A review of the biophysical interactions relevant to the promotion of HABs in stratified systems: The case study of Ireland

The biophysical interactions involved in the promotion of harmful algal events are reviewed with specific reference to events that have occurred around Ireland. The direct and indirect effects of tides, solar heating and winds are considered over a range of length scales from ca. 10⁵m down to <10m. For example the effects of tidal mixing across the continental shelf through to tidal flushing of embayments is discussed in relation to the distribution and timing of harmful algal events. The effects of winds in moderating coastal currents and also forcing exchanges between water in bays and that on the adjacent shelf are also described. Similarly, the consequences of the annual cycle of thermal stratification of the water column on the promotion of harmful algal events are illustrated over a range of temporal and spatial scales. These include the timing of a harmful event (seasonality) down to physical effects associated with sub-surface high-density thin layers of harmful species. The application of bulk models for predicting harmful events based on a thorough understanding of the physical promotion of the mechanisms involved is discussed.