Vertical migration, nutrition and toxicity in the dinoflagellate Alexandrium tamarense

Abstract

The effect of nitrate-N availabil~ty on paralytic shellfish toxin production by the dinoflagellate Alexandrium tamarense was studied in a vertically stratified laboratory water column (tank) where swimming behavior could influence photosynthes~s and nutrition. Results were compared with those from batch and seml-cont~nuous cultures In w h~c h migratory behavior was not a factor The batch and semi-continuous cultures demonstrated a dlrect posltlve r e l a t~o n s h~p between N avallablllty and toxln content. Steady-state cultures, maintained at 2 contrasting rates of semi-continuous N supply, also demonstrated significantly diffel-ent cellular toxin profiles (relative proportion of toxlns) The tank experiment was carried out In a 2.1 m PVC cylinder (0.29 m internal d~a m e t e r ) and lasted for 24 d. lnitially, nitrate was replete throughout the water column (50 PM) and the h~g h l y toxic cells fol-med a thin surface layer which persisted throughout the 1 4 h light:lO h dark cycle. When nltrate was depleted in the surface layer a s a result of uptake by the phytoplankton, the cells began a nocturnal migration to the nitracline. During this phase the toxln content of the cells decreased gradually a s the C : N of the cells increased. In the third phase, the deep nitrate pool bvas exhausted and the cells penetrated deeper durlng the dark period. The toxln content of the crlls reached the lowest level during this phase. When nitrate was added to the deep layer, a fourth phase began, d u r~n g which nocturnal descent of the rnigratlng cells was again restricted to the nitracline; toxicity of the cells increased and C:N declined. Finally, N was added to the surface layer. During this flfth and final phase, cellular tox~city continued to rlse, C:N declined further, and the cells continued to mlgrate to the thermocline d u r~n g the dark period. The toxicity of the cells during the N-stratified phases of the water column exper~ment was ~ntermediate between the N-replete and N-depleted phases, indicating that A. tamarense is capable of producing PSP toxins from N acquired during a nocturnal descent. It is concluded that toxic dinoflagellates inhabiting N-depleted coastal waters are likely capable of sustaining growth and a moderate level of toxicity through nocturnal migrations to deep N pools.

Analysis of phytoplankton distribution and community structure in the German Bight with respect to the different size classes

“…The higher occurrence of dinoflagellates in summer of both years is in accordance with results published by e.g., Hagmeier and Bauerfeind (1990), Peeters and Peperzak (1990) and Hickel (1998). Under stratified, oligotrophic conditions they have competitive advantages over diatoms (Fogg, 1991) because they require no silicon for cell wall formation and are able to exploit nutrient rich water near or below the thermocline due to diurnal migrations (Cullen, 1985;MacIntyre et al, 1997). Especially the genus Ceratium was frequently abundant and has contributed to biomass, which is a typical feature of the North Sea in the second half of the year (Reid et al, 1990, see also various datasets of the Helgoland Roads time series at www.pangaea.de).…”

Photoprotection mechanisms against ultraviolet radiation in Heterocapsa sp. (Dinophyceae) are influenced by nitrogen availability: Mycosporine‐like amino acids vs. xanthophyll cycle

“…Dinoflagellates swim vertically to gather sufficient light and nutrients both in the laboratory and in the natural environment (Eppley et al 1968;MacIntyre et al 1997). Thus, Heterocapsa sp., because of its capacity of movement in contrast to diatoms, can actively modulate the UV absorption through the water column, and, in combination with the ability to activate one of the photoprotection mechanisms, i.e., MAAs and the xanthophyll cycle, in the function of N availability, this species could select the favorable deep to live.…”

Mechanisms regulating large-scale seasonal fluctuations in Alexandrium fundyense populations in the Gulf of Maine: Results from a physical–biological model

“…This effectively eliminates the downstream advection of cells that would take place during their transit upward. A potentially more serious shortcoming of this simple formulation is the lack of vertical migration behavior that could allow A. fundyense to exploit nutrients present in subsurface layers (MacIntyre et al, 1997). However, recent evidence suggests that the capability for vertical migration is not universal amongst all strains of A. fundyense from the Gulf of Maine (Poulton, 2001).…”