models seaweeds

Model seaweeds

Solieria chordalis

Solieria chordalis (J. Agardh) C. Agardh is a red alga of the order Gigartinales, family Solieriaceae. This species is found along the coasts between Morocco and the south of England; along the French shoreline, it is observed from Vendée (Ré Island) to the Côtentin peninsula via the Gulf of Morbihan and the Bay of Brest (Brittany).
Solieria chordalis consists of a firm, cylindrical, red-pink thallus with a maximum length of 15 to 20 cm and a diameter of 0.5 to 2 mm. Its thallus develops from a fibrous basis composed of entangled filaments, haptera, that act as holdfasts around the anchoring point of the seaweed. The main axes are unevenly branched; over the growth period they are covered with small protuberances that further develop into branchlets, which can detach and re-attach to the substratum to develop into a new plant. This mode of reproduction seems to predominate in the population of Solieria chordalis within the Bay of Brest. Its life cycle is trigenetic, haplodiplophasic and isormorphic.
Solieria chordalis is a perennial seaweed that lives in shallow waters, i.e. 0 to -5 m below the low-tide level, on various substrates such as mud, gravels, shell residues and even calcareous algae constituting maerl. This species settles in more or less sheltered and sometimes turbid areas where environmental changes can be quite important.
Solieria chordalis is used as a model by the scientists of the LEBHAM-group. Their investigations are focused on carrageenans and adaptation of this species to various environments through metabolic changes occurring under controlled culture conditions.

Grateloupia doryphora

Grateloupia doryphora (Montagne) Howe is a cosmopolitan red alga of order Halymeniales and family Halymeniaceae. It is indeed found in the Atlantic Ocean along the coasts of America, Africa as well as in the Pacific Ocean along the shoreline of Peru, Japan, New-Zealand. This exotic species, maybe originating from Indo-Pacific, was first found in the South of France (Etang de Thau) in 1982. In 1989, it was first identified in Brittany at Fort-Bloqué (Morbihan), and then in 1992 at Carantec (Finistère). Its identification in places like Le Croisic (where it was eradicated by the Erika oil spill), Concarneau, Brest, Granville and Cherbourg confirms that this newly-introduced species is spreading.
G. doryphora is one of the most polymorphic among the red algae. It is composed of a thallus, easily identified because of its soft and gelatinous texture, that grows from a short stipe held by a reduced holdfast. One or several single or branched blades rise from one holdfast; the blades are sometimes spiked with many marginal proliferations. G. doryphora thallus can reach 185 cm in length and 30 cm in width and is the biggest red alga ever found in Europe.
Its life cycle is trigenetic and dimorphic.
Over the last two years, G. doryphora has progressively colonised the whole intertidal zone at Fort Bloqué. Its settlement started from the middle of the intertidal zone down to the limit of the subtidal zone to finally colonise the basins at the top of intertidal zone. However, its development has been the most important at the mid-tide level, especially in the flows enriched in freshwater (salinity within 20-15 ‰ at low tide) where plants grow quickly in size and number to reach density up to 200 plants/m². Its adaptation to quick changes in salinity together with its dispersal over the whole intertidal zone suggest that this alga has strong physiological capabilities.
Grateloupia doryphora is studied within the LEBHAM group to carry out investigations on its ecology, because of its recent introduction along the coasts of Brittany, and on its bioactive substances, especially osmolytes, that allow this species to colonise environment under variable salinity conditions. Please, inform us of its presence.

Turbinaria ornata

Turbinaria ornata (Turner) J. Agardh is a brown alga of the order Fucales and family Sargassaceae. The genus Turbinaria is widely distributed in the flora of tropical and subtropical areas including the North-East of Australia, the Red Sea, India, Indonesia, Japan and the West Indies. In French Polynesia, however, T. ornata is the only species reported.
Turbinaria is characterised by a cladomian structure, previously described in the higher thallophytes. T. ornata consists of a main, tough and brown to light brown axis that carries short side-branches, pleuridae, which give the seaweed a cylindrical shape.
Its life cycle is monogenetic, diploid and characterised by the permanence of sporophytes on rocks.
In French Polynesia, T. ornata shares the intertidal and subtidal zones with other brown algae. This species has been observed in places extending up to the external slope of the reef and at a 10-m depth. According to Payri (1982) it is a dominant species all over the reef where it is widely distributed on substrates, like dead corals and rocks. This species constitutes typical mats around the high islands. Over the last years, it has been considered in these islands of the Pacific Ocean as an invasive species because of a drastic increase in biomass.
Within the LEBHAM group, this brown algua is the subject of collaborative studies carried out with the French University of Pacific (Marine Ecology Laboratory, Professor C. Payri) and dealing with biologically-active substances for potential applications in medicine- and pharmacy-related fields (cosmetics, for example). This valorization project has led to a partnership with a Polynesian company, CAIRAP, (CIFRE-funded fellowship).

Sargassum mangarevense

Sargassum mangarevense (Grunow) Setchell is a brown alga of the order Fucales and family Sargassaceae. About 400 very polymorphic species of the genus Sargassum have been inventoried world-wide. Nine of them have been found and described in Polynesia. This genus is widely distributed in warm and temperate waters, and especially in Indo-Pacific areas and Australia. For many years it has focused attention because of the geographical spreading of Sargassum muticum in the USA along the Pacific Ocean, and in Europe along the Atlantic Ocean, respectively.
S. mangarevense is composed of i) a yellow-light brown thallus constituted of a perennial part consisting in a disc, which allows the seaweed to attach to the substrate, and a main axis, i.e. low-growth stipe, ii) an annual part made of side-branches growing from the main axis and composed of either foliose proliferations, i.e. the fronds, or fronds and air bladders, or fronds, air bladders and reproductive organs. The thallus can have a length of 48 cm.
This species is also characterised by a monogenetic, diploid life cycle; the sporophyte remains all over the year on the rock.
In the French Polynesia, S. mangarevense is mainly found on the ridge of the fringing reef where it constitutes an algal belt in a high-hydrodynamism area regularly emerging at low tide. In the lagoon, it colonises the outcropping part of the barrier reef. Like Turbinaria ornata, over the last years S. mangarevense has been considered as an invasive alga because of drastic increase in biomass; it is also the subject of valorization studies carried out in partnership with the French University of the Pacific.

