Diatoms diversity and dynamics in a southern Mediterranean lagoon (Mellah, Algeria)

Abstract

The composition and distribution of diatoms were studied using a biweekly sampling performed in three representative stations in the Mellah Lagoon (South Western Mediterranean, Algeria), during 2016. In total, 160 diatoms species-belonging to centric species (52 species) and pennate species (108 species)-were inventoried. The relative abundance of the pennate forms (67.50%) is clearly higher compared to the centric forms (32.50%). The blooms of diatoms are represented by 3 species: Chaetoceros constrictus Gran, 1897 with up to 15000 cells.L-1 (end of May), Chaetoceros sp. with up to 178320 cells.L-1 (early October), and Nitzschia longissima (Brébisson) Ralfs, 1861 with up to 200640 cells.L-1 (early September). Proliferations of three potentially toxic species: Pseudo-nitzschia group delicatissima (Cleve) Heiden, 1928 (2500 cells.L-1), Pseudo-nitzschia group seriata (Cleve) H. Peragallo, 1899 (700 cells.L-1) and Thalassionema nitzschoides (Grunow) Mereschkowsky, 1902 (210 cells.L-1), requires regular monitoring of this ecosystem where the exploitation of the shells is practiced. The diatom populations seem to be structured showing diversity (H') and equitability (J') indices reaching 4.56 bits.cell and 0.98 respectively, with the exception of springsummer and summer-autumn transition periods. high biological productivity and biodiversity (Knoppers, 1994). However, the lagoons are very sensitive environments, fragile and extremely vulnerable, in relation to the organization of their living and non-living components which depends on the interaction between the natural components of the marine and continental areas (Dufour et al., 1994). Due to the wide variability of their physical, chemical and biological parameters, coastal lagoons are generally unstable environments. The

Environmental parameters and diversity of diatoms in the Aïn Dalia dam, Northeast of Algeria

“…Similarly, the authors have shown the dominance of genus Diatoma with a rate of 42.37% as compared with the genus Nitzschia (17.5%) found at the Rhiou river, since the genera Nitzschia et Navicula are predominant in Malah river, along with rates of 63.87% and 18.5% respectively. However, the study of Draredja et al (2019a), in the Melleh lagoon, indicates that the dominant genus is Nitzschia. The study of Chabaca et al (2020), in the Oubeira lake, indicated that the genera Cyclotella and Nitzschia dominated the lake.…”

“…However, the study performed by Nehar (2016) has revealed that the results of settlement structure from El-Hammam and Chelif rivers (North-est Algeria) provided generally, low mean values. On the other hand, Draredja et al (2019a) reported that the diversity of populations of diatoms in the Mellah is up to 4.56 bits.cell -1 and with a of regularity of 0.98, and thus suggesting populations of structured diatoms for a single period of the year (winter and late spring). However, the rest of the cycle is characterized by unstable species composition.…”

Fish food-web structure of a southern Mediterranean lagoon (El Mellah Lagoon, Algeria): what we can learn from stable isotope analysis

“…8.6 km 2 . With an mean depth of 3.5 m (Messerer, 1999;Draredja, 2007), EML connects to the sea via a channel ca. 870 m long, 20 m wide, and 0.5-2.0 m deep (Draredja, 2007).…”

“…With an mean depth of 3.5 m (Messerer, 1999;Draredja, 2007), EML connects to the sea via a channel ca. 870 m long, 20 m wide, and 0.5-2.0 m deep (Draredja, 2007). It receives freshwater from three intermittent rivers (wadis): El-Mellah and Bélaroug in the south and R'Kibet in the north-west.…”

“…EML has low human pressure but significant economic interest for fishing, aquaculture and tourism (Draredja, 2007). Due to limited exchange between EML and the sea, the EML's hydrology is strongly influenced by precipitation, evaporation and freshwater inputs (Guelorget et al, 1989;Ounissi et al, 2002).…”