Order: Fucales; Family: Cystoseiraceae.

Etymology

Cystoseira means ‘chain of vesicles’, and it describes the air pockets in the thallus.

Description

Cystoseira (as well as sargassum) are the largest algae in the Eastern Mediterranean. The Cystoseira has a developed holdfast that connects it to the substrate, and cylindrical or flattened branches that sometimes contain a central vein. Cystoseira resemble a branched bush. The division of holdfast, stipe (a thickended stemlike structure) and branch containing a central axis and leaf-like branches indicates the algal high level of development, although not as high as that of the Sargassum. Most Cystoseira have air vesicles, which are a part of the stalk-like thallus and not to be found in separate organs, as in Sargassum.

Size

Many Cystoseira plants reach a length of 20 cm; an examination of an entire colony showed larger individuals reaching even 50 cm.

Colour

Cystoseira are shades of light brown and cream. Sometimes the colour is uniform, and sometimes spots are evident. In water, they seem greener than outside, a result of return radiation by chlorophyll-a. Upon dehydration, the thallus gains a darker shade.

Special features

The Cystoseira genus is easy to identify, but it is harder to differentiate the species. For this, it is important to collect whole individuals, with their holdfasts. Near the holdfast, one finds the keys to classification. Identification is based on the shape of the holdfast, the number of stipes emanating from it, the shape of toful (the swelling at the base of the branches) and the perforations in between the branches (see glossary below).

Habitat

Most Cystoseira plants are encountered in the upper regions of the intertidal zone, usually in places that are not exposed to the air during low tide. A small number of species are deep sea algae. Most, algae that develop in the calmer waters of the deep have a single stipe , and those that develop in habitats with stronger currents have several stipes.

Biology and reproduction

The Cystoseira is a most fascinating alga, as well as being both prominent in the field and an important component of the marine community. As a result, it is also the focus of extensive research.

Like other series members, the Cystoseira reproduces sexually exclusively (oogamy), and it has no asexual spores. Along the thallus one finds cavities that usually contain hairs and sometimes also male and/or female reproductive cells. The location of reproductive organs is often an important aide in defining species.

The genus is divided into three groups, distinct from one another in their developmental level from several aspects. The most developed group includes the Cystoseira mediterranea, the Cystoseira brabata and the Cystoseira crinita. These species are distinct from the other species in various aspects, as well as their life cycle: the embryo does not sprout in water or upon the substrate, but within the female plant’s body. Male gametes are coloured red by a pigment from the carotenoid group; the pigment is a primitive eyespot (stigma), which assists in locating the  emale gametes to attach to.

Species belonging to more primitive groups (Cystoseira abrotanifolia, Cystoseira spinosa) contain reproductive cells that develop on branches and are secreted directly into the water. Following fertilization the zygote drifts in the water until it finds a place to settle.

Upon the rocks of California, several fossilized species can be found that belong to the Cystoseira group, and which have become extinct over the period of evolution. Some, however, continue to exist.

Seasonality and distribution

Most Cystoseira species are perennial, although branches shed and change after several months. Extremely old individuals have been found around the world, which continue to live for ten years, and maybe even more. The Cystoseira genus inhabits the Mediterranean. About two thirds of the genus’ forty species are endemic to the Mediterranean or at least to parts of it. Cystoseira plants are relatively large, evolutionarily developed and comprise a significant component of the marine environment, as trees in the forest.

Additional species

Along the intertidal zone of the Israeli coast, three species are apparently common: Cystoseira compressa, Cystoseira rayssiae (endemic) and Cystoseira schiffneri. Species unreported along the Israeli coast have been described in Turkey and Lebanon, in the north, and in Egypt to the south. It may be assumed that they are the same species that exist along the Israeli coast, but there is a need for further research. These include:

Cystoseira corniculata (Wulfen) Zanardini Cystoseira spinosa Sauvageau Cystoseira amentacea (C. Agardh) Bory Cystoseira barbata C. Agardh.

Edelstein reports finding Cystoseira platyramosa Ercegovi. in the Haifa Bay at a depth of up to 80 m. The alga has a small disk holdfast and is cylindrical at the bottom up to about half its length. The thallus then becomes flat and dichotomously branched. The side branches sport main veins along their sides.

In the depths of the Mediterranean, two species are known, both smaller than those in the intertidal zone: Cystoseira fucoides Ercegovic = Cystoseira dubia Valiante and Cystoseira platyramosa Ercegovi.. These species have also been described as having flat branches and a delicate central vein.

Two species described by Carmin in 1934 are:

Cystoseira fibrosa (Hudson) C. Agardh = Cystoseira baccata Gmelin Cystoseira granulata C. Agardh = Cystoseira nodicaulis Withering.

Cystoseira mediterranea Sauvageau has been reported both in Egypt and Turkey. It has not yet been observed in the Eastern Mediterranean, and there is therefore doubt regarding the identification, since the alga is easily confused with Cystoseira amentacea. Both have a similar structure, but the Cystoseira mediterranea has a unique stipe. The Cystoseira amentacea is a deep sea alga and is never exposed to the air.

 Research at the Israel Oceanographic and Limnological Research Ltd. (IOLR) Institute by Friedlander and Ben Amotz revealed vegetarian, hormonal-like materials  (Cytokinine) in the thallus of Cystoseira. These materials can assist the sprouting of plants.

