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Rhodophyta, Red Algae

Gelidiella pannosa Feldmann & Hamel

Rhodophyta, Order: Gelidiales; Family: Gelidiaceae.


Gelidus means ‘ice-like’, referring to gelatin, which can be manufactured from the thallus of several Gelidiella species.


The Gelidiella pannosa is an alga made of dense filaments. Its holdfast is very strong, and a knife is needed in order to prise it off a rock to prevent its shredding. The branches are usually erect, and rarely branched. A microscopic cross section reveals that the outer layer (the cortex) incorporates two rows of round cells. The rhizoids are unicellular.


One filamentous thallus is thin, about 1 mm in width. The alga does not usually grow more than 1 cm long.


The alga is dark brown, nearly black, especially when dry.

Special features

The Gelidiella pannosa has a unique habitat on the escarpment. It is able to grow where only a few species of seaweed manage to develop: high above the water line, withstanding extended exposure to the air and almost total dehydration. It is therefore rarely found in the company of other macroalgae.


The Gelidiella pannosa develops on a precipice, at the point where the rock rises above the abrasion platform, on its inner side that is furthest from the sea upon a substrate. The Gelidiella pannosa is usually found on the shaded side of the rock, usually within a notch, but at a considerable height above the platform. Some individuals grow to a height of a metre and more above the intertidal zone (!). The Gelidiella pannosa is mostly exposed to air, dampened only by strong waves.

Biology and reproduction

The Gelidiella pannosa apparently has a three-stage life cycle. The spores are located at the edge of the branches. The branch edges contain one apical cell. A branch that is damaged, from grazing for example, develops a new growth cell and continues growing. The new growth is usually thinner.

Seasonality and distribution

The Gelidiella pannosa are found along the coast throughout the year. There appears to be a certain increase in the community during the winter, perhaps due to a rise in humidity and wave-strength. Gelidiella are found in Australia, the Far East, the Atlantic coastline, Brazil and the Mediterranean.

Additional species

A taxonomy of species in this region is lacking, and additional research will surely add to the scant information existing. Some listed species may be found at the Hebrew University’s herbarium in Jerusalem, and some species are listed in literature, including:

Gelidiella ramelosum Ardis, which is currently referred to as Gelidiella ramellosa (K.tzing) J. Feldmann and Hamel. Nemlich and Danin mention the species Gelidiella lubrica (K.tzing) Feldmann & Hamel.And in Egypt, the species Gelidiella pannosa (Bornet) J. Feldmann and Hamel is mentioned, which is probably the same species as Gelidiella tenuissima (Thuret) J. Feldmann and Hamel.

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