Phaeophyta, Brown Algae
Dictyota fasciola (Roth) Lamouroux
Phaeophyta, Order: Dictyotales; Family: Dictyotaceae. Formerly, the Dictyota fasciola was included in an additional genus in this family, Dilophus. The two genera, which were barely distinguishable, are currently combined in a single genus: Dictyota.
Dictyota, is derived from the Greek word “diktyon”, meaning ‘a net’. The name of the species means ‘small ribbon’, describing the flat thallus. Fasciola refers to the structure of the thallus, which resembles a cluster of ribbons emanating from the ground.
The Dictyota fasciola is a flat alga that resembles other species of Dictyota. The edges of the thallus are rounded, and the alga stands erect in the water. The thallus structure can be examined through a microscope: small dots can be seen that are, in fact, dark hairs or reproductive cells. The thallus is comprised of three layers, the outer layers having small cells rich in chloroform, and the middle layer, the medulla, made of larger, colourless cells. On part of the central section, two rows of large cells can be seen.
The length of the Dictyota fasciola’s thallus does not usually exceed 10 cm. Its width is about 0.5 cm.
The alga is brown, tending towards olive-green. Dots can be seen inside the thallus. When immersed in water, the alga often takes on a phosphorescent olive-green colour.
The distinction between the Dictyota and Dilophus genera is a thing of the past. The differences between the two were minor: the Dictyota’s medulla is made of a single layer of cells, and that of the Dilophus is made of several layers. Sometimes the edges of the Dilophus seem wider and lighter, spoon-like, as if the erect thallus emanates from a set of rounded shoots. This field finding does not always coincide with laboratory findings, and thus the two genera were combined.
Dictyota fasciola plants grow in shallow water and also in depths of up to 5-8 m. upon a variety of substrates. The species is especially common in tidal potholes.
Biology and reproduction
The sexual and asexual generations of the Dictyota are very similar. The sporophyte (a sexual generation) is diploid and contains reproductive spores. In most common species of Dictyota, the asexual plants are abundant, while sexual generation can rarely be found. One explanation for this phenomenon is that some sporophytic plants do not undergo meiosis, and the resulting diploid spores germinate directly into a new sexual generation. The Dictyota’s manner of branching is a result of the division of vertex cells.
Seasonality and distribution
The Dictyota fasciola begins to appear at the beginning of winter and is quite common during winter and spring. It disappears towards summer and autumn. It can be found in warm seas.
Additional species of Dictyota reported in this region, and which also belong now to this genus, include: Dilophus mediterraneus Schiffner, and Dilophus spiralis )Montagne) Hamel.
Research at the Israeli Oceanographic and Limnological Research Institute by Friedlander and Ben-Amotz revealed vegetative, hormonal-like substances )cytokynins) in the Dictyota fasciola’s thallus. These substances can catalyze plant germination. The research proved that there should be no difficulty in cultivating the Dictyota commercially.