Pseudo-nitzschia Peragallo (Bacillariophyceae) diversity and domoic acid accumulation in tuberculate cockles and sweet clams in M’diq Bay, Morocco

The diversity of Pseudo-nitzschia (Bacillariophyceae) and accumulation of the neurotoxin domoic acid (DA) in two types of shellfish; tuberculate cockles (Acanthocardia tuberculata) and sweet clams (Challista chione) was explored in M’diq Bay,Morocco during 2007. The highest abundances of Pseudo-nitzschia were found during the period from March to October, with peaks occurring in May and September. Toxin analysis showed an accumulation of domoic acid in shellfish sampled during spring and autumn. The maximum toxin concentration was 4.9 mg DAg–1 of the whole tissue recorded in sweet clam during spring. Using transmission electron microscopy, thirteen Pseudo-nitzschia species were identified, eight of which are known as producers of domoic acid: P. multistriata, P. cuspidata, P. galaxiae, P. multiseries, P. pseudodelicatissima, P. pungens var. aveirensis, P. calliantha and P. fraudulenta. The five non- toxic species observed were P. subpacifica, P. arenysensis, P. dolorosa, P. subfraudulenta, and P. cf. caciantha

Pseudo-nitzschia Peragallo (Bacillariophyceae) diversity and domoic acid accumulation in tuberculate cockles and sweet clams in M'diq Bay, Morocco

International audienceThe diversity of Pseudo-nitzschia (Bacillariophyceae) and accumulation of the neurotoxin domoic acid (DA) in two types of shellfish; tuberculate cockles (Acanthocardia tuberculata) and sweet clams (Challista chione) was explored in M'diq Bay, Morocco during 2007. The highest abundances of Pseudo-nitzschia were found during the period from March to October, with peaks occurring in May and September. Toxin analysis showed an accumulation of domoic acid in shellfish sampled during spring and autumn. The maximum toxin concentration was 4.9 mg DA g-1 of the whole tissue recorded in sweet clam during spring. Using transmission electron microscopy, thirteen Pseudo-nitzschia species were identified, eight of which are known as producers of domoic acid: P. multistriata, P. cuspidata, P. galaxiae, P. multiseries, P. pseudodelicatissima, P. pungens var. aveirensis, P. calliantha and P. fraudulenta. The five non-toxic species observed were P. subpacifica, P. arenysensis, P. dolorosa, P. subfraudulenta, and P. cf. caciantha

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

International audienceStudies 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

New insights into the dynamics of causative dinoflagellates and the related contamination of molluscs by paralytic toxins in the southwestern Mediterranean coastal waters of Morocco

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Occurrence of three dominant epibenthic dinoflagellates (Ostreopsis spp., Coolia monotis and Prorocentrum lima) in relation to biotic substrates and environmental factors in a highly dynamic ecosystem, the Strait of Gibraltar (Southwestern Mediterranean)

No studies have been carried out on the benthic harmful algal blooms (BHABs) along the Strait of Gibraltar in the Mediterranean, and little is known about the diversity of blooming species. Here, epibenthic dinoflagellates were monitored at least biweekly over 18 months (May 2019–November 2020) in Oued Lihoud, Cap Malabata and Dalia on the thalli of five dominant macrophytes and in the water column. This is the first report on the seasonal distribution of BHAB species hosted by natural biotic substrates in the Strait of Gibraltar, which is known for high hydrodynamics, major entry of Atlantic waters and important maritime traffic. Three BHAB dinoflagellates were observed in the surveyed areas: Ostreopsis spp., Coolia monotis and Prorocentrum lima. The analysis of all data at the three sites showed that Dictyota dichotoma was the most favourable macroalgae host for these benthic dinoflagellates. The highest cell densities were observed in Cap Malabata for Ