|Keywords||Algae, endemic, Endangered species, introduced and invasive|
Morocco, with its expansive coasts, is particularly well provided in marine and coastal ressources, of which algae constitutes the principal marine flora. These are thallophytic plants (nondifferentiated simple vegetative splint in the roots, stems and leaves) autotrophic (provided of assimilator pigments and thus capable of effectuating photosynthesis). Their presence in deep waters is thus limited by the absence of light necessary for photosynthesis (certain sciaphlic species are found at depth going until 200 m.). They synthesize organic matter that feeds a great part of the marine fauna (fish, mollusks, crustaceans...) and are thus the principals responsible for the primary production in marine zones, notably the phytoplancton of which the richness determines largely the quality of fishing. Like superior plants, they get rid of oxygen directly used by marine species. They also permit the clarification and auto-purification of water by recuperating nutritive elements in suspension and by liberating (by certain macroalgae) bacterial substances.
From the economic point of view, algae are used to multiple ends: as alimentation (particularly rich in iodine), in agriculture as fertilizer and fodder, in the alimentary industry and pharmaceutical one (Agar, alginates, carraghenanes) in textile and other domains.
Algae are connected at different levels:
The supra coastal level is limited between aerial vegetation and the medium level of high seas of live waters.
- Coastal level with three horizons: superior, medium and inferior. It is the part of the coast exposed to rather regular alternations of immersion and submersion.
- The infra coastal level is situated below the inferior level of the low seas of live waters. It is subdivided in two below-levels, one superficial (photophile, affinity of species for light) and the other deep (sciaphile; affinity of species for shade).
In the Mediterranean, this zoning is much less clear than in the Atlantic Ocean because of the weak amplitude of tides and of coastal relief.
We distinguish among the algae benthic species fixated at the substratum or lying on the depth of the sea and the pelagiac species that swim or float in suspension in water like unicelluar microscopic algae or phytoplancton.
Moroccan coasts harbour a great richness in algae species of economic and ecological interests, but this richness is far from being completely inventoried; great gaps are left to be filled in: several rocky inaccessible zones on the Atlantic have not yet been studied; Saharan province coasts have yet to be explored; many systematic works have not been followed and, at last, numerous cultivated species have not been determined because of the lack of flora necessary for the identification and recognization of these species. The richness of phytoplancton are also still in need of evaluation.
Macroalgaecal flora is at a total of 489 species, of which 303 are Rhodophyceae (red algae), 99 are Phaeophyceae (brown algae) and 87 are Chlorophyceae (green algae). The Cyanophyceae (blue procaryotic algae) are represented by 12 species and the Liliopsidae (Phanerogames or marine Monocotyledones) by 4 species. With 381 species, the Mediterranean facade is slightly richer than the Atlantic coast (323 species).
Among algaecal flora in the strict sense, we can disclose a certain affinity of species for each type of facade; we have thus 108 Atlantic species, 166 Mediterranean, and 255 Atlantico-Mediterranean.
The examination of phytogeographic origins of known algae species shows that several taxa of Atlantic origins have passed the Straight of Gibraltar and have installed themselves in the Occidental Mediterranean and particularly on the Moroccan facade, the Peak of the Three Forks constituting the eastern limit of the propagation of these species. Among these species, the Gelidium sesquipedale, Gigartina pistillata, Fucus spiralis, Cystoseira humilis, C. gibraltarica and C. tamariscifolia. Some taxa of tropical origin not found on the Atlantic coast are present on the Mediterranean like: Sargassum acinarium, Acetabularia acetabulum, A. calyclus, Dasycladus vermicularis, Halimeda tuna, Udoteae petiolata and Caulerpa prolifera. Among the strictly Mediterranean species, one must note: Rissoella verruculosa, Cystoseira mediterranea, C. crinita, C. spinosa, C. stricta and the phanerogame Posidonia oceanica.
One must note that on the scale of the Mediterranean region we have made the inventory of 500 Rhodophyceae, 200 Phaeophyceae and 200 Chlorophyceae. Morocco as a Mediterranean country occupies thus a convenient place as to the specific algae richness, even as important sectors of its coasts have not been yet explored.
The brutal apparition of an algae species in a region where it was unknown before results in general of an introduction, most often because of an anthropic origin. In Morocco, no study has yet been realized to the present in this case.
Among the known cases of recent introductions: Rhodophyceae (red algae): Antithamnion algeriensis and Asparagopsis armata, respectively originating from the indo-pacific zone and Australia. Chlorophyceae (green algae): Codium fragile, Acetablularia calyculus and Caulerpa racemosa. Phaeophycees (brown algae): Colpomenia perigrina.
Even though these introductions do not seem to have had any particular incidence, neither on the environment, nor on the economic activities of the concerned regions, a scientific policy must be realized so as to limit the impact of all introductions on the specific diversity and the national socio-economic activities.
The acclimatization of a plant into a new ecosystem can result in a true invasion that can lead to the elimination of the indigenous species and their replacements by a monospecific population of the invasive algae. A case of invasion has been found in the Lagoon of Nador (Sebkha Bou Areg) where we have seen the progressive disappearance of Posidonia oceanica, endemic to the Mediterranean, following the proliferation of Caulerpa prolifera and other new species.
