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Few works have been carried out on benthic harmful algal blooms (BHAB) species in the southern Mediterranean and no data are available for the highly dynamic Strait of Gibraltar (western Mediterranean waters). For the first time, Ostreopsis sp. 9, Prorocentrum lima and Coolia monotis were isolated in this key region in terms of exchanges between the Atlantic Ocean and the Mediterranean and subject to intense maritime traffic. Ribotyping confirmed the morphological identification of these three dinoflagellates species. Monoclonal cultures were established and the maximum growth rate and cell yield were measured at a temperature of 24 °C and an irradiance of 90 µmol photons m−2 s−1, for each species: 0.26 ± 0.02 d−1 (8.75 × 103 cell mL−1 after 28 days) for Ostreopsis sp. 9, 0.21 ± 0.01 d−1 (49 × 103 cell mL−1 after 145 days) for P. lima and 0.21 ± 0.01 d−1 (10.02 × 103 cell mL−1 after 28 days) for C. monotis. Only P. lima was toxic with concentrations of okadaic acid and dinophysistoxin-1 measured in optimal growth conditions ranging from 6.4 pg cell−1 to 26.97 pg cell−1 and from 5.19 to 25.27 pg cell−1, respectively. The toxin content of this species varied in function of the growth phase. Temperature influenced the growth and toxin content of P. lima. Results suggest that future warming of Mediterranean coastal waters may lead to higher growth rates and to increases in cellular toxin levels in P. lima. Nitrate and ammonia affected the toxin content of P. lima but no clear trend was noted. In further studies, we have to isolate other BHAB species and strains from Strait of Gibraltar waters to obtain more insight into their diversity and toxicity.

The southern Alboran Sea is a dynamic ecosystem and is highly influenced by Atlantic waters. Unfortunately, despite the importance of the mesozooplankton in this ecosystem, the number of studies on this ecosystem is low. The composition and abundance of mesozooplankton communities were studied during the summer season (July 2017) along the Moroccan Mediterranean coast between M’diq and Saïdia. A total of 14 mesozooplankton groups were identified and were dominated by copepods (48%) and cladocerans (35%). Abundance and biomass spatial distribution distinguished two main regions east and west of Al Hoceima. The same distribution pattern was observed when using copepod and cladoceran abundance. Environmental parameters (temperature, salinity, and nutrients) differed in these two regions. Our results confirm the hypothesis that the water flux from the Atlantic Ocean is responsible for the eastward gradients of the mesozooplankton abundance and diversity. Copepods were the most diversified group with 27 species, dominated by Paracalanus parvus (30.5%), Temora stylifera (14%), and Oncaea venusta (12.4%). The diversity index (H’) of copepods varied between 1.35 and 2.8 bits ind−1, and the regularity index (J) varied between 0.21 and 0.45, without a remarkable longitudinal gradient. Multivariate analysis showed that the mesozooplankton biomass, abundance, and distribution were influenced mainly by hydrology (gyres), by temperature and salinity, and to a lesser degree by phytoplankton.

Vulcanodinium rugosum is an emerging benthopelagic neuro-toxic dinoflagellate species responsible for seasonal Pinnatoxins and Portimines contaminations of shellfish and marine animals. This species is challenging to detect in the environment, as it is present in low abundance and difficult to be identified using light microscopy. In this work, we developed a method using artificial substrates coupled with qPCR (AS-qPCR) to detect V. rugosum in a marine environment. This sensitive, specific and easy-to-standardize alternative to current techniques does not require specialized expertise in taxonomy. After determining the limits and specificity of the qPCR, we searched for the presence of V. rugosum in four French Mediterranean lagoons using artificial substrates collected every two weeks for one year. The AS-qPCR method revealed its occurrences in summer 2021 in every studied lagoon and detected cells in more samples than light microscopy. As V. rugosum development induces shellfish contamination even at low microalga densities, the AS-qPCR method is accurate and relevant for monitoring V. rugosum in a marine environment.