Undaria pinnatifida

Undaria pinnatifida (Harvey) Suringar is an annual brown alga of the order Laminariales, family Alariaceae. In Winter and Spring its length can be of 1 to 2 m.
This genus is endemic in Japan and extensively cultivated in South-East Asia (Japan, Korea, China) where it is named Wakame and widely consumed as food.
It was found in 1971 in the waters of Etang de Thau, near the Mediterranean Sea; in 1983 it was introduced in the Atlantic Ocean, on the coasts of Brittany, by the scientists of IFREMER. Cultivated in Brittany, it is nowadays found in several areas of France, United-Kingdom, the Netherlands, Spain and Italy where it seems to get acclimated (Floc'h et al., 1996). It has also been introduced in New-Zealand, Australia and Argentina.
Undaria pinnatifida is the subject of investigations conducted within the LEBHAM group to get insight on the vectors involved in its spreading and on its adaptation capabilities (Lamarque et al., 1999). This species lives in the first meters below the low-tide level or near the surface (floating objects). When young and because of its distinct midrib, it can be confused with Alaria esculenta, though the shape of its blade with lobed sides and its undulated sporophylles at the bottom of stipe make it seem quite different. Undaria can be found in river mouths and harbours. Please, inform us of its presence.

Marine Cyanobacteria from tropical origin "Kopara"

Microbial mats consist of usually stratified structures composed of several layers of different colours. These very typical sequences are found in saline or hypersaline lagoons distributed over temperate to tropical areas. They find their origin in the growth of microorganisms, i.e. Cyanobacteria and anaerobic phototroph bacteria, vertically distributed with respect to a 3-component gradient (light, oxygen and sulfides). Bacteria own specific pigments that allow them to grow in deep-waters, even in anoxic environments often rich in sulfide. Their ecological role is important because, thinks to photosynthesis process, they can recycle some organic compounds and limit the release of toxic sulfide in the areas where it is produced. In addition, in biotechnology, bacteria and Cyanobacteria are looked for their sulfo-oxidizing action and/or for their production of specific carotenoids used as dying agents in the food industry. In French Polynesia microbial mats are growing on the coral reefs of atolls and islets (motu) of some high islands of the Society archipelago. Their thickness depends on locations and environmental conditions and can range from a few millimetres to several tens of centimetres. In the Tuamotu archipelago these reddish and gelatinous microbial mats are named 'Kopara'. Years ago this natural resource was consumed when food was scarce; it seems to be still used for feeding in some archipelagos of the central and North-West Pacific Ocean. It was also employed as healing plaster. Because of some of its properties, especially the nutritional and medical ones, Kopara may be of interest in various fields, e.g. medical and paramedical ones (antibacterial and healing properties), food-industry (carotenoids used as dying agent) and pedology (stabilisers).

Whatever the type of pond where Kopara is found its structure is quite homogeneous; it consists of a vertically-laminated microbial mat. Like most of microbial mats it is dominated by some microorganisms characterised by their functional groups: cyanobacteria (those of the genus Phormidium along with Scytonema, Schizothrix and Chlorococcales), sulfurous photosynthetic bacteria like, for example, Chromatium and Thiocapsa, non-sulfurous red bacteria (PNSB among which Rhodospirillum and Rhodopseudomonas/Rhodobium/Blastochloris) and sulfate reducers (mainly Desulfovibrio). Most of the ponds have a common characteristic: they are devoid of living organism. One should, however, note the presence of fish like Tilapia whose food may eventually consist of the upper microlayer of cyanobacteria. This lack of living organism may be related to the very high levels in sulfides that may result from the low, or even null, amounts in iron within these mats which, thus, makes the trapping of sulfides quite impossible.

Model halophytes

Suaeda maritima (L.) Dum.

A prostrate to erect ± glaucous or red-tinged glabrous annual 7-30(-60) cm. Leaves : 3-25 mm x 1-2(-4) mm, demi-terete, acute or subacute. Flowers : 1-3 together in small axillary cymes. Stigmas : 2. Seed : 1· 1-2 mm diam., biconvex, nearly circular in outline but with a small curved beak, black, shining, with fine reticulate sculpturing, horizontal. Flowers : july-october. Fruits : august-november. Germination : spring. 2n = 36.

Native. In salt-marshes and on seashores, usually below high-water mark spring tide, common.

Atriplex portulacoides L.

A very small shrub up to 80 or rarely 150 cm. Rhizome short, creeping. Stems decumbent, branches ascending, terete below, angled above. Lower leaves opposite, shortly (5-10 mm) petioled, elliptic ; upper linear, entire, obtuse or appiculate. Infloration of terminal and axillary compound spikes ; partial infloration dense. Fruits sessile. Bracteoles in fruits 3-5 mm long and rather broader, obteloid, united 2/3 of the way from the base, usually 3-lobed. Flowers : july-september. Fruits : september-october. 2n = 36.Native. In salt-marshes, especially fringing channels and pools, ordinarily flooded at high tide.