We consider the possible extent to which dinoflagellate cyst-bed dynamics contribute to the seemingly unpredictable pattern of HAB occurrence. The following are defined: Population of motile cells in the bloom (MP1), initial population of cysts produced by MP1 (ICP), the viable cyst population from ICP (VCP) producing a new motile population (MP2), and the size and shape of the sedimentary system within which viable cysts may be transported (SS). Three basic "bloom strategies" are suggested: 1) HAB species without resting cysts (e.g. Gymnodinium breve in Florida) - MP2 is residual from MP1 surviving in the water column, independent of the sedimentary regime; 2) HAB species heavily dependent on seed beds (e.g. Alexandrium tamarense in higher latitudes) - these are most affected by the sedimentary regime where environmental factors can be identified at all stages with potential for producing greatly different values for MP2 from the same sized MP1 and SS; well suited to restricted parts of coastal environments (e.g. fjords, bays) with the closest possible isolation of discrete combinations of water bodies and sedimentary regimes, and with marked seasonality where cysts with long mandatory resting periods act as important over-wintering stages; and 3) (recognized from our observations of changes since 1995 in cyst assemblages in a newly constructed harbour on the otherwise exposed southwestern coast of Portugal) HAB species that produce large amounts of cysts but seemingly independent of seed beds (e.g. Gymnodinium catenatum along the southwestern coast of Europe/northwestern coast of Africa) - cysts probably excyst within a few days of formation, leaving only large amounts of empty cysts and non-viable cysts in sediments; probably function as category 1 above despite cyst formation. For categories 1 and 3, long term monitoring (> 30 years) offers the possibility to identify determining factors in hydrological and meteorological conditions (Stumf et al., 1997) that should help with HAB predictions. For category 2, cyst-bed dynamics need to be considered as an important scource of variance not usually accounted for (Eilertson & Wyatt, 1997), but this study suggests the need for better understanding of sedimentary processes than has been applied so far.