Seasonal variations of phytoplankton assemblages in relation to environmental factors in Mediterranean coastal waters of Morocco, a focus on HABs species

Benlahcen Rijal Leblad (1) , Rachid Amnhir (1) , Sagou Reqia (1) , Ferdaous Sitel (2) , Mouna Daoudi (1) , Mohamed Marhraoui (1) , Mohamed Karim Ouelad Abdellah (1) , Benoît Véron (3) , Hassan Er-Raioui (2) , Mohamed Laabir (4)

1 INRH - Institut National de Recherche Halieutique [Casablanca, Maroc]
2 UAE - Abdelmalek Essaadi University [Tétouan] = Université Abdelmalek Essaadi [Tétouan]
3 BOREA - Biologie des Organismes et Ecosystèmes Aquatiques
4 UMR MARBEC - MARine Biodiversity Exploitation and Conservation

Studies on phytoplankton and in particular Harmful Algal Blooms (HABs) species in southern Mediterranean waters are scarce. We performed from April 2008 to June 2009 weekly investigations on microphytoplankton community structure and abundance in two contrasted marine ecosystems located in the western Moroccan Mediterranean coast, M'diq Bay and Oued Laou Estuary. Simultaneously, we measured the main physico-chemical parameters. Globally, the two studied areas showed comparable values of the assessed abiotic environmental factors. Temperature and salinity followed seasonal variation with values ranging from 13.5°C to 21.4°C and 31 to 36.8, respectively. Average nutrient values in surface water ranged from 0.7 to 45.76 μM for dissolved inorganic nitrogen, 0.02-2.10 μM for PO 4 and 0.23-17.46 μM for SiO 4 in the study areas. A total of 92 taxa belonging to 8 taxonomic classes were found. The highest number of microphytoplankton abundance reached 1.2 × 10 6 cells L −1 with diatoms being the most abundant taxa. Factorial Discriminant Analysis (FDA) and Spearman correlation test showed a significant seasonal discrimination of dominant microphytoplankton species. These microorganisms were associated with different environmental variables, in particular temperature and salinity. Numerous HABs species were encountered regularly along the year. Although Dinophysis species and Prorocentrum lima were present in both sites, no Lipophilic Shellfish Poisoning was detected for the analyzed bivalve mollusks. Domoic acid (DA), produced by toxic species of Pseudo-nitzschia was found with concentrations up to 18 µg DA g −1 in the smooth clam Callista chione. Data showed that the observed persistent and dramatic Paralytic Shellfish Poisoning (PSP) intoxication of mollusks resulted probably of Gymnodinium catenatum pro-liferations in both studied areas. Contrary to C. chione, the cockle Achanthocardia tuberculatum showed a permanent and extremely high toxicity level during the 15 months survey with up to 7545 µg Equivalent Saxitoxin kg −1 flesh (ten times higher than the sanitary threshold of 800 µg eqSTX Kg −1 flesh). The present work highlights for the first time the dynamic of microphytoplankton including HABs species and their associated toxin accumulation in the commercially exploited shellfish in the southern western Mediterranean waters of Morocco. Furthermore, the acquired data will help us to improve the monitoring of HABs species and related toxins in these coastal marine systems.

Mots clés: Environmental factors; Phytoplankton diversity; SW Mediterranean; Toxins; HABs

Domaines: Biodiversité et Ecologie; Interactions entre organismes; Ecosystèmes; Océanographie

Benlahcen Rijal Leblad, Rachid Amnhir, Sagou Reqia, Ferdaous Sitel, Mouna Daoudi, et al.. Seasonal variations of phytoplankton assemblages in relation to environmental factors in Mediterranean coastal waters of Morocco, a focus on HABs species. Harmful Algae, 2020, 96, pp.101819. ⟨10.1016/j.hal.2020.101819⟩. ⟨hal-02863649⟩