Vertical distribution of division rates in coastal dinoflagellate Dinophysis spp. populations: implications for modelling

Abstract

This study explores vertical heterogeneities of in situ division rates (mu) of 3 species of Dinophysis and discusses its implications in modelling the population dynamics of these species. Based on a post-mitotic index approach, estimates of mu from vertical net-haul (integrated) samples (mu(int)) were compared with those from a single depth (oceanographic bottle samples) (mu(z)) at the cell maximum during 2 daily cell cycle studies in the Galician Rias Baixas (NW Spain). Additionally, vertical profiles of mu(z) were obtained during a field survey in Ria de Vigo. A 2-fold difference was observed between estimates of mu(z) from the cell maxima and mu(int) from integrated samples under stratified conditions. Differences were much larger when the minimum estimates of mu values from different depths (mu(min)) were compared within single vertical profiles. An exponential growth model was applied to Simulate the dynamics of a D. acuminata population during a daily cycle in June 1994. Results show that actively dividing cells of a target. species may be restricted to narrow layers of the water column. Estimates of mu at different relevant depths during cell cycle studies may be key to determining whether if increased numbers of a target species are due to in situ growth or to the balance of imports and exports.