Heterosigma akashiwo

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Heterosigma akashiwo
CCMP452.jpg
Scientific classification
(unranked):
SAR
Superphylum:
Heterokonta
Phylum:
Ochrophyta
Class:
Raphidophyceae
Order:
Chattonellales
Family:
Chattonellaceae
Genus:
Heterosigma
Species:
H. akashiwo
Binomial name
Heterosigma akashiwo
(Y. Hada) Y. Hada ex Y. Hara & M. Chihara

Heterosigma akashiwo is a species of microscopic algae of the class Raphidophyceae. [1] [2] It is a swimming marine alga that episodically forms toxic surface aggregations known as harmful algal bloom. The species name akashiwo is from the Japanese for "red tide". [1]

Contents

Synonyms include Olisthodiscus luteus (Hulburt 1965), and Entomosigma akashiwo (Hada 1967). [3] H. akashiwo and H. inlandica have been recognized as two species of Heterosigma. However, Hara and Chihara (1987) described both specimens as one species, validly describing them as H. akashiwo. [4]

Description

H. akashiwo cells are relatively small, ranging in size from 18 to 34 μm in diameter. [5] They appear golden brown, and appear in clusters. Morphology is highly variable, but does not appear to vary significantly between locations. One culture may contain flat or round individual cells. [5] Molecular techniques for identification (including quantitative PCR) are preferred over traditional microscope fixing, which may lyse the cells. [5]

Heterosigma akashiwo anatomy from Hara and Chihara 1987 Hara and Chihara Fig 21.jpg
Heterosigma akashiwo anatomy from Hara and Chihara 1987

Distribution

Heterosigma akashiwo has been identified off the coasts of the United States, Canada, Chile, the Netherlands, Scotland, Ireland, Sweden, Norway, Japan, S.Korea, Hong Kong, Australia, New Zealand and South Africa. [1] [6] [7] [8] Most of the literature suggests H. akashiwo is associated with shallow water within 10 m of the surface, but this is not a universal rule. [7]

Physiology

Heterosigma akashiwo is a mixotrophic alga, supplementing nutrient uptake and photosynthesis with ingestion of bacteria. [9] Each cell may contain 18-27 chloroplasts. [5] These cells have been observed to glide and twirl under microscopic examination, but nonmotile cells have been associated with toxic blooms. [5] [7] Blooms are clearly visible by air, appearing as a red area in otherwise blue water. [7] Optimal growth occurs at 25 °C and 100 μE m−2s−1, conditions which are associated with very low toxicity. [10] Maximum toxicity occurs (and relatively slow growth) occurs at 20 °C and 200 μE m−2s−1. [10] H. akashiwo reproduces asexually by binary fission. [4]

Heterosigma akashiwo produces cysts as a resting stage. [2] [11] The germination of these cysts leads to large-scale blooms, which can be laterally transferred by tides and currents. [7] A 2007 review of these blooms in Puget Sound suggested that salmon farming was probably not a strong driver of their incidence or severity. [7] Bottom water temperature must reach at least 15 °C for germination to occur. Blooms are most often associated with summer months, and some areas may see two blooms within one year. [7] Blooms are known to be lethal once concentrations of cells reach 3x105 to 7 x 105 cells/L. [7] Viruses may act as a natural control on bloom populations, as H. akashiwo viruses (HaV) have been shown to only leave resistant alga alive. [12] Similarly, certain bacteria may also reduce H. akashiwo populations. [13]

The exact mode of bloom toxicity is currently unknown, but gill damage leading to hypoxia is the proposed cause for fish death. [5] [7] H. akashiwo may produce brevetoxins, but others suggest the concentrations of these toxins are too low to account for such a large effect on fish populations. [7] [14] Some have argued the production of reactive oxygen species like hydrogen peroxide may be responsible for gill damage. However, research suggests hydrogen peroxide concentrations are far too low to have significant effects on fish. [15] Mucus production is another proposed, but poorly supported, mechanism for fish mortality. [7] The effective toxin possibly is chemically unstable, and therefore difficult to detect. [7] Sablefish appear to be unaffected by H. akashiwo blooms, while many other marine fish are decimated. [7]

Genetics

Genetic sequences are highly conserved between Pacific and Atlantic populations. Relevant probe sequences for small subunit RNA can be found. [5]

