Relationships between environmental conditions and phytoplankton in the Mellah lagoon (south western Mediterranean, Algeria), with an emphasis on HAB species Mohamed Anis Draredja1,4*, Hocine Frihi2, Chahinez Boualleg1, Anne Goffart3 & Mohamed Laabir4 1 Laboratory of Aquatic and Terrestrial Ecosystems, University of Souk Ahras, Algeria 2 Laboratory of Marine Bioresources, University of Annaba, Algeria 3University of Liege, Oceanology, FOCUS Research Unit, MARE Centre, Liege Sart-Tilman, Belgium 4MARBEC, IRD, Ifremer, CNRS, University of Montpellier, France *corresponding author’s email: [email protected] Abstract A bi-weekly monitoring of environmental parameters and microphytoplankton assemblages was conducted in the well-preserved Mellah lagoon ecosystem (south western Mediterranean). Sampling was performed at 3 stations in 2016. We aimed to study the evolution of the phytoplankton community with a focus on harmful species in relation with the environmental characteristics. Phytoplankton of Mellah Lagoon was characterized by a mixture of marine, brackish-water and freshwater taxa. In all of the stations, 227 species of phytoplankton were identified (160 diatoms and 53 dinoflagellates). The overall mean phytoplankton abundance was higher at station A (2.24·105 cells l-1, early September) and B (2.98·105 cells l-1, early October) near of marine inputs, compared to station C (1.73·105 cells l-1, early June) located in the south of the lagoon. Diatoms dominated in spring and dinoflagellates developed in summer and early autumn in the Mellah. The dynamic of the phytoplankton in Mellah was influenced by temperature and salinity. For the first time, a number of potentially toxic species have been identified, including 2 diatom species: Pseudo-nitzschia delicatissima-group (max.: 2.52·103 cells l-1), Pseudo-nitzschia seriata-group (max.: 700 cells l-1) and 6 dinoflagellate species: Alexandrium minutum (max.: 1.42·103 cells l-1), Alexandrium tamarense/catenella (max.: 1.35·103 cells l-1), Dinophysis acuminata (max.: 180 cells l-1), Dinophysis sacculus (max.: 120 cells l-1), Akashiwo sanguinea (max.: 7.20·103 cells l-1), Prorocentrum lima (max.: 110 cells l-1). Even the abundances of the HABs species were relatively low in Mellah lagoon, they could potentially form blooms in the coming decades at the favor of warming and trophic status changes observed in Mediterranean marine systems. Monitoring program of HABs species must be established to gain more insight in the development of potentially toxic species and the toxins produced. Keywords: phytoplankton, HABs species, structure, Mellah lagoon, south western Mediterranean Introduction The lagoons are singular ecosystems, zones of closure of many aquaculture plants (mussels, transition between land and sea. Lagoon oysters, clams). Indeed, some phytoplankton environments constitute about 13% of the world's species (mainly dinoflagellates) produce powerful coastlines (Larras 1964; Barnes 1994). toxins that can be concentrated in the food chain The intensity and frequency of harmful mainly by filtering molluscs. The toxins phytoplankton blooms in coastal ecosystems has accumulate in the tissues of filtering bivalves up to continued to increase (Glibert et al., 2005; sometimes lethal concentrations for humans. Anderson et al., 2008; Heisler et al., 2008). The The Mellah Lagoon, the only lagoon ecosystem in multiplication of episodes of toxic algal blooms Algeria with its environmental and economic and their health and economic consequences justify interests, is a site to explore further. Fish and the rise of research on this phenomenon. In recent shellfish farming are practiced in this lagoon. The years, harmful algal blooms have caused great phytoplankton of this ecosystem has been studied economic loss to fisheries and aquaculture because only in one occasion (Draredja, 2007). The of public health problems caused by toxic objective of this work is to study the evolution of dinoflagellates (Matsuoka & Fukuyo, 2000). The the microphytoplankton community with a focus development of toxic species leads each year to the Ph. Hess [Ed]. Harmful Algae 2018 – from ecosystems to socioecosystems. Proceedings of the 18th International Conference on Harmful Algae. International Society for the Study of Harmful Algae, 2020. 214 pages. 64 on Harmful Algal Blooms (HABs) species in Mediterranean lagoons (Dell’Anno et al., 2002; relation to the environmental conditions. Bernardi-Aubry et al., 2004; Ifremer, 2006), Mellah appears less rich in nutrients. So we class it Materials and Methods among Mediterranean lagoons meso oligotrophic (OECD, 1982). The low level of nutrients of the of The Mellah lagoon is located in the northeast of the Mellah lagoon waters results in a moderate Algeria (36°54'N 8°20'E) far of all sources of seasonal biomass in chlorophyll-a (between 0.70 pollution, within a protected natural reserve (Fig. and 5.45 µg l-1) (Table 1), compared to other 1). The lagoon (8.65 km2) communicates with the Mediterranean lagoons (Triantafyllou et al., 2000; sea by a long and narrow