Phased cell division, specific division rates and other biological observations of Dinophysis populations off the south coast of Ireland

Abstract

The proportions of viable cells ofDinophysisspp. that were paired (dividing) and recently divided during a cell cycle were measured on populations ofD. acutaandD. acuminataobserved off the south coast of Ireland in July 2007 and July 2009. Both species exhibited phased cell division in 2009 with maximum frequency of division (fmax) 2 h after sunrise. Different patterns of division (timing offmax) were shown by D. acutain 2007, when the population aggregated in a thin layer was transported by a coastal jet flow. High resolution (decimetre-scale) profiles within the thin layer showed large differences in the vertical distribution of biological properties (feeding status, mortality). Values of the specific growth ratemwere compared to estimates derived in similar fashion from observations onDinophysispopulations elsewhere. Different patterns exhibited by the same species in different regions may be attributed to adaptations to latitudinal differences (length of photoperiod). The question of whether phased cell division always occurs inDinophysispopulations, and the incorporation of the potential specific division rate into models of Dinophysisgrowth are discussed. Comprehensivefield data sets demonstrate the impact of the results on the coherence of Dinophysispopulations during their transport along the Irish coast in jet-likeflows towards sites of intensive shellfish culture