have limited sexual compatibility to other species. scientists have observed hybrids of toxic and non-toxic forms produce lethal cells. alexandrium is an opportunistic dinoflagellate and thus it can bloom in nutrient-rich and nutrient-poor areas. for most species, in order for the bloom to be positively regulated it must be in a water body with high surface water temperatures, maximum water column stability, low nutrients, and low winds. in salt ponds, alexandrium population growth rates depend on salinity and temperature. however, in areas like the bay of fundy, bloom dynamics depend more readily on the mixing of tidal waters in the open region. in salt ponds, a. fundyense migrate vertically down at night, but migrate closer to the surface of the pond during the day. however, they do not migrate too close to the surface to be flushed out with the outflowing surface water. (3) the hydro-geographical barrier and the organism's behavior restrict blooms to occur in neighbouring waters, and thus, result in high concentration of toxicity accumulating in shellfish. other oceanographic forces include the mechanisms of upwelling winds and downwelling winds that can also play a role in bloom concentration. (10) upwelling winds result in pushing the cells off the coast. (10) this can decline the bloom populations. however, when wind is pushing the bloom offshore, the vegetative cells can encyst and sink to the bottom of the sediment. (10) once wind levels decrease, they transform into vegetative cells again. (3)(10) on the other hand, downwelling winds can allow the cells to be brought back to the coast and resurfaced. (10) this can have the opposite effect of localizing blooms and thereby increasing toxic concentration. (10) the time length of the blooms occur around 2–3 months. generally, warm temperatures and sufficient nutrient concentrations can provide for excellent growth. however, even with optimal temperatures, alexandrium populations can be declining and this has more to do with the life cycle than what was thought to do with things like predation and parasitism. sexuality happens well before the bloom population peaks, and a large fraction of the bloom population is mating to produce cysts that fall to the sediment. hence, experiments have shown that temperature and nutrient availability can regulate sexuality and encystment. it has been shown that a.catenella relies on organic nutrients produced by diatom blooms and or from picocyanobacterial. such observations may be a reason why blooms from other protists like diatoms correlate with blooms of alexandrium. alexandrium has been increasingly more common in large city harbours, for example along the coast of the mediterranean sea. high alexandrium growth has also been typically found in low salinity freshwater plumes. freshwater runoffs have high organic matter, and other micronutrients, such as high iron content. even though humans have definitely increased the amount of biomatter in the ocean, we cannot directly correlate an increase in range of alexandrium blooms because of human activity. this is because most blooms occur in remote and pristine waters in places like alaska and southern argentina. as autotrophs, alexandrium produces oxygen by consuming inorganic carbon. organic carbon is not excreted as much compared to other phytoplankton. inorganic carbon fixation increased or decreased either with an increase or decrease in nitrogen uptake, depending on the nutrition of the cell. alexandrium accumulates ammonium internally. many species are also mixotrophs and have been observed to contain bacteria and flagellates inside food vacuoles. a. minutum can ingest cyanobacteria. a. catenella can ingest heterotrophic bacteria and cyanobacteria. a. tamarense ingests haptophytes, cryptophytes, small diatoms, and heterosigma akashiwo. a. tamarense has also been observed eating other dinoflagellates such as amphidinium carterae and prorocentrum minimum. blooms can be terminated because of cell lysis, infection from viruses and/or bacteria, parasites, and encystment. both heterotrophic and mixotrophic dinoflagellates feed on alexandrium. as does the ciliate favella. amoebophrya (a parasitic dinoflagellate) and parvilucifera (a perkinsozoan flagellate), are known to infect alexandrium species. specifically, parvilucifer infects the mobile zygote and pellicle cyst of a. minutum. morphology and anatomy alexandrium has a typical dinoflagellate morphology, with the episome, cingulum, hyposome, and sulcus. it has two flagella: a transverse flagellum around the cingulum groove called the girdle, and the longitudinal flagellum that extends outwards from the sulcal groove. it has an ornamented theca. the morphology of alexandrium is variable but, the genus alexandrium can be separated from gessnerium by having the 1' plate directly or indirectly connected to the extreme, anterior plate, po. generally, the po is large and oval. the po has a cavity called the aperture which is mostly comma-shaped. there are many small pores on the outside of the comma and the apical plates. species that produce chains have secondary pores that are located most of the time dorsally on the comma. these pores are not found in the cingular and sulcal plates. life cycle alexandrium has a zygotic lifecycle. in the vegetative phase, the species are haploid and under certain circumstances related to stress, the vegetative cells can transform into non-motile pellicle cysts with a thin cell wall. (3) the vegetative phase and pellicle cyst stage are very flexible and alexandrium species can often switch back to vegetative cells when the stress has been removed or decreased. (3) in the vegetative phase, cells divide through desmoschisis: each daughter cell retains half the thecal plates of the mother. some species such as a. taylorii and a. hiranoi can produce non-motile dividing cysts that have the ability to divide, where the formation of these cysts are restricted to the dark phase and germination in the light phase. the triggering of pellicle cyst formation is often due to turbulence, presence of parasites, and or passage through the gut of grazers. thus, one of the defense mechanisms that alexandrium deploys against parasites, is by becoming pellicle cysts which