channel. During 2016, a Nuccio et al., 2003; Bernadi Aubry & Acri, 2004; monitoring program of microphytoplankton and Solidoro et al., 2004). physico-chemical parameters (temperature, salinity, dissolved oxygen, pH and suspended matter) was carried out fortnightly in 3 representative stations in the lagoon (Fig. 1). France Italy Spain Mediterranean Sea Algeria Morocco Tunisia N N A Mellah B lagoon Mellah C 1Km lagoon Fig. 1. Location of the Mellahlagoon and position of sampling stations. Nutrient (NO3, NO2, NH4, PO4) and Chlorophyll- a analyses, were carried out by spectrophotometry. Microphytoplankton was sampled in surface waters, where a volume of 50 liters of water was filtered through a plankton net (20 µm mesh size) and fixed with neutralized formalin (4%). Both the identification and counting of phytoplankton (cells l-1) were performed with an inverted light In total, 227 microphytoplankton species belonging microscope (Leika 750 PM). mainly to diatoms (160 species) and dinoflagellates Statistical analyses were performed using R, (53 species), were inventoried in the Mellah version 3.4.2 (R Core Team, 2017) developed for lagoon. In this list of species, we found height Windows by (Ihaka & Gentleman 1996). potentially HAB species (2 diatoms and 6 dinoflagellates) (Table 2). The lagoon was Results and Discussion characterized by a clear dominance of diatoms The seasonal values of environmental parameters (63%) compared to dinoflagellates (37%). This are reported in Table 1. Unlike most trend is observed in many Mediterranean lagoons (Tolomio et al., 1999; Bernardi Aubry & Acri, 2004), but also in Algerian coastal marine waters 65 species) is specific higher lagoon Mellah microphytoplanktonthe of oligotrophy meso the Despite than r remoteness fromany source of pollution. some distinguished by its eutrophic meso oligotrophy, due to its which are unl eutrophic, the 0.43), to (0.16 salinity and 0.56) to Mellah lagoon were positively correlated is with temperature (0.46 lagoon Mellah the in densities microphytoplankton The Pearson the lagoon. analyses II 2, showed (Fig. prospected stations three the in similar very is that syndromes. The distribution of these HAB species the nitzschia Prorocentrum lima, Dinophysis poorly represented (< 700 cells l Other HAB species were present (Benedetti,waters 2016; Karidis&Kitsiou, 2011). (Table trophic status changes blooms affecting in the future at Mediterranean the favor of warming and relatively low, but they abundance could potentially of form winter thes and spring respectively (Fig. (1.35·10 2, II). The early June) and as et al., 2017). (Xu effect hemolytic a with models several to toxic were noted in summer (Fig. 2, II). This species is sanguinea Proliferations of harmful Ju species as (173.13 St.C to compared inputs, (298.41·10 (223.99·10 phytoplankton abundance was (Frehi, higher 1995; at Illoul, 2014). St.A The overall mean phytoplankton diversity. species quality of the Mellah and Mediterranean Sea lagoon to stabilize the between exchange water the waters improve to established and A to regular increase dredging Mellah waters salinityduring theseason. summer of the the warming cha of the waters and the increase of the The proliferation of dinoflagellates coincides with Mediterranean lagoons. ne) under Alexandriumminutum ike the majority of Mediterranean lagoons, ), hence the role of the hydrodynamic action in action hydrodynamic the of role the hence ), 3 cells l cells spp. at St.C (7.20·10 3 3 land influenceland (Fig. 2,I). cells l cells l Other potentially neurotoxic species , responsible of DSP and ASP - 1 , early February) were observed in observed were February) early , A. tamarense/ - - 1 1 , early October) , early September) and St.B e HAB species remained 2000 Akashiwo sanguinea (1.42·10St.B at 1800 Alexandium tamarense/catenella St.A 3 ) 1600 Alexandrium minutum cells l 1 - 1400 1200 catenella at St.A ·10 1000 - 1 sp. 800 ). They included - p 1 ichness ichness (227 nnel nnel must be 600 <0.05. 3 , end of June), HABs (cells l 400 l cells and Pseudo 200 near marine 0 Akashiwo 3 J J J J J J F F S S A A A A O O N N D D - - - - - - - - - - M M M M cells l cells Finally, - - - - - - - - - - - 9 - - - - 6 9 1 6 7 8 5 3 28 7 9 21 10 24 24 10 25 2) but 25 22 22 19 21 , early , 21 23 ( - I 2500 Akashiwo sanguinea 1 - ) St.B , Alexandrium tamarense/catenella ) 2000 Alexandrium minutum 1 - 1500 1000 ( ( microphytoplankton Fig. 2. II HABs (cells l 500 ) in the Mellah waters (2016). waters Mellah in the ) 0 Abundance J J J J J J F F S S - - - - - - A A O O N N D D A A M M M M - - - - - - - - - - - - - - 9 - - - - 6 9 7 8 5 3 6 7 9 21 10 24 24 10 25 28t 22 22 19 21 25 21 23 1400 Akashiwo sanguinea Alexandrium tamarense/catenella 1200 Alexandrium minutum ) (cells l (cells 1 - 1000 St.C I 800 ) and harmful species (HABs) (HABs) species harmful and 600 - 7200 1 ) of total ) of total 400 HABs (cells l 200 0 J J J J J J F S F S - - - - - - A A A O N N D D A O M M M M - - - - - - - - - - - - - - 9 - - - 6 - 9 6 5 3 7 8 7 9 21 10 24 28 25 24 10 25 22 22 19 21 23 21 ( II 66 ) Table 2.