The brown algae, comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds. Between 1,500 and 2,000 species of brown algae are known worldwide. Most brown algae contain the pigment fucoxanthin, which is responsible for the distinctive greenish-brown color that gives them their name. Regardless of size or form, two visible features set them apart from all other algae:
1. Members of the group possess a characteristic color that ranges from an olive green to various shades of brown. The particular shade depends upon the amount of fucoxanthin present in the alga.
2. All brown algae are multicellular. There are no known species that exist as single cells or as colonies of cells, and the brown algae are the only major group of seaweeds that does not include such forms.
Most brown algae live in marine ecosystems, where they play an important role both as a food and as habitat. They have adapted to a wide variety of marine ecological niches including the tidal splash zone, rock pools, the whole intertidal zone and relatively deep near shore waters. A large number of them are intertidal or upper littoral, and they are predominantly cool and cold-water organisms that benefit from nutrients in up welling cold-water currents and inflows from land. They are an important constituent of some brackish water ecosystems and have colonized freshwater on a maximum of six known occasions. In addition, they also have environmental significance through carbon fixation.
We present you our small guide with 13 species that we have founded in Ieranto bay that are an important part of life communities in this marine ecosystem
Padina pavonica (Peacock tail)
Description: Thallus is fixed by a tuft of rhizoids with a short, cylindrical base forming a conical pedicel. Grows up to 15 cm high is a zoned fan blade, ciliate margin, white and brown, encrusted with limestone, with a short peduncle. The surface of the thallus is decorated with fine concentric rows of hair. The growth of the thallus is by margins. Many individuals are often grouped as born from the same basal system crawling.
Ecology: Colonizes the well-lit hard substrates of the sub-littoral stage, in calm or little agitated water. It is observed from the surface up to 20 meters or more in the eastern Mediterranean. Cosmopolitan.
Fun fact: Scientific research has shown that Padina pavonica has properties reminiscent of those of young human skin!
Zonaria tournefortii (Yellow zoned)
Description: This leafy alga has dichotomous lobes, with concentric striations . On the margin of the thallus is a row of initial marginal cells ensuring apical growth. A reddish midrib is visible at the base of the thallus , but fades rapidly. The thallus, yellowish brown, can reach 20 cm. The whitish color on the upper part corresponds to a deposit of calcium carbonate in the form of aragonite.
Ecology: Inhabitat infralitoral less illuminated places. Present in the Mediterranean up to 20 m depth (except in the Gulf of Lion and the Adriatic), in the East Atlantic, in the Caribbean Sea and in Brazil. Pantropical.
Fun fact: Survivor of Tethys, this seaweed is widespread in many warm seas and oceans without human intervention.
Dictyota dichotoma (Fork weed)
Description: Thalle flattened into strips. Branching is dichotomous. The branches are of the same length, true dichotomy. The top of the branches is rounded. The seaweed attaches to the substrate by rhizoids which end in adhesive discs. Color varies from brown to green and is characterized by a blue iridescence during its vegetative growth phase, visible only under water. Can reach up 10 to 25 cm long.
Ecology: Very common on rocks and species of the genus Cystoseira, in quiet places near the surface and often associated with other species. Rare at great depths. It lives attached to hard substrates, in rocky, sandy or muddy bottoms, up to 20-25 meters deep. Present in Mediteran sea, Atlantic Ocean and the Red sea.
Fun fact: The species can tolerate a certain rate of organic pollution!
Dictyota fasciola (False forked ribbons)
Description: Thallus erect in the form of narrow ribbons up to 20 cm high and 1 to 2 mm wide. The thallus is membranous, light brown to greenish in color, with narrowed and tapered (acute) ends often curved . The straps are devoid of midrib. Branching is pseudodichotome in a plane. The dichotomies are few in number, and form an acute angle. Apical growth. The straps are highly spiral. Both sides of the thallus bear groups of isolated hairs. Thallus is attached to the substrate by stolons.
