State of posidonia oceanica meadows around the sardinian coast

In order to assess and control marine pollution along the coastal strip, a project focused at monitoring and mapping Posidonia oceanica meadows all around the Sardinian Island (Central Western Mediterranean Basin) was founded by the Italian Government in 2001. More than 300,000 biological data were collected along 1800 Km of coast line, in the bathymetric range between 5 and 40m. Due to the amount and nature of Posidonia descriptors (both structural and functional, both at molecular and system level), a specific data warehousing approach was performed. Datamining techniques allowed to choose a preliminary set of values, related to long term (1969-1998) annual plant production, derived by lepidochronology, such as rhizome production, rhizome elongation and leaf production. Selected data were analyzed by Autoclass C for determining the number of classes. Two different classes of plant production were obtained, called 'High' and 'Low' respect to regional annual mean; their centroids did not vary between shallow and deep stands (between 5 and 10m and between 22 and 28m depths, respectively). The highest production values (90.1 mg/rhizome/y, 11.44 mm/rhizome/y, 7.7 nr. leaves/y) characterized the shallowest stations. Only one class was identified for the stands on the deepest limit (more than 35m depth) (37.32 mg/rhizome/y, 5.37mm/rhizome/y, 7.6 nr.leaves/y). A class analysis for each station showed a clear regional zonation: A north-east sector, with the lowest plant production, a south-east sector with the highest ones, and a north-west sector, with intermediate plant growth rates. According to these results, a functional classification of sardinian meadows was attempted. The correspondence between functional (based on production values) and structural (based on density values) classifications seemed to reflect different levels of anthropogenic disturbance forcing on Sardinian coastal line.