On the Moroccan coasts, we inventoried 7 invasive species (of which 6 are in the only Lagoon of Nador) belonging all to Chlorophycees: 3 Ulvacees (Enteromorpha intestinalis, Enteromoropha prolifera, Ulva olivascens), 3 Cladophoracees (Chaetomorpha linum, Cladophora vadorum, Cladophora globulina) and 1 Caulerpacee (Caulerpa prolifera).
Enteromorpha intestinalis is the only species present at the same time in open sea and at the lagoon level; it abound on several sectors of the Atlantic coast, in particular at Jorf Lasfar where it constitutes a monospecific population extending on several kilometers. The other species are contained for the moment on the lagoon level.
The process of invasion, once released, is difficult to stop. The recent multiplication of these species on the Moroccan Mediterranean is thus to be taken into consideration since they are susceptible to modifying the functioning of the coastal and lagoon ecosystem.
We consider here these as endangered species: - species for whom the cycle of development is made with difficulty or very slowly; - species which begun to disappear completely from superficial waters and confine themselves in deep waters because of the degradation of their habitual living area; - species which are pulled (anarchically) manually for industrial exploitation.
Endangered species are up to 21, of which 3 are Chlorophyceae, 7 are Phaeophyceae, and 10 are Rhodophyceae, upon which one must add one Liliopsidee (phanerogame species).
One particularly noticeable case is the progressive elimination of the large algae fields (Laminaria, Sacchoriza and Phyllariopsis) on both the Atlantic and Mediterranean; these species seem to escape superficial waters to descend to the depth (up until 30 m.). Certain endangered red algae are exploited industrially for the extraction of agar-agar. Gelidium sesquipedale, the most sought after species for its use in agar, demonstrates a drastic regression due to its overexploitation and in a certain measure to pollution, even with its great capacity of plant regeneration; its harvest, done before by simple gathering at low tide, necessitates today scuba-diving at lower and lower depth. Concerning Posidonia oceanica, endemic phanerogame, its progressive regression in the lagoon of Nador, which is its favorite site in Morocco, is due essentially to pollution and the apparition of floating species due to this.
Certain of these endangered species could be made the object of an economic value such as Bryopsis (green algae), Laminaria and Sacchoriza (brown algae), and several red algae species.
The Moroccan Mediterranean marine flora contains 2 endemic species: the red algae Rissoela verruculosa which is found between the Peak of the Three Forks and Al Hoceima, with a less dense population at Chaffarines Islands, and the phanerogame species Posidonia oceanica, found at Sebkha Bou Areg (Lagoon of Nador). This last species is today endangered to total extinction because of pollution and the apparition of other species (especially the Chlorophyceae) adapted to the lower waters. These species can either float on the surface thus blocking the passage of light, or invade directly the herbarium at Posidonia, causing its asphyxsiation (especially Caulerpa prolifera). This endemic ‘taxon’, like other species in its family, has a great primary productivity, permitting the clarification of water, retaining nutriants in suspension, and representing an ecological niche for many animal species. Its preservation is thus of great importance.
It is made up of microscopic algae that are either pluricellular and fibrous, or mostly unicellular. Up until today we have inventoried 68 species (estimated number) on a national scale, of which 36 Diatomes, 22 Dinoflagelles, 3 Chrysophyces, 3 Chlorophyces, 2 Xanthophyces and Coccolithophorrides.
The abundance of phytoplancton depends on the temperature of water and its richness in nutritious salts (phosphates and nitrates). Phytoplancton in a large measure assures the primary production which determines the richness of fishing zones.
The greater and greater use of fertilizer in agriculture and detergents has resulted in a rapid augmentation of mineral supplies towards the pouring bassins then towards the coastal waters, which has engendered, in certain sites, especially in the Mediterranean (closed sea), the development of a type of phytoplancton responsable for the red tide ‘bloom’ phenomenon, and the proliferation of species producing toxins (intoxication of bivalves and fish, sometimes fatal for man). It is mostly the Dinoflagelles who are responsible for these two phenomenons; the principal species responsible for the red tides are Gonayaulax polygramma, Gymnodinium sp., Peredinium sp., and Noctiluca scintillans; the intoxication of ‘fruits de mer’ and fish is provoked mostly by the species Dinophysis acuta, as well as by Alexandrium tamarensis.
The red tides can last from two to fifteen days, disappearing rapidly after the exhaustion of nutritious salts, or following hydrological modifications (water stirring) or by strong winds with a change of direction. These red tides are sometimes accompanied by a production of a viscous organic matter of phytoplanctonic origin that can reduce lighting and inhibit the productivity of the ecosystem, with the consecutive reduction of sardine fishing and the degradation of the quality of swimming stations (gelatinous creme on the surface of water, burning toxins at the contact with the skin of swimmers, also provoking respitory problems, with asthma, fever, articular pains, and periorbitales, cutaneous eruptions, etc.).