Algae are of paramount ecological importance in the water body as it represents the food source for the higher trophic levels, and they are the most productive photosynthetic organisms in the world (Kasting et al. 2002). However, sometimes this food, stimulated by nutrient inputs (agricultural or domestic discharges also rich in chemical, organic or mineral contaminants), constitutes a major problem (ecological and sanitary) both for the population, which uses the water resources, and for the fauna and flora for which water represents the living environment (Viessman et al. 2009). For this reason, regular monitoring, aimed at surveillance and control of the development of this seaweed, is necessary.
Algae are chlorophyllous organisms capable of occupying all types of environments, although they are abundant in fresh and marine waters, on damp ground and even on snow. They also exist in all humid environments and tropical regions, and can be found even on the walls of buildings. They can be endophytes of certain protozoa or metazoa. Some algae associate with fungi and form lichens. They are divided into 6 large phylums according to the nature of the pigments and cell reserves; these are Cyanophytes, Chlorophytes, Euglenophytes, Chrysophytes, Rhodophytes and Pyrrhophytes (Iltis 1980). In this work we are interested in Seaweed. It is limited to tidal, photic and benthic areas and contributes to 10% of total marine productivity (Seckbach 2010). Algae are the main habitat generators. Changes in global temperature and ocean chemistry have been associated with increased concentrations of greenhouse gases, which have had an effect on biological systems, causing large-scale changes. In addition, these algal ecosystems contribute to the development of global socio-economic activities through their use in food, agriculture and industry. Algae are a bioindicators of ecosystem health and integrity because they form the basis of most food chains in aquatic environments, and of the properties of their components. They are used in many sectors: Agriculture and horticulture, the exploitation of algae in agriculture is also a way of adding value to algae. At present, we are moving towards the use of extracts that not only act as fertilizers, but also accelerate growth and protect crops, limiting the antifungal activity (Nafis et al. 2021). Farmers use algae to strengthen plants natural defences, instead of using, for example, pesticides. These new products, commonly known as SDN (Natural Defense Stimulator), could eventually replace certain phytosanitary treatments (Jaulneauet al. 2010). In the medicinal and pharmaceutical field, through their anti-amyloidogenic role (Vasarri et al. 2020), antibacterial, antiviral, antimyco-bacterial, antiplasmodial, antiprotozoal, antifungal and strongly anti-inflammatory properties (Allmendinger et al. 2010; Oumaskour et al. 2013; Spavieri et al. 2013; khelil-Radji et al. 2017; Nafis al. 2021), having antitumor and antioxidant potential on human colorectal ad-enocarcinoma cells (Zbakh et al. 2014). Indeed, green algae contain a family of sulphated polysaccharides called ulvanes, which are the subject of several studies aimed at highlighting their beneficial activities in protecting plants against pathogens (Misurcova et al. 2012). Seaweeds are also used in the pharmaceutical industry (Trono, 1973; Febles et al. 1995; Lima-Filho et al. 2002; Ely et al. 2004; Inci et al. 2006). In cosmetics, Algae are an excellent source of minerals with a high affinity for skin cells. Seaweeds as source of dyes, of aromas and of fragrances (Couteau and Coiffard 2016). Algae extracts are used as active ingredients for hydrating and anti-ageing products (Couteau and Coiffard, 2016), thanks to the wealth in complete supply of active elements nourishes, stimulates epidermal cells and promotes skin renewal. For example, minerals contribute to the good balance and vitality of the cells, notably by participating in the activity of numerous enzymes (Nahas et al. 200; Cardozo et al. 2008; Li et al. 2009). Renewable energy, its special interest was devoted to micro- and macro-algae for biofuel production (Chisti 2007; Hankamer et al. 2007). At present, an industry is developing to produce biofuels from lignocellulose, so-called second and especially third generation biofuels (Didderen et al. 2008). According to El Asri et al (2017a and b), the Caulerpa prolifera, Gracilaria bursa-pastoris, Colpomenia sinuosa and Alsidium corallinium species in the Marchica lagoon present an exploitable energy reserve. The alginates salts extracted from algae are of great interest in the textile industry, they play an essential role in fixing colours in a fabric (Pereira and Cotas 2020). This alginate allows better penetration of the colour into the textile fibres but does not prevent the sun's rays from progressively reducing contrasts. Whereas in environment, algae play an important role for biodiversity, nutriment cyclique and ecosystems services in nearly all environment (Preirna and Neto 2014) and in maintaining the balance of aquatic environments, as primary producers and an important source of oxygen for the links in the ecosystem's food chain. As pollution indicator organisms, some red algae (Alsidium sp., Sargassum fluitans) (Figueira et al. 1997; Matoir et al. 2015), green algae (Ulva rigida, Chaetomorpha linum, Caulerpa prolifera, Enteromorpha intestinalis, Chaetomorpha linium, Ulva lactuca) (Kaimoussi et al. 2004; Chouba et al. 2010; Rahmouni et al. 2016) and brown algae (Ascophyllum nodosum, Fucus vesiculosus (Kuyucak et Volesky 1988; Holan et Volesky 1994; Fourest et Volesky 1997) are used to examine and assess the state of contamination by certain heavy metals. Because of their ability to bio-accumulate pollutants, these algae often considered as bioindicators of pollution and could be used in phytoremediation, mainly the species of Chaetomorpha aerea (Aknaf et al. 2018) for chlorophyceaes, while for rhodophyceaes : Alsidium corrallinium and Gracilaria gracilis which have a higher level of protection against climate changes (Aknaf et al. 2020). This work was carried out in parallel with other parameters, namely sedimentological, biological and chemical (Aknaf et al. 2015, 2018 (a, b), 2017(a, b), 2021).
The purpose of this research was to evaluate the spatial and temporel distributions of the algae inventory of the Marchica lagoon, as well as their in relation to environmental variations and the dominant species distribution of Seaweeds in lagoon after opening the new pass in 2011.