Blue Ecosystems יעוץ סביבתי, בהנהלת ד"ר רחלי עינב - Asparagopsis taxiformis

 

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דף הבית >> Seaweeds of Eastern Mediterranean coast >> Rhodophyta >> Asparagopsis taxiformis
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Rhodophyta | Chlorophyta | Rhodophyta
Asparagopsis taxiformis (Delile) Trevisan






Taxonomy
Rhodophyta, Order: Bonnemaisoniales; Family: Bonnemaisoniaceae.
Etymology
Asparagopsis refers to its resemblance to the asparagus  plant. The name of the species -taxiformis -refers to the  arrangement of its branches, which resembles that of the  Yew tree.
Description
The Asparagopsis taxiformis is a very soft alga that loses  its shape when extracted from the water. The central axis is  covered with irregular lateral fissures 1 cm in diameter at the  base and several millimetres at the tip. The fissures are  arranged in a pyramid form - sharpened at the end. The algal  cling is made of several crawling shoots that attach to a  substrate using a wedge-like rhizoid, often forming a thicket  at the base of the colony. Microscopic examination reveals  2 rows of cells along the side branches.
Size
The Asparagopsis taxiformis is between 5 to 20 cm long  (very rarely - 30 cm), but most are in the 10 cm region. The  side branches (the algal diameter) varies between several  millimeters to a centimeter (a 2 cm diameter is rare).
Colour
The Asparagopsis taxiformis comes in shades of pink,  veering towards gray or very light brown. Usually, the algal  base is pinker and its top grayish.
Special features
The Asparagopsis taxiformis is found in dense colonies,  coloured pinkish-brown, and characterized by its soft thallus  and pyramid shape. It may be confused with Dasya plants,  but that plant’s characteristic pompoms are missing, and it  is very rare.

Habitat
Rocky beaches of the Eastern Mediterranean are where the  Asparagopsis taxiformis grows attached to the substrate,  creating dense colonies in the upper region of the subtidal  zone, in areas that are never exposed. In literature, the  Asparagopsis taxiformis has been reported at depths of 15  to 30 m. In Australia and other places, the alga is considered  an epiphyte, and it apparently also grows on ships, which  transport it from one place to another.
Biology and reproduction
The Asparagopsis taxiformis three staged life cycle includes  a gametophytic stage (described below) and a sporophytic  stage. The algal gametophyte holds in the base of its  branches round, but sometimes elongated, sporangia whose  diameter may be 1 mm, but they are usually smaller. The  sporophytic branches resemble a bundle of hairs, have  elongated sporangium bodies, are usually located in the  top of central branches and resemble the branches of the  Polysiphonia alga. Microscopic examination from above  reveals filaments containing 2 rows of cells, sharpened at  the edges and irregularly branched. The holdfast is disk- like. The sporophytic branches grow to 2 cm in length and  are pinkish-red coloured. Not all stages of the life cycle  have been observed in all those places where the alga has  been reported, and the sporophytic stage may also be able  to reproduce by fragmentation.
Seasonality and distribution
The Asparagopsis taxiformis is rare in this region. I myself  have only seen it twice along Israeli shores: in Mikhmoret,  where it was also reported by Dr. Lundberg, and at the Neve  Yam beach (Israel). The species has also been reported in  Egypt by its previous name -Asparagopsis delilei  Montagne. The algal tropical and sub-tropical distribution  is wide, arriving in Europe at the beginning of the twentieth  century, probably by ship.
Additional species
The Asparagopsis genus includes two species, but only  one of them, the Asparagopsis taxiformis, has so far been  reported in our region. The other species is only known to  exist in Australia and New Zealand.
The algal sporophytic stage was erroneously considered a  separate species - the Polysiphonia hillebrandii Bornet until  1961, and as the Falkenbergia hillebrandii (Bornet)  Falkenberg thereafter.
Asparagopsis taxiformis, on the right:  procarp, on the left: cistocarp - an  asexual structure developed as a  parasite in the female sporophyte.
 Asparagopsis taxiformis -a general view of the cellular  arrangement at the edge of the holdfast, from which several  rhizoids branch out.
 
In the Caribbean Islands, the Asparagopsis taxiformis is a popular consumable, used as a spice and a common addition  to fish and meat dishes.

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