 

 

Key to species of Cystoseira

The following key is based on the work of Professor G. Giaccone from Italy and his students (Amico et al., 1995). It was translated from the Italian and updated with his gracious assistance.

Species of Cystoseira have undergone a lengthy period of marine evolution. The differences are clear, and after acquainting ourselves with the parts of the plant, it is usually possible to identify the species using binoculars, and there is no need for microscopic sections.

For the purpose of identification, it is important to collect the plant in its entirety, since the base of the plant, the holdfast and the lower ‘stalks’ are of consequence to the identification process.

Elements to be identified:

1. Holdfast: one must examine whether it is made of one unit (compact) or divided into several joints.

2.  Stipe: Does a single stipe, even a short one, emanate from the base of the holdfast, or do several, and is it erect or creeping.

3.  Apex: in some species a protrusion appears in between the ‘stipe’, an ‘apex’ that does not develop into a branch. The apexes are identified according to size, shape and presence or absence of thorns and hair. Sometimes the apex is absent.

4.  Toful: condensation at the base of the branches that appears in young or potential branches as well, and contains storage substances that help the development of the branch. The toful appears mostly in species that have only one stipe. The toful is sometimes smooth but sometimes lumpy or thorny. At times it is absent, and sometimes it is in complete.

Note: The following index focuses on defining species already observed in the Eastern Mediterranean or expected to be present. There may be additional species that do not appear in our key.

Drowing: A single short central-stemmedA crawling holdfast withA single central-stipe holdfast. several stipes. holdfast.

 Cystoseira rayssiae Smooth toful (left) and compact holdfast Spiny toful (right). and smooth toful.

 

Key to species

1. The ‘stalk’ creeps. The alga develops mainly on soft sediment ®  2

*1.  The ‘stalk’ does not creep but is erect                                       ® 3

2.  The branches are flattened, delicate with a central vein, mainly in the upper part of the plant. Smooth, partial toful (condensation) at the base of the branches. The species is common in deep water (20-150 m) and is endemic to the Mediterranean ...................... Cystoseira dubia = Cystoseira fucoides

*2. The branches are thorny. Partial, thorny toful at the base of the branches. The alga appears in rocky areas covered in sediment or sandy substrate ………………………………......................................... Cystoseira corniculata

3(1). Single stipe (sometimes short). Plants have toful, distinct condensation at the base of the stipe, the toful surface is flat. The holdfast is a single unit (compact, not split) ................................................................ ® 4

3*. Multi-stiped plants, no toful at the base of central branches ................. ® 7

4.  The toful at the base of the branches is smooth, remaining on the plant after branches are shed. The species seems endemic to the Israeli coast............................................................ Cystoseira rayssiae

*4.   The toful is not smooth .................................... ® 5

5. The toful is thorny. Central branches are flattened and lack thorns ..................................................................... Cystoseira platyclada

*5.  Branches are cylindrical ..................................................... ® 6

6.  The central stipe is singular and very short, making the stipe hard to locate. Near the stipe , branching is evident and usually two-directional. The toful is thorny. The ‘leaves’ resemble thorns, and two or more can be seen emanating from the same place along the central axis. The fruit organs (conceptacale), the cryptoblasts (holding hairs) do not grow along the axes of the ‘leaves’ but are sunken in the stipe

 ........................... Cystoseira spinosa var. squarrosa = Cystoseira squarrosa

*6.  The plant has only one long and definite stipe. The fruit organs (conceptacales) and the cryptoblasts appear all over the plant on the stipe and within the axis of the ‘leaf’. The ‘leaves’ are not arranged in pairs

................................................................................ ® Cystoseira spinosa

7(3).  The holdfast is made of one (compact) unbranched segment. Several short stipes. The branches are flattened smooth and without thorns. No apex is evident among the central branches

    Cystoseira compressa = Cytoseira fimbriata = Cystoseira abrotanifolia

*7.  The branches are cylindrical or some are partially so, and some are flattened....................................................... ®    8

8.  Some branches are flattened, and some are cylindrical. The central axis and the central branches are covered with irregular warts and projections. The thallus surface is darkly-spotted with what are, in fact, cryptoblasts (cavities in the thallus containing hair). Air vesicles (when apparent) are smaller, singular and concentrated in the upper part of the plant ............................

             Cystoseira schiffneri = Cystoseira discors = Cystoseira ercegovicii

*8.  Branches are cylindrical ............................................... ® 9

9.   The stipe is elongated, measuring 10-15 cm. The apex is rounded and decorated at the edge with several thorns. The stipe ends in small, soft and rounded branches lacking thorns. At the end of the stipe there are fist-like protrusions. A delicate plant that inhabits places where the water flows slowly   ………………………………………………...................... ® Cystoseira crinite

*9.   The stipe is shorter than 5 cm .......................................................... ® 10 10.  The number of stipes measuring 3-4(6) cm is distinct. The stipe is smooth. The apex is evident among the ‘stalks’, thornless and smooth, and resembles a club. The species lives in shallow water, and tidal pools  .................................................................... Cystoseira barbata

*10.  The holdfast is a single unit (compact). The stipe is short (less than 5 cm). The branches are covered with thorns. The plant is common to beaches exposed to strong wave activity, in the Eastern Mediterranean and in other places ....................................................................  Cystoseira amentacea.