The use of principal component analysis in phytoplankton data: comparison of communities at one coastal station in the Gulf of Trieste

The phytoplankton succession in the Gulf of Trieste, during the autumn, winter and spring of the years between 1986-1988, is analyzed by means of multivariate statistics to describe the temporal sequence of variation and the population groups. The principal component analysis gives the temporal dynamics of the data set considered and the cluster analysis identifies the groups of species dominant in each season. The typical Diatoms -Dinoflagellates succession is recovered, while no significant variation in the structure of the community in the water column in each year data is identified. The between-year variation, which occurs in the species describing the temporal-evolution in the community, is highlighted. This between year species replacement suggests combining the classical principal component-cluster analysis with a rotation of the principal components. An orthogonal Procrustes transformation is applied both to sampling units and to species groups. It recovers the same underlying pattern as in the multi-annual succession of communities described at species level.