Ecology: Visible on rocky substratum from spring to autumn, up to 10m deep in well illuminated environments. Distribution in Mediterranean and temperate eastern Atlantic (Channel to Cape Verde, Azores, Canary Islands).
Fun fact: From Greek [dictyota] = net-shaped and fasciola : from Latin [fasciolum] = small ribbon.
Description: Thallus flat and leaf-like, to 300 mm long (usually 100-150 mm) and 10-40 mm broad; fronds thin and translucent, olive to yellow-brown, irregularly formed-laminate, lacking a midrib; reproductive structures characteristically formed in wavy bands.
Ecology: Habitat are sunny, sandy pools in the lower intertidal in summer. Relatively rare. Widely distributed but only locally common in western Ireland and south-western Britain, south to Senegal; widespread in the Mediterranean sea.
Fun fact: It is distinguished from genus Dictyota by the irregular, never dichotomous branching of the thallus.
Cystoseira compressa (Flattened Cystoseira)
Description: Upright, tree-like algae that is greenish yellow to dark brown in color. Height reach from a few cm in a beaten habitat to more than 50 cm and up to 1 m in calm environment (small ports). Fixed on the rock by a small discoid base from which there are several axes measuring 2 to 3 cm. The thallus is smooth, devoid of spiny ramules. Young alga, form characteristic rosettes, with their flat and short branches arranged horizontally on the substrate.
Ecology: Attached to hard substrates of the infralittoral, near the surface, between 0 and 2 m deep, but sometimes deeper (up to 40 m). Present in semi-beaten mode as well as in quiet mode. Mediteran and North East Atlantic.
Fun fact: Among the Cystoseires, it is the species most resistant to pollution, which explains its presence in some moderately polluted harbor areas.
Cystoseira compressa var. pustulata (Cystoseira)
Description: Also upright, tree-like algae that has characteristic beige, light green in color. Fixated with discoidal base from which are starting few straight holdfasts that can reach up to 25 cm, cylindrical and short, that are holding branching rames. Small aerocysts are also present. Apical growth from one cell that can not be seen without a microscope.
Ecology: Typical for the marine pools and well illuminated places of infralitoral down to 15m in depth. It can also grow as epiphytes of other Cystoseira and rhizomes of Cymodocea nodosa. Present in Mediterranean sea.
Fun fact: Easily distinguished from other C. compressa by its very light beige color, its primary branches barely compressed at the base and its crypts piliferous large and prominent (pustular appearance).
Cystoseira mediterranea (Valiante grass)
Description: Straight tree-like algha, greenish to brown in color up to 40 cm high attached to the bottom with discoidal base from which are growing cylindric holdfasts up to 15 cm with branching rames. Primary branches very long up to 30 cm high. In some thalluses aerocysts could be founded. Apical growth.
Ecology: Present on rocky substrate subject to rising currents from 0 to 1.5 m. The species tolerates restricted variations in temperature and salinity. Indicates the presence of cold water due to rising phenomena or widespread infiltration of groundwater. In Italy it is present in the Gulf of Naples, on the eastern coast of Sicily and in Pantelleria.
Fun fact: Mediterranean endemic species! Threatened mainly by urban, industrial, agricultural and livestock pollution.
Dictyopteris polypodioides (Sea fern)
Description: The thallus is long, flattened (banded), of greenish brown color, more or less translucent, with pseudodichotomous divisions. It can reach 30 cm in length and 3 to 20 cm wingspan. It branches into strips 2 to 10 mm wide, formed of a central rib, very visible from the base to the ends, bordered on both sides by a membranous polystromatic margin. At its base, just above the fixation disc, the thallus is often reduced to the thickened central vein. The consistency is membranous and fragile.
Ecology: This alga is present on rocky bottoms from the surface up to 40 m deep. In the Atlantic, it is found under the fronds of kelp. It can also be found in photophilic biotopes in the southern Mediterranean.
Fun fact: This seaweed is harvested by hand. It is used as food. Its antibiotic action is demonstrated and it is also a popular medicine in the Mediterranean countries (treatment of respiratory diseases, scrofula).
