A simple short range model for the prediction of harmful algal events in the bays of southwestern Ireland

A simple model is described which predicts harmful algal events in the bays of southwestern Ireland. Fundamental to the model is the physical forcing of circulation in these bays in summer. The predominant hydrographic feature at this time is a wind-driven two-layer oscillatory flow acting in a thermally stratified water column. This mechanism exchanges substantial proportions of the bays' volumes, and harmful algal events arise with the associated transport of harmful populations into them. The model is therefore based on the criterion that wind-driven water exchanges result in exchanges of phytoplankton, which, if the time of year is correct, result in toxic events. Utilising Bantry Bay as an example, hindcasting showed that the model has a high degree of success using a wind index based on the sequence of winds that results in water exchange. The model was implemented by estimating indices from the five-day weather forecast, and trialled in 2005. Results were published on the web in real time, during which a predicted water exchange event in mid-June was accompanied by an influx of Dinophysis acuminata into Bantry Bay with an associated contamination of shellfish with Diarrheic Shellfish Poisoning toxins.