On the presence of Pseudo-nitzschia calliantha Lundholm, Moestrup et Hasle and Pseudo-nitzschia delicatissima (Cleve) Heiden in the Southern Adriatic Sea (Mediterranean Sea, Italy)

This investigation included a 2-year monitoring program aimed at assessing the abundance and distribution of harmful marine phytoplankton along the Southern Adriatic coast of Italy. Monthly sampling was conducted from April 1995 to March 1997 at four sampling stations along four transects, to determine the temporal and spatial presence/abundance of the potentially toxic Pseudo-nitzschia species. The study focussed on the most abundant taxa Pseudo-nitzschia calliantha and Pseudo-nitzschia delicatissima, the identities of which were confirmed by TEM on cleaned net material. The distribution patterns of these potential Amnesic Shellfish Poisoning (ASP) toxin producers were statistically analysed by Generalised Linear Model ANalysis Of VAriance, Principal Component Analysis (GLM ANOVA, PCA) and Spearman's correlation analysis in order to address relationships between environmental variable and population dynamics. Abundances displayed horizontal and vertical structure in the study area. Inter-annual variability was also observed for both species that appeared to respond differently to the environmental factors investigated. Distributions of P. calliantha showed a stronger seasonality and was more correlated with winter water conditions than P. delicatissima, which in turn exhibited a broader temporal distribution and appeared independent from major environmental constraints. This is the first report of the occurrence and dynamics of P. calliantha and P. delicatissima populations in Southern Adriatic coastal waters.