Shoot micro-distribution patterns in the Mediterranean seagrass Posidonia oceanica

Posidonia oceanica meadows host a huge number of shoots and their dynamics is strictly related to the spatial distribution patterns of those shoots. To investigate the structure of P. oceanica meadows at very small spatial scale (i.e. in the 100–102 cm range), point patterns of shoot micro-distribution were analyzed. Spatial distribution of shoots was recorded by cutting all the leaves and by digitizing shoot location from pictures of square frames (1 m2) that were randomly positioned in seemingly uniformly dense stands. Ten frames were sampled, all from Southern Italian meadows, and the position of 7828 shoots was recorded. Nearest neighbour distance (NNd) statistics revealed recurring patterns at the different spatial scales: regular patterns were recognized among shoots at smaller spatial scale (100–101 cm), while aggregated shoot distribution emerged in the 101–102 cm range and an important stochastic component was observed at larger spatial scales. Reasons underpinning different spatial point patterns in P. oceanica meadows were discussed by relating the observed patterns to ecological processes (i.e. competition among shoots, role of “species-specific” drivers or “site-specific” features), also including relationships between shoot NNd and shoot density counts. The raw data, provided as supplementary material, are currently the first and the only source of information available about shoot spatial micro-distribution. In this regard, although our data set cannot represent the whole spectrum of variability in P. oceanica meadows, it can be regarded as a first step towards a better knowledge of small scale shoot point patterns in P. oceanica meadows.