Spatial variation in Posidonia oceanica structural, morphological and dynamic features in a northwestern Mediterranean coastal area: a multi-scale analysis

Knowledge of the natural pattern of spatial variation of the variables of interest is fundamental for designing effective sampling strategies to be used in surveys and monitoring programs. Unfortunately, little is known on patterns of spatial variation of structural, morphological and dynamic features of Posidonia oceanica, despite their increasing use as indicators of the status and/or trend of meadows. Here, variations in some such features (such as shoot density, leaf biometry, annual rhizome elongation and leaf formation) were examined on a hierarchy of spatial scales, ranging from cm within individual meadows, to meadows separated by 10 km, using independent full-nested analyses of variance. Overall, at least 3 variables showed significant variations in the mean values on each of the scales examined. Patterns of variability differed among individual traits. Most of the total variation, however, was on the smallest spatial scale examined (i.e. among replicates, shoots or quadrats). For some variables, a significant variation was also associated with the largest scale (i.e. among meadows). Collectively, the results indicated that patchiness in density, morphology and growth exists on a very local scale within R oceanica meadows along the same isobath. This suggests that sampling designs and analyses which incorporate different spatial scales and appropriate replications should at least be considered in the future when planning large-scale and long-term surveys