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 (μ) 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 μ from vertical net-haul (integrated) samples (μ int ) were compared with those from a single depth (oceanographic bottle samples) (μ z ) at the cell maximum during 2 daily cell cycle studies in the Galician Rías Baixas (NW Spain). Additionally, vertical profiles of μ z were obtained during a field survey in Ría de Vigo. A 2-fold difference was observed between estimates of μ z from the cell maxima and μ int from integrated samples under stratified conditions. Differences were much larger when the minimum estimates of μ values from different depths (μ 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 μ 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.KEY WORDS: Dinophysis spp. · Cell cycle · In situ division rate · Mitotic index · Cell maximum · Modelling approach Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 385: [87][88][89][90][91][92][93][94][95][96] 2009 and place, will be observed at its optimum depth in the water column, i.e. the depth where the combination of environmental conditions (resources and physicalbiological interactions) are the most suitable for that species' growth and survival.Dinophysis spp. and other toxin-producing algae (TPA) species that transmit toxins through the food web -even at moderate to low concentrations (10 2 to 10 3 cells l -1) -often constitute a small percentage of the total phytoplankton community. Bulk measurements using chemical indicators such as chlorophyll a concentration and primary production are unsuitable for growth studies of these rare TPA species since they reflect the physiology not of the target organisms but of the whole plankton community. Estimates of μ from in situ cell cycle studies are time-consuming, but provide realistic information on the division capabilities of the species in question (Reguera et al. 2003).Estimates of μ in field populations of Dinophysis spp. have been obtained either from incubations, on deck or in diffusion chambers (Garcés et al. 1997) or from direct in situ high frequency sampling with a mitotic index approach (Table 1). Dinophysis spp. often exhibit sharp heterogeneities in their vertical distribution (reviewed in , Velo-Suárez et al. 2008. To minimize sampling uncertainties derived from low cell concentrations, vertical migration or patchiness (which would result in samples with inadequate numbers of target cells), in situ ...

Seasonal and intratidal distribution of Dinophysis spp. in a Chilean fjord

“…acuminata often exhibits sharp heterogeneities in their vertical distribution (Velo-Suá rez et al, 2008). Factors such as advection, usually described as the most important factor in dinoflagellate accumulation during downwelling conditions, and in situ growth, may have caused an increment in D. acuminata concentrations as observed by Velo-Suá rez et al (2009). Others researchers have suggested that the diurnal variability observed in Dinophysis spp.…”

Harmful Dinophysis species: A review

“…Several species of Dinophysis have been observed to exhibit in phase cell division in field populations from different temperate regions (Campbell et al, 2010;Farrell et al, in press-b;Velo-Suá rez et al, 2009 and references therein). Cell division is maximal in early morning.…”

“…have been considered slow-growers by some authors (Smayda and Reynolds, 2001;Stolte and Garcé s, 2006). Nevertheless, field observations have shown that different species of Dinophysis observed during different stages of their population growth and under distinct environmental conditions can exhibit a wide range of values in m gross , between practically zero and as high as 1 division per day (m gross = 0.69 d À1 ) (see Table 1 in Velo-Suá rez et al, 2009;Farrell et al, in press-b). Therefore, in field conditions Dinophysis spp.…”

Bloom dynamics of Dinophysis acuta in an upwelling system: In situ growth versus transport

“…Further, in the case of Dinophysis spp., that usually constitute only a small (<5%) percentage of the microplankton assemblage, bulk measurements using chemical indicators, such as chlorophyll a concentration or primary production, and conventional cell counts, are unsuitable to follow the bloom dynamics (Reguera et al, 2003;Velo-Suá rez et al, 2009).…”