Dictyopteris lucida (Mediterean sea fern)
Description: The thallus is long, banded, of greenish brown color, more or less translucent, with pseudodichotomous divisions. Reaches up to 30 cm in length and 3 to 20 cm wingspan. Algae is attached to the substrate by a thick basal disk. It branches into strips (or strips) 2 to 10 mm wide, formed of a central rib, very visible from the base to the ends, bordered on both sides by a membranous polystromatic margin. Consistency is membranous and fragile. Ecology: From the summer, this alga changes appearance, with slender fronds around their central veins. Present on rocky bottoms from the surface up to 40 m deep. In the Atlantic, it is found under the fronds of kelp. Cosmopolitan.
Fun fact: This seaweed releases a strong odor when it is out of the water.
Halopteris scoparia (Sea broom)
Description: Alga forms compact tufts of filaments 5 to 15 cm high , voluminous and coarse. The set looks like a little broom of branches (broom) dark brown color. The species is polymorphic (different forms described). The main axes are clear and branched in all directions. The broom, which is bushy in summer, usually has a more regular shape in winter. Ecology: Inhabitat rocky and sandy bottoms. It is found all year round from the surface until about 15 m deep. Found throughout the whole year in abundance from the mid-tide zone and in the upper infralittoral zone. Present in the Mediterranean sea. and East and West Atlantic. Fun fact: This seaweed has antibacterial properties. It is also rich in growth substances (phyto-hormones) that are used in cosmetics in “anti-aging” creams.
Description: Frond narrow, tough and wiry, but soft to the touch, dark brown to black when dry, 2-3 mm wide and up to 25 cm long. Strongly resembling a bottle-brush plant or laboratory glass-cleaning brushes because of whorls of filaments arising from the main axis (below, magnified). Branching irregularly dichotomous. Apical growth. The coralline alga Jania rubens is frequently found growing as an epiphyte at the base of the fronds.
Ecology: On rocks and stones, generally in areas affected by sand, intertidal and shallow subtidal. Widely distributed and common. Present in the Mediterranean sea.
Fun fact: New resurges shows that this alga has a high concentration of polyunsaturated fatty acids (PUFA) which our body can not sintetise. Therefore, it could be a new source of this important element in our diet.
Colpomenia sinuosa (Ballweed)
Description: Fixed to the substrate by filamentous rhizoids, this alga of brittle consistency reaches the size of 8 cm. It presents itself as an irregular hollow ball and split greenish yellow, covered with small tufts of fine hair. The sori punctiforms are arranged around tufts of hair. Sori are small bag containing spores. At first the thallus is globular, solid and without tuft of hair, then it takes a cerebral form.
Ecology: Founded in shallow and well-lit bottom from the surface up to 10 m, on rocks and other algae. It tolerates water loaded with organic matter, which is poorly oxygenated and rich in sulfur and nitrogen compounds. Its development is maximum in spring and summer, this brown alga is nonetheless present all year round. Fun fact: It tolerates large variations in temperature and salinity.
The brown algae include the largest and fastest growing of seaweed. Fronds of Macrocystis (giant kelp) may grow as much as 50 cm (20 in) per day, and the stipes can grow 6 cm (2.4 in) in a single day!
Brown algae also include a number of edible seaweeds, that are used by many nations through centuries. Some species have become subjects of extensive research in their own right due to their commercial importance.
All brown algae contain alginic acid (alginate) in their cell walls, which is extracted commercially and used as an industrial thickening agent in food and for other uses. This polysaccharide is a major component of brown algae, and is not found in land plants. One of these products is used in Lithium-ion batteries. Alginic acid is used as a stable component of a battery anode. Fascinating right?
Full of potential, biological and industrial, they are providing protection and food to enormous groups of organisms, therefore, they need to be protected and understood. Just one of the shades of many colors of the sea. Be sure to check our other 2 guides for red and green algae to have full picture of Ieranto bays colors.
This algae study was made by the Project M.A.R.E volunteers of 2019.