Can Pseudo-nitzschia blooms be modeled by coastal upwelling in Lisbon Bay?

Marine planktonic diatoms of the genus Pseudo-nitzschia Peragallo have been responsible for amnesic shellfish poisoning (ASP) events worldwide through the production of the neurotoxin domoic acid (DA). In order to better understand the dynamics of the toxic events of Pseudo-nitzschia there is the need to describe their seasonal and spatial patterns. The main goal of this work is to establish the relation between a physical variable easily measured like coastal upwelling and the presence of Pseudo-nitzschia blooms, in Lisbon Bay. Phytoplankton samples were collected once a week from June 2001 to May 2005 and daily upwelling index were calculated based on values of geostrophic winds. Data of sea surface temperature, upwelling index, and Pseudo-nitzschia concentrations were used to construct statistical models to evaluate the seasonal variation and the relation between all parameters. Due to the nature of the time series involved in the study, it was applied the Zero-Inflated Generalized Poisson Regression Model. An initial spectral analysis was applied to the upwelling data in order to accurately understand the characteristics of the coastal upwelling. The results obtained indicate a close relation between upwelling events and Pseudo-nitzschia blooms which occurred during spring and summer. The mathematical model that describes Pseudo-nitzschia blooms in Lisbon Bay shows a lag of 4–6 days between the upwelling events and the presence of Pseudo-nitzschia in the monitoring station.