmentation in relation to changes in abundance and/or community structure of associated organisms (Lord and Norton 1990; Saunders et al. 1991; Opdam et al. 1993; Reed et al. 1996; Jorge and Garcia 1997; Trzcinski et al. 1999). There are numerous indices available to quantify terrestrial landscape fragmentation, yet presently there is a general consensus about the application of these indices, however no individual index can capture the full complexity of spatial patterns, multiple indices are required for analysing landscape configuration (Saura, 2002). Indices that quantify ecologically important spatial patterns are necessary for achieving the goal of landscape ecology: ‘to elucidate the relationship between landscape patterns and ecological processes’ (Turner, 1989). Although landscape indices have been also been used to quantify spatial patterns of various aquatic habitats (Bell and Hicks 1991; Irlandi 1994, 1997; Irlandi et al. 1995; Garrabou et al. 1998; Kendrick et al. 1999; Hovel and Lipcius 2001), such as seagrass. Seagrass ecosystems occur over broad spatial scales (tens to hundreds of kilometres) and are characterised by a continuum from fragmented patches to continuous meadows (Sleeman, 2005). Given the high ecological significance of seagrasses, it is necessary to define reliable measures that can be used by researchers and resource managers to identify fragmentation and quantify spatial change in relation to ecological processes (Sleeman, 2005)