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Asparagopsis armata is a species of marine red algae, in the family Bonnemaisoniaceae.[1] They are multicellular eukaryotic organisms that. This species was first described in 1855 by Harvey,[2] an Irish botanist who found the algae on the Western Australian coast. A. armata usually develop on infralittoral rocky bottoms around the seawater surface to around 40m of depth. Marine algae like A. armata are considered “autogenic ecosystem engineers” as they are at the very bottom of the food chain and control resource availability to other organisms in the ecosystem.[3]

Asparagopsis armata
(Diplodus vulgaris). In the background, Asparagopsis armata
Scientific classification
(unranked):	Archaeplastida
Division:	Rhodophyta
Class:	Florideophyceae
Order:	Bonnemaisoniales
Family:	Bonnemaisoniaceae
Genus:	Asparagopsis
Species:	A. armata
Binomial name
Asparagopsis armata Harvey
Synonyms
Falkenbergia rufolanosa

Population distribution

A. armata is a species native to southern Australia and New Zealand (Southern hemisphere) and is thought to have slowly spread to the Northern hemisphere through the Mediterranean sea, as it is highly invasive. It can now also be found along the British Isles to Senegal as well.[4] The first Mediterranean A. armata was reported in Algeria in 1923. When first found, it seemed strange to find A. armata in this location due to the high summer seawater surface temperatures along southern Mediterranean coasts. However, it was later found that the particular cool water temperatures that stay below 25 °C would allow the species to survive locally during the summer.[2]

Morphology

The fully grown A. armata has sparse branches in which long stolons with harpoon-like hooks and erect shoots develop in all directions. The branches, stolons, and shoots ramify over and over again which give A. armata the thallus-like appearance.[2] The ultimate branchlets are filamentous and composed of three cell rows whereas the larger branches consist of a central medullary filament and a gelatinous matrix surrounded by a cortex 3 – 6 cells thick.[5] Gametophytes are terete and are around 200 mm in height. They form dense, pink intertwining clumps. A characteristic feature of this species is barbs, which attach the A. armata to the ocean benthic substrates.[6]

Life cycle

A. armata have a triphasic diplohaplontic heteromorphic life cycle. In this cycle, the three phases include: haploid carposporophyte, gametophyte and diploid zygote. Multiple phases of different morphology and ploidy contribute differently to the expansion potential of A. armata. Gametophytes of this species are microscopic carposoporophytes and which divide into tetrasporophytes that go through meiosis to be developed into the gametophyte.

A. armata has two morphologically different stages of development– the gametophyte stage and the tetrasporophyte stage.

A. armata goes through haploid and gametophytic phases in a heteromorphic diplo-haplontic life cycle.[2] The A. armata gametophyte grows into adult form and goes through fecundation to produce diploid carposporophyte; which, then, divide into tetrasporophyte that goes through meiosis to be developed into the gametophyte.[7]

Impact of A. armata as an Invasive Species

The acceleration of marine biological invasions through increasing trade and travel also caused the transportation of A. armata to areas outside of their native range: Southern hemisphere. Once it is established, A. armata could rapidly spread and dominate the invaded environment without the direct intervention of human activity.[8] A. armata releases large amounts of toxic compounds to gain competitive advantage in the surrounding invaded area.[9] The impairment of invertebrates after exposure to this algal exudate is shown by significantly increased lipid  (and other biochemical biomarkers) content in the organisms such as common prawn and marine snail.[9] The critical impact that the exudate of A. armata causes, via secondary metabolites, severely decreases the survival rate of various species in the rock pool native communities.[9]

Halogenated metabolites

As a defense mechanism against its predators, A. armata produce halogenated metabolites that chase away herbivores and prevent biofouling. These halogenated metabolites are stored as a refractile inclusion inside specialized gland cells, and are activated with Bromine.

Gland cells of A. armata can take up to 10% of the algal volume, which is a large portion of the plant. Gland cell walls are thin in order to help the transfer of metabolites to the structures that connect the gland cells to the pericentral cells. These structures are stalk-like and allow the metabolite to move to the algae's surface. [10]

References

• Ní Chualáin, F.; Maggs, C.A.; Saunders, G.W. & Guiry, M.D. (2004). "The invasive genus Asparagopsis (Bonnemaisoniaceae, Rhodophyta): molecular systematics, morphology, and ecophysiology of Falkenbergia isolates". Journal of Phycology. 40 (6): 1112–1126. doi:10.1111/j.1529-8817.2004.03135.x. S2CID 53065361.

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