Alexandrium tamarense

The species now known as Alexandrium tamarense was first described by Lebour in 1925 from the Tamar River in southern England under the basionym Gonyaulax tamarensis Lebour. During the 20th century, the taxon moved through several taxonomic placements including Gonyaulax tamarensis, Protogonyaulax tamarensis, and Gesserium tamarensis, before being classified under the name Alexandrium tamarense (Lebour) Balech in 1995. This framework shaped most of the older literature on bloom dynamics, distribution, and shellfish toxicity. Studies on bloom ecology demonstrated that salinity, temperature, nutrient availability, freshwater input, stratification, and meteorological conditions also help shape bloom development. Methods for tracking blooms include thecal plate staining, repeated cell counts, and long-term monitoring linked to environmental data. At the same time, work on saxitoxin, paralytic shellfish poisoning, and bloom impacts showed that Alexandrium tamarense has major ecological, public-health and economic significance. == Morphology ==

Cell structure Alexandrium tamarense is a thecate dinoflagellate, and like other species in Alexandrium , it has an armoured cell covering composed of cellulose plates arranged in a characteristic pattern. Even so, those ultrastructural studies are still important because they provide the clearest descriptions of the internal organization during the resting stages and show how stringly cyst morphology varies from vegetative morphology. Because the available evidence comes from relatively few studies, the biological significance of these bacteria remains unresolved. == Phylogenetics ==

Ribosomal markers, especially LSU, SSU, and ITS regions, played a central role in taxonomic reinterpretation of the historical Alexandrium tamarense complex because they showed that the traditional morphospecies did not form discrete monophyletic groups. Gene level analysis provided a functional perspective on interpretation of the complex. Stüken and colleagues showed that saxitoxin related genes such as sxtA are encoded in the nuclear genome rather than only in associated bacteria. They also found strong overall agreement between the presence of genomic sxtA and saxitoxin production, although they noted a few strains identified at the time as A. tamarense in which sxtA was detected but toxin was not. Those strains predate and therefore do not necessarily follow the 2014 revision, they should be interpreted cautiously when discussing the modern concept of A. tamarense. == Lifecycle ==

There are nine stages in the lifecycle of Alexandrium tamarense with transitions throughout the lifecycle between asexual and sexual reproduction. The first stage is the replication of vegetative motile cells through binary fission. Transforming into a dormant cyst allows Alexandrium tamarense to endure harsh environmental conditions that would negatively impact vegetative growth., other heterotrophic dinoflagellates such as Oxyrrhis marina, Gyrodinium dominans, Polykrikos kofoidii, and Strombidinopsis spp. , as well as larger zooplankton, such as copepods (Calanus helgolandicus, Acartia clausii, and Oithona similis). In the open ocean, these grazers play the important role of regulating the growth of A. tamarense populations, preventing overgrowth and eutrophication as well as potential toxin blooms. However, it has been found that many Alexandrium species respond to grazing cues with elevated toxin production of their own, in an apparent defense mechanism. These cues and responses, however, are species-specific and cannot be generalized for the grazer community as a whole. For A. tamarense, this has led to something of an evolutionary arms-race, wherein some copepod grazers appear themselves to have developed an immunity to saxitoxin to continue their grazing without consequence. The effect of saxitoxin varies significantly between species, with some shellfish having very rapid detoxification times while others can retain dangerous levels of saxitoxin for months to years. Ecologically, the implications of an A. tamarense bloom and the injection of saxitoxin into the foundation of ecosystems can have drastic effects on food webs in general. In zooplanktivore populations of fish, filter feeders, and even whales, as well as their predators, even low levels of toxicity in primary consumers can accumulate and have serious, even lethal consequences. In July 1976, a massive kill of herring was determined to have been caused by A. tamarense toxicity, with repeat incidents identified with markedly fast mortality from toxins accumulated through zooplankton grazing. In the St Lawrence Estuary, a 2008 bloom of A. tamarense was linked to mass mortality of beluga, seals, porpoises, birds, and fish. The potential for loss of predator populations has the potentially to completely reshape marine systems and food web dynamics. == Geography ==

Several studies have recorded Alexandrium tamarense in multiple locations around the world, with higher populations favouring temperate waters. This species is not restricted to any specific ocean basin or sea region. In North America, it has been documented in several Canadian and American waters, including the Strait of Georgia (British Columbia, Canada), the Gulf of St. Lawrence (Quebec, Canada), and the Gulf of Maine (Maine, USA). Outside North America, strains have also been recorded in coastal Japan, with recurrent algal blooms in Hiroshima Bay (Japan). Populations have also been found off the coast of Europe, and within the Southern Hemisphere, with populations existing off the coast of Argentina, New Zealand, and Australia. Environmental Conditions Salinity Alexandrium tamarense concentrations have been found in temperate brackish waters around coastal environments. The dinoflagellate has been linked to thriving in regions with freshwater input, increased stratification, and increased nutrients. Research done within the St. Lawrence estuary suggests that there is a strong correlation between low salinity, high freshwater input, and strong bloom development. Temperature Temperature has additionally been found to be a control for Alexandrium tamarense blooms. Peak A. tamarense cell concentrations were found in warmer waters > 12°C. Periods of high precipitation on a day-to-day scale was correlated to high A. tamarense cell counts as well. St. Lawrence Estuary Bloom Dynamics The St. Lawrence estuary in eastern Canada experiences recurrent A. tamarense blooms. This finding led Natsuike et al., 2017 to infer that A. tamarense blooms could occur with future warming, which can have impacts on animal taxa in the Chukchi Sea Shelf. == Saxitoxin ==

Paralytic Shellfish Poisoning Saxitoxin is a potent neurotoxin produced by A. tamarense, marine dinoflagellates, freshwater or brackish water cyanobacteria and is the causative agent of paralytic shellfish poisoning. It is a part of the paralytic shellfish toxins group and has a tricyclic structure with a biguanide group • Tingling • Numbness spreading from lips and mouth to face, neck and extremities • Dizziness • Arm and leg weakness • Paralysis • Headache • Nausea • Vomiting • Respiratory failure and in severe cases death Paralytic shellfish poisoning can occur from eating at risk shellfish, and or contaminated seafood. The saxitoxin profile of A. tamarense (and all Alexandrium spp.) can vary significantly, but is mainly dominated by C2 and GTX4 types. Both the composition and amount of saxitoxin in each cell are variable, with concentrations ranging from 40 to 120 fmol/cell. Impact of nutrients on saxitoxin production Based on the association of saxitoxin production with the nutritional status of A. tamarense, it's thought that nutrient availability plays a significant role in the limitation and amplification of saxitoxin production as well as the growth and development of A. tamarense blooms. A 2015 study demonstrated that for a culture of the A. tamarense strain CI01, collected from the South China Sea, that nitrogen is a much more important nutrient to saxitoxin production than phosphate. However, this causes intracellular toxin levels to accumulate, since the production of saxitoxin is not slowed. This also implies that the maximum concentration of toxin is partially limited by the speed of cell division. == Economic Impact of Harmful Algal Blooms ==

Harmful algal blooms created by A. tamarense can have significant negative economic impacts on the shellfish industry. In the Korean aquaculture industry there has been a loss of US $121 million during the last 3 decades due to harmful algal blooms. In the United States harmful algal blooms have estimated annual costs of $50 million with the following industries spending annually: public health $20 million, commercial fisheries $18 million, $7 million for recreation and tourism impacts, and $2 million for monitoring and management. ==References==