Vertical distribution of the chloromonad flagellate Heterosigma carterae in columns: implications for bloom development

Abstract

Blooms of the marine flagellate Heterosigma carterae have been associated with catastrophic fish kills at mariculture facilities around the world. The precise cause(s) of the sudden appearance and disappearance of Heterosigma surface blooms has not been completely described or understood. Environmental data from prior studies of blooms indicate the presence of vertical stratification of the water column that is often induced by freshwater runoff. We report the relatively rapid concentration of Heterosigma cells at the surface of tubes shortly after the addition of distilled water to the surface. This phenomenon of cell concentration in surface waters may partially explain the sudden appearance of Heterosigma cells near the surface and subsequent disappearance when vertical stratification is lost due to turbulence or mixing. The results may lead to bloom mitigation techniques for net pen aquaculture.Résumé : Des poussées de flagellés marins (Heterosigma carterae) ont été associées à de catastrophiques mortalités massives de poissons dans des installations de mariculture à divers endroits du monde. Les causes exactes de l'apparition et de la disparition soudaines des efflorescences d'Heterosigma en surface n'ont pas encore été clairement définies, ni bien comprises. Des données environnementales provenant d'études antérieures révèlent la présence d'une stratification verticale de la colonne d'eau, souvent liée à un apport d'eau douce. Nous avons enregistré une augmentation relativement rapide de la concentration de cellules d'Heterosigma à la surface des éprouvettes peu après l'ajout d'eau distillée à la surface. Ce phénomène de concentration de cellules dans les eaux superficielles pourrait expliquer en partie l'apparition soudaine de cellules d'Heterosigma près de la surface, puis leur disparition lorsque la stratification verticale s'efface en raison de la turbulence ou du brassage. Les résultats de l'étude pourraient servir à élaborer des techniques d'atténuation des efflorescences qui seraient utiles à l'aquaculture en parcs de filet. [Traduit par la Rédaction]

Effects of salinity on diel vertical migration behavior in two red-tide algae, Chattonella antiqua and Karenia mikimotoi

“…The presence of low-salinity surface layers strengthens vertical stability of the water column, which promotes cell accumulation by DVM and thereby increases the likelihood of red tide formation by flagellates (Hershberger et al 1997). Red tides of C. antiqua and K. mikimotoi also develop under stratified conditions originating from river inflow (Yamaguchi 1994, Matsubara et al 2009).…”

A novel Heterosigma akashiwo (Raphidophyceae) bloom extending from a South Carolina bay to offshore waters

“…The average water discharge increased from about 10,000 ft 3 s À1 in both January and February to approximately 45,000 ft 3 s À1 in both March and April (courtesy of USGS). Hershberger et al (1997) reported that Heterosigma cells concentrate in surface regions of lesser salinity water. Surface salinity measurements during the bloom were 21.3 psu, significantly less than the average salinities for the area (32.5 AE 2.8 psu).…”

Effects of Heterosigma akashiwo (Raphidophyceae) on protist grazers: laboratory experiments with ciliates and heterotrophic dinoflagellates

“…H. akashiwo is distributed globally in euryhaline, coastal environments, and high cell concentrations are often associated with low-salinity sea surface layers (Honjo 1993, Taylor & Haigh 1993, Hershberger et al 1997.…”