Le projet SECTOX porte sur l’étude de la contamination par les phycotoxines (PST et lipophiles dont DST) des huîtres creuses et des moules de la lagune de Thau ainsi que la dynamique temporelle et spatiale de cette contamination dans l’optique d’une gestion sectorisée de la lagune. Les campagnes de terrain ont été réalisées entre septembre 2019 et décembre 2020.La contamination des toxines lipophiles et des toxines hydrophiles (PST) a été suivie dans plusieurs matrices : coquillages et échantillonneurs passifs. Le suivi des espèces toxiques dans la colonne d’eau a été opéré selon plusieurs méthodes d’analyses et techniques d’échantillonnage. L’étude a mis en évidence que la contamination par les toxines lipophiles produites par une microalgue appartenant au genre toxique Dinophysis, impacte l’ensemble de la lagune de Thau sans qu’il soit possible de déterminer des dynamiques différentes entre les différents secteurs de la lagune. L’absence de prolifération du dinoflagellé Alexandrium pacificum (producteur de PST) sur la période suivie n’a pas permis de conclure sur l’existence d’une dynamique spatio-temporelle différente entre les secteurs de l’étang de Thau pour le risque de contamination par les PST. L’étude a aussi permis de tester de nouveaux outils (SPATT, échantillonneur passif pour les toxines) ainsi que la méthode de qPCR utilisant les outils de la biologie moléculaire pour l’identification et le dénombrement des espèces toxiques. Les résultats obtenus montrent que ces techniques sont prometteuses mais nécessitent une optimisation avant une utilisation en « routine » dans le volet sanitaire du réseau de surveillance REPHY.

Pinnatoxins (PnTX) and Portimines (Prtn), two toxins produced by the benthic dinoflagellate Vulcanodinium rugosum, are known to be lethal to mice after intraperitoneal or oral administration. They are also known to accumulate in shellfish such as mussels and clams, but their effect on fish and the upper food chain remains unknown. In this work, juveniles of the fish Liza ramada (Mullet) were exposed to a strain of V. rugosum producing PnTX G and Prtn A. The fishes’ viability and contamination were recorded at times interval. Results showed that L. ramada juveniles were able to feed on V. rugosum and that their tissues could be contaminated by PnTX G and Prtn A without impact on fish viability. Furthermore, the microalgae temporary cysts survived and germinated after fish gut passage. This study showed the potential of L. ramada to transfer PnTX and Prtn toxins to the upper food chain and to disseminate V. rugosum in environment.

The southern Alboran Sea is a highly dynamic region in the Mediterranean. However, there is few data on microphytoplankton which is, an important component of the marine ecosystem. We, therefore, collected microphytoplankton samples and related the biomass and diversity patterns to ambient variability, considering cross-shore and longitudinal gradients. There was a general eastward decrease in both species richness and biomass, with Cape Three Forks as a transitional point. Diversity increased in coastal areas and decreased with depth. High chlorophyll-a concentrations corresponded to low temperature and low-salinity waters, indicating the Atlantic origin. Microphytoplankton biomass was low in comparison with total chlorophyll, suggesting a dominance of nano- and picophytoplankton. Biomass values increased in the stretch between Cape Three Forks and Al Hoceima Bay, an area highly influenced by upwelled water originating from the northern Alboran Sea. We suggest that the Western Alboran Gyre enhances the development of dinoflagellates while local upwelling enhances the development of diatoms. A statistical relationship was found between microphytoplankton biomass and diversity, especially when diversity was estimated as species richness. These results are crucial for understanding microphytoplankton dynamics and trends in an area that is undergoing climate-derived changes and biodiversity losses.

The southern Alboran Sea is a highly dynamic region in the Mediterranean. However, there is few data on microphytoplankton which is, an important component of the marine ecosystem. We, therefore, collected microphytoplankton samples and related the biomass and diversity patterns to ambient variability, considering cross-shore and longitudinal gradients. There was a general eastward decrease in both species richness and biomass, with Cape Three Forks as a transitional point. Diversity increased in coastal areas and decreased with depth. High chlorophyll-a concentrations corresponded to low temperature and low-salinity waters, indicating the Atlantic origin. Microphytoplankton biomass was low in comparison with total chlorophyll, suggesting a dominance of nano- and picophytoplankton. Biomass values increased in the stretch between Cape Three Forks and Al Hoceima Bay, an area highly influenced by upwelled water originating from the northern Alboran Sea. We suggest that the Western Alboran Gyre enhances the development of dinoflagellates while local upwelling enhances the development of diatoms. A statistical relationship was found between microphytoplankton biomass and diversity, especially when diversity was estimated as species richness. These results are crucial for understanding microphytoplankton dynamics and trends in an area that is undergoing climate-derived changes and biodiversity losses