Phaeophyta, Brown Algae

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Sphacelaria Lyngbye, 1819

Phaeophyta,  Order: Sphacelariales; Family: Sphacelariaceae.

Etymology

The generic name refers to its gangrenous appearance, sometimes one of necrosis - a result of its appearance as a mucuosy cover on the rock’s surface.

Description

The Sphacelaria is not immediately evident to the eye, but it is of great importance regarding the coverage and the ecology of the intertidal zone. The alga is made of thin filaments that sometimes branch out. The lower branches of the thallus intertwine with the rhizoids, and the central filaments end in a large apical cell. The sporangia, a distinguishing feature of the species, are multi-cellular and triangular shaped (see illustration).

Size

The Sphacelaria’s thallus can reach a length of 2 cm, but it does not usually grow beyond 1 cm. Its width is a tenth of a millimetre.

Colour

The colour of the Sphacelaria ranges between brown and olive-green, sometimes with a hint of gray.

Special features

The Sphacelaria resemble gray filaments. To identify the genus and species conclusively, a microscope is required. The triangular sporangia characterize the species.

Habitat

The Sphacelaria covers wide areas of rocks in the intertidal and subtidal zones. Often, it is an epiphyte on other algae or creatures.

Biology and reproduction

The Sphacelaria undergoes both sexual and asexual reproduction; asexual reproduction is more common than sexual. The life cycle is controlled by environmental conditions: temperature and daylight hours.

Many fish feed on Sphacelaria and, after the polysiphonia, it is their most favoured algae for grazing.

Seasonality and distribution

The Sphacelaria tribuloides can be found throughout the year. The species is widely distributed in temperate and tropical seas.

Additional species

Four species of Sphacelaria have been described in the Eastern Mediterranean, and there may be more. Among them, the Sphacelaria tribuloides Meneghini, which covers extensive areas in tidal pools in the intertidal zone; the Sphacelaria cirrosa (Roth) C. Agardh = Sphacelaria pennata Lyngbye has sporangia comprised of four horns which emanate from a central point (see illustration); Sphacelaria rigidula  Kutzing  and Sphacelaria furcigera  Kutzing , which has trichotomous sporangia that emanate from a central point (see illustration). In some publications Sphacelaria rigidula and Sphacelaria furcigera are described as synonyms. Without doubt, this genus’ distribution in the Eastern Mediterranean basin requires further investigation.

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