Economic impact

Heterosigma forms massive golden tides that impact the survival of organisms at every trophic level. This alga has been shown to kill finfish, compromise fish and sea urchin egg development, and impact copepods, as well as oyster survival. [16] Further ecological impacts to plankton, invertebrates, and wild fish are likely, but unknown. [7] The 1997 H. akashiwo bloom in British Columbia, for example, coincided with a dramatic increase in mortality of captive salmon. [17] H. akashiwo contributed to the loss of over 1,000 tons of Atlantic salmon in 2001. [6] A bloom in Puget Sound in 2006 led to the loss of $2 million of farmed salmon. [7] In 2014, a bloom near Port Hardy, British Columbia, killed nearly 280,000 Atlantic salmon. [18] In 2018, a bloom near British Columbia killed near 250,000 Atlantic salmon at two seafood farms. [19] In March 2022, a H. akashiwo bloom, triggered by sewage pollution, in the Swartkops River estuary in Port Elizabeth, South Africa, killed thousands of fish and crustaceans, compromising the ecosystem value of the estuary as a "fish nursery" that benefits ecosystem diversity and the fishing industry. [8] 1995 article noted that the global distribution of H. akashiwo is increasing, as is the frequency of H. akashiwo HAB formation. [20]

Related Research Articles

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An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term algae encompasses many types of aquatic photosynthetic organisms, both macroscopic multicellular organisms like seaweed and microscopic unicellular organisms like cyanobacteria. Algal bloom commonly refers to the rapid growth of microscopic unicellular algae, not macroscopic algae. An example of a macroscopic algal bloom is a kelp forest.

Prymnesium parvum is a species of haptophyte. The species is of concern because of its ability to produce the phycotoxin prymnesin. It is a flagellated alga that is normally found suspended in the water column. It was first identified in North America in 1985, but it is not known if it was introduced artificially or missed in previous surveys. Toxin production mainly kills fish and appears to have little effect on cattle or humans. This distinguishes it from a red tide, which is an algal bloom whose toxins lead to harmful effects in people. Although no harmful effects are known, it is recommended not to consume dead or dying fish exposed to a P. parvum bloom.

Phycodnaviridae is a family of large (100–560 kb) double-stranded DNA viruses that infect marine or freshwater eukaryotic algae. Viruses within this family have a similar morphology, with an icosahedral capsid. As of 2014, there were 33 species in this family, divided among 6 genera. This family belongs to a super-group of large viruses known as nucleocytoplasmic large DNA viruses. Evidence was published in 2014 suggesting that specific strains of Phycodnaviridae might infect humans rather than just algal species, as was previously believed. Most genera under this family enter the host cell by cell receptor endocytosis and replicate in the nucleus. Phycodnaviridae play important ecological roles by regulating the growth and productivity of their algal hosts. Algal species such Heterosigma akashiwo and the genus Chrysochromulina can form dense blooms which can be damaging to fisheries, resulting in losses in the aquaculture industry. Heterosigma akashiwo virus (HaV) has been suggested for use as a microbial agent to prevent the recurrence of toxic red tides produced by this algal species. Phycodnaviridae cause death and lysis of freshwater and marine algal species, liberating organic carbon, nitrogen and phosphorus into the water, providing nutrients for the microbial loop.

<i>Karenia brevis</i> Species of dinoflagellate

Karenia brevis is a microscopic, single-celled, photosynthetic organism in the genus Karenia. It is a marine dinoflagellate commonly found in the waters of the Gulf of Mexico. It is the organism responsible for the "Florida red tides" that affect the Gulf coasts of Florida and Texas in the U.S., and nearby coasts of Mexico. K. brevis has been known to travel great lengths around the Florida peninsula and as far north as the Carolinas.

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Marnaviridae is a family of positive-stranded RNA viruses in the order Picornavirales that infect various photosynthetic marine protists. Members of the family have non-enveloped, icosahedral capsids. Replication occurs in the cytoplasm and causes lysis of the host cell. The first species of this family that was isolated is Heterosigma akashiwo RNA virus (HaRNAV) in the genus Marnavirus, which infects the toxic bloom-forming Raphidophyte alga, Heterosigma akashiwo. As of 2021, there are twenty species across seven genera in this family, as well as many other related virus sequences discovered through metagenomic sequencing that are currently unclassified.

