Application of ordinal correspondence analysis for submerged aquatic vegetation monitoring

<italic>The European Water Framework states that macrophyte</italic> communities (seaweeds and seagrass) are key indicators of the ecological health of lagoons. Furthermore, the restoration of these communities, especially the <italic>Zostera</italic> meadows, is one of the main objectives of the Berre lagoon restoration plan. Consequently, a monitoring programme of the main <italic>macrophyte</italic> species still present in the lagoon was initiated in 1996. This monitoring resulted in a sequence of 11 spatially structured annual tables consisting of the observed density of these species. These tables are processed in this study. First, we specify the principles of Beh's ordinal correspondence analysis (OCA), designed for ordered row/column categories, and compare this method to classical correspondence analysis (CA). Then, we show that OCA is straightforwardly adaptable for processing a sequence of ordered contingency tables like ours. Both OCA and CA are afterwards used to reveal and test the main patterns of spatio-temporal changes of two <italic>macrophyte</italic> species in the Berre lagoon: <italic>Ulva</italic> and <italic>Zostera</italic>. The results we obtained are compared and discussed.