Migraciones verticales de Alexandrium excavatum (Braarud) Balech et Tangen en columnas experimentales

Abstract

• Abstract: Diel vertical migrations of the marine dinoflagellate A. excavatum were followed in a laboratory water column, and the effects of temperature stratification and nitrogen depletion on patterns of migration were examined. It was found that A. excavatum is a vertical migrator aggregating at surface durlng daylight, and descending at night. A six-degree thermocline did not restrict its migration but delayed the vertical movements. Nitrogen depletion in the culture was correlated with earlier downward migration in the day, and nitrate assimilation in the dark was confumed In another essay, with a nitrogen deficient culture, nocturnal nitrate uptake per cell was measured. It is suggested that the ability ofA. excavatum to take up nitrate in the dark working together with diurnal vertical migration could be important mechanisms regulating bloom developments.

Vertical migration, nutrition and toxicity in the dinoflagellate Alexandrium tamarense

“…Although it was previously demonstrated that a European strain of Alexandrium tamarense could migrate across steep pycnoclines (Rasmussen & Richardson 1989) and thermoclines (Santos & Carreto 1992), a marked die1 pattern of vertical migration had yet to be confirmed in t h~s toxin-producing species. This study demonstrates for the first time that.…”

“…Thus, N-stratified coastal waters with a steep thermocline provide an environment which is suitable for bloom formation by vertically migrating dinoflagellates. Although the toxic dinoflagellate Alexandrium tamarense does not reach high standing stocks generally, it is known to form dense near-surface populations in coastal waters (Sakshaug & Jensen 1971, Anderson & Stolzenbach 1985, Iwasaki 1989, Carretto et al 1990, Esteves et al 1992, Rensel 1993) and has demonstrated directed swimming ability in laboratory conditions (Rasmussen & Richardson 1989, Santos & Carreto 1992; consequently, we hypothesize that this species has the ability to migrate vertically to deep pools of nitrogen. Given the effects of nutrition on the toxicity of A.…”

Physiological and behavioral diagnostics of nitrogen limitation for the toxic dinoflagellate Alexandrium fundyense

“…To date many adaptations have been identified within natural phytoplankton communities, some behavioral and some physiological. In the former category, it has long been recognized that motility behavior of marine phytoplankton allows them to migrate through temperature gradients and exploit sources of sub-surface nutrients in the field (Eppley and Harrison 1975;Blasco 1978;Anderson and Stolzenbach 1985;Passow 1991) and the laboratory (Eppley et al 1968;Kamykowski and Zentara 1976;Cullen and Horrigan 1981;Cullen et al 1985;Rasmussen and Richardson 1989;Santos and Carreto 1992;). …”

“…To date Alexandrium species have exhibited migration behavior across steep pycnoclines (Rasmussen and Richardson 1989), temperature (Santos and Carreto 1992) and nutrient ) gradients, and for decades the influence of N-nutrition has been associated with migration patterns for many dinoflagellates in both the laboratory and the field (Eppley and Harrison 1975;Blasco 1978;Cullen and Horrigan 1981;Kamykowski et al 1999). During a study by , Alexandrium tamarense from the Gulf of St. Lawrence was capable of migrating across thermoclines in order to exploit deep nitrogen pools when induced by low N concentration in surface waters.…”

Plankton and particle biomass size spectra on the Southwest Atlantic: Case studies in tropical and subtropical areas

“…This species only showed its nocturnal migrations when nitrate was depleted from the surface; this kind of behavior was also described for other species (e.g., Santos and Carreto, 1992). hence even phytoplankton species with lower motility, such as diatoms, could also be favored by nutrient input during intrusions.…”