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References

  1. 1 2 3 Guiry, M. "Algaebase" . Retrieved 3 October 2011.
  2. 1 2 Hallegraeff, G.M.; Hara, Y (2003). Hallegraeff, D.M.; Anderson, D.M.; Cembella (eds.). Manual on Harmful Marine Microalgae. UNESCO Publishing. ISBN   978-92-3-103871-6.
  3. ↑ Throndsen, J (1996). "Note on the taxonomy of Heterosigma akashiwo (Raphidophyceae)". Phycologia. 35 (4): 367. doi:10.2216/i0031-8884-35-4-367.1.
  4. 1 2 3 Hara, Y; M. Chihara (1987). "Morphology, ultrastructure and taxonomy of the raphidophycean alga Heterosigma akashiwo". Journal of Plant Research. 100 (2): 151–163. doi:10.1007/bf02488320. S2CID   10393570.
  5. 1 2 3 4 5 6 7 Bowers, H. A.; Tomas C., Tengs T., Kempton J. W., Lewitus A. J., and D. W. Oldach (2006). "Raphidophyceae [Chadefaud Ex Silva] systematics and rapid identification: sequence analyses and Real-Time PCR Assays". Journal of Phycology. 42 (6): 1333–1348. doi:10.1111/j.1529-8817.2006.00285.x. PMC   2856949 . PMID   20411032.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. 1 2 Lars-Johan, N; Einar D., and D. Didrik (2002). "A new bloom of Chattonella in Norwegian waters". Harmful Algae News. 23: 3–5.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Rensel, J. E. (2007). "Fish Kills from the harmful alga Heterosigma akashiwo in Puget Sound: recent blooms and review". National Oceanographic and Atmospheric Administration Technical Report.
  8. 1 2 Rogers, Guy (29 March 2022). "Sewage pollution surge threatens besieged Swartkops again". The Herald. Retrieved 4 September 2022.
  9. ↑ Smayda, T. J. (1997). "Harmful Algal Blooms: Their ecophysiology and general relevance to phytoplankton blooms in the sea". Limnology and Oceanography. 42 (5): 1137–1153. Bibcode:1997LimOc..42.1137S. doi:10.4319/lo.1997.42.5_part_2.1137. S2CID   16822520.
  10. 1 2 Ono, K; Khan S., and Y. Onoue (2000). "Effects of temperature and light intensity on the growth and toxicity of Heterosigma akashiwo (Raphidophyceae)". Aquaculture Research. 31 (5): 427–433. doi: 10.1046/j.1365-2109.2000.00463.x .
  11. ↑ Kim, J. H.; Park, B. S.; Wang, P.; Kim, J. H.; Youn, S. H.; Han, M. S. (2015). "Cyst morphology and germination in Heterosigma akashiwo (Raphidophyceae)". Phycologia. 54 (5): 435–439. doi:10.2216/15-26.1. S2CID   85790577.
  12. ↑ Tarutani, K; Nagasaki K., and M. Yamaguchi. (2000). "Viral impacts on total abundance and clonal composition of the harmful bloom-forming phytoplankton Heterosigma akashiwo". Applied and Environmental Microbiology. 66 (11): 4916–4920. Bibcode:2000ApEnM..66.4916T. doi:10.1128/AEM.66.11.4916-4920.2000. PMC   92399 . PMID   11055943.
  13. ↑ Ishida, Y; Yoshinaga, I; Imai, I; Nagasaki, K; Itakura, S; Uchida, A; Ishida, Y (1998). "A close relationship between algicidal bacteria and termination of Heterosigma akashiwo (Raphidophyceae) blooms in Hiroshima Bay, Japan". Marine Ecology Progress Series. 170: 25–32. Bibcode:1998MEPS..170...25K. doi: 10.3354/meps170025 .
  14. ↑ Khan, S; Arakawa O., and Y. Onoue. (1997). "Neurotoxins in a toxic red tide of Heterosigma akashiwo (Raphidophyceae) in Kagoshima Bay, Japan". Aquaculture Research. 28: 9–14. doi: 10.1111/j.1365-2109.1997.tb01309.x .
  15. ↑ Twiner, M. J.; Dixon S. J., and C. G. Trick. (2001). "Toxic Effects of Heterosigma akashiwo do not appear to be mediated by hydrogen peroxide" (PDF). Limnology and Oceanography. 46 (6): 1400–1405. Bibcode:2001LimOc..46.1400T. doi: 10.4319/lo.2001.46.6.1400 .
  16. ↑ Keppler, Charles J. (2005). "Sublethal effects of the toxic alga Heterosigma akashiwo on the southeastern oyster (Crassostrea virginica)" (PDF). Harmful Algae. 4 (2): 275–285. doi:10.1016/j.hal.2004.05.002.
  17. ↑ "Archived copy" (PDF). Archived from the original (PDF) on 2006-02-26. Retrieved 2007-03-25.{{cite web}}: CS1 maint: archived copy as title (link)
  18. ↑ "Marine Harvest Canada, Salmon Farming in British Columbia".
  19. ↑ Huffman, Jason (6 June 2018). "Algal bloom kills half of Grieg's salmon at two British Columbia farms". Undercurrent News. Retrieved 2018-06-08.
  20. ↑ Anderson, Donald M. (July 1995). "Toxic red tides and harmful algal blooms: A practical challenge in coastal oceanography". Reviews of Geophysics. 33 (S2): 1189–1200. Bibcode:1995RvGeo..33S1189A. doi:10.1029/95RG00440.
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