Rhodophyta, Red Algae
Porphyra leucosticta Thuret
Rhodophyta, Order: Bangiales; Family: Bangiaceae.
Porphyra means ‘purplish’ or ‘crimson’ colour, however, the species found in the Eastern Mediterranean tends more towards brown. The alga is better known around the world by its Japanese name - Nori. Leuco means ‘white’ and stica 'dotted’.
The Porphyra leucosticta has a thin, flattened thallus that is sometimes transparent. Often, its edges are rolled. The thallus is single-layered, but quite often several thalli are found growing one upon the other. The thallus is wrapped with a cuticle, a smooth, flexible layer of outer mucous, Through a microscope, it is evident that most of the thallus is comprised of a single layer of cells; however, it is also divided into three segments: the vegetative growing area, the holdfast area, which is comprised of a single layer of cells and, like the vegetative area, contains cylindrical cells; and the reproductive area, which contains reproductive cells and is primarily made up of female cells and a few male cells. This area changes with age.
The species reach a length of about 10 cm, and very rarely 20-30 cm. In aquaculture pools, the Porphyra leucosticta grows as large as 50 cm.
In the wild, the Porphyra leucosticta comes in shades of reddish-brown tending towards a translucent dark brown. When several layers of alga have dried in a heap, the reigning colour is dark brown to black.
The Porphyra leucosticta is characterized by its thin membranous form and its vertical placement - high above the intertidal zone.
In the Eastern Mediterranean the Porphyra leucosticta grows along rocky shores above the intertidal zone, where the waves break. Sometimes, epiphytic individuals can be found upon snails, such as Patella caerulea and Monodonta turbinata.
Biology and reproduction
Being a marine creature, the Porphyra’s ability to withstand dehydration and salinity is amazing. This alga can return to full photosynthetic activity after losing 95% of the liquid in its thallus. More on the Porphyra leucosticta’s life cycle is to be found in the introduction.
Seasonality and distribution
The Porphyra leucosticta can be seen along the shore in the winter; it disappears towards summer, at which point it hibernates in the shells of sea snails. The Porphyra species can be found in nearly all the seas of the world, including northern oceans, temperate sea shores, the Mediterranean and along coasts in Africa and the Far East. It seems that Porphyra leucosticta is an endemic species to the Eastern Mediterranean coast.
The Porphyra leucosticta that grows in this region was researched by Shlomit Kats for her doctoral thesis. This paper supplies, among other things - wide ranges of data regarding the life cycle and breeding habits of the local species. Apparently, as opposed to previously held information, the species common to Israel is not the Porphyra linearis Greville. According to literature, the reproductive spores of the Porphyra linearis are arranged in rows of four, one above the other along the thallus. All are haploid and sexual reproduction does not occur.
According to Kats’s work, our species displays areas containing reproductive male and female cells on the same thallus. One large gamete is located along the length of the female thallus, and two gametes are located in the male thallus, one above the other. On no occasion did she observe four gametes, as described for Porphyra linearis. It is possible, therefore, that there is in this region a local species, or else developed several species that have not yet been classified. Additional species reported in this region are: Porphyra linearis Greville Porphyra umbilicalis (Linn.) J. Agardh.
The Porphyra is one of the most important edible algae in the world. It is especially popular in the Far East Japan, the Philippines and Hawaii - where hundreds of thousands of tones are cultivated and dried annually. The Porphyra is rich in protein (25% - 30% of its dried weight) and minerals. It is a major ingredient in sushi, the famous Japanese dish. In the west, we have evidence, from the beginning of the twentieth century and before, of factories and workshops for processing Porphyra. The Porphyra plant possesses therapeutic and health- related qualities. The alga contains vitamins B and C, and sailors used to eat it to prevent Beriberi disease. In Japan, the alga is also used as a cure against fatty vesicles and a salve for treating wounds.