makes them more resistant to parasitic infection. some species have evolved forming chains to give them an advantage. it is suggested that forming chains is in response to high turbulence, to swimming faster than single cells allowing them to migrate farther or deeper, and a defense mechanism for reducing grazing. during the sexual phase, the vegetative cells can form gametes that conjugate, resulting in what is called a diploid planozygote that can transform into a resting cyst called a hypnozygote. in some species, the planozygote can go through meiosis and produce a vegetative cell. the gametes can recognize each-other by the help of agglutinin-like compounds and the gametes can then fuse on their ventral side, producing a biflagellated diploid planozygote. the gametes of alexandrium are the same as vegetative cells or they can be smaller in size. the time the hypnozygote spends in the sediment is most likely related to the specific species and or environmental factors. temperature changes have also been shown to produce varying amounts of cysts. in the case of a. tamarense, specific bacteria may inhibit or trigger cyst production. in colder temperatures, the maturation length may be prolonged. the bloom of some species is seasonally driven, or the bloom can be regulated by environmental forces (e.g. temperature), in addition to being seasonally driven. under the right conditions, the hypnozygote germinates and releases a motile cell called a planomeiocyte. the sexual cycle is complete once the planomeiocyte divides and produces vegetative cells again. genetics the cell cycle is composed of the typical eukaryotic stages in m1, s phase, g1 and g2. it goes through a light/dark dependent manner. during the night, the cells are haploid and have only one copy of the dna. during the day, the population is in s phase with two copies of dna. they go through closed mitosis. g2 to m phase is regulated by nutrient factors, while the s phase is controlled through light/dark timing. alexandrium species must be of proper size before then can enter s and g2 phase. alexandrium fundyense increases greatly in size during the g2/m phase and after mitosis, it decreases in size. other species can produce dna through the entirety of the cell cycle. thus, researchers have said that going through g1 is light dependent and going through s phase is size dependent. the specific toxins produced are regulated by the nuclear genes. the genome mass is upwards of 200 pg dna. it has up to 150 chromosomes that have permanently condensed chromatin. both the plastid genome and the mitochondrial genome are typical of normal dinoflagellates. for example, in the case of plastid genomes, the number of plastid genes have reduced because they have become nuclear encoded instead. in a. tamarense, researchers have identified 48 non-minicircle encoded photosystem genes which are found in the nuclear genome. 15 genes that are supposed to be found in the plastid genome have become nuclear encoded instead in a. tamarense. hence, the plastid genome has been reduced to 15 single-gene minicircles. the mitochondrial genome is also greatly reduced to only having cob, cox1, and cox3 protein coding genes. they also have lost the complex 1 oxidative phosphorylation genes and a. tamarense has replaced it with nadh dehydrogenase 2 (ndh-2). in the case of a. catenella, translation of the mitochondrial genome, does not require initiation and termination codons. fossil record although alexandrium does not fossilize very well. the resting cysts can fossilize somewhat. some researchers have hypothetically calculated that the average age of alexandrium is 77 million years old which is going back to the cretaceous period. what allowed alexandrium to increase greatly was the mass extinction in the cretaceous period (65 mya) and the great increase in temperature of the sea in the paleocene era (55 mya). these two events reduced alexandrium competitors and also made it more favorable for it to increase in size. the rise of the isthmus of panama that happened between 3-13 mya subdivided and separated many species into distinct geographical populations. this had profound effect on the alexandrium tamarense species complex. in the present day, their population is much smaller than what was before. practical importance alexandrium produces a variety of toxic derivatives. the first group of toxins it produces includes carbomoyltoxins: saxitoxin (stx), neosaxitoxin (neo), and c-11 o-sulfated analogues gonyautoxins (gtx1-gtx4). the other group of toxins made is the n-21 sulfocarbamoyl analogues (b1=gtx5, b2= gtx6, c1-c4). toxin production seems to be genetically specific in the different alexandrium species, but the cell toxin content is much more variable and thus, not a very good molecular marker for phylogeny. however, it seems that with distinct geographical locations, there may be differences in the psp toxin composition of alexandrium species or even strains. there may be selective forces that favour certain cysts with particular toxin composition. psp toxin is produced in the g1 phase of the cell cycle and spirolides are produced in the g2 phase of the cell cycle. specific polyketide (pks) genes are involved in spirolide biosynthesis. spirolide is composed of acetate with an imine moiety. the saxitoxin pathway is generally the same in dinoflagellates and cyanobacteria, but the transcripts of the dinoflagellates occur in multiple copies, meaning it is monocistronic, and have splice leader sequences. lytic allelochemicals target external cell membranes of other protists. in particular, lytic compounds in a. tamarense can increase the permeability of ca2+ ions in other protist cell membranes. waterborne cues from copepods can upregulate psp toxin content in alexandrium and differentially regulate genes by regulating the serine/threonine kinase signalling transduction pathway. alexandrium blooms cause psp poisoning in bivalve molluscs, but they can also cause damage to fish farms resulting large losses local or large businesses. many salmon are affected every year in canada because of alexandrium blooms. a. catenella can cause low gill viability. a. catenella causes tissue damage in gills, by primarily producing reactive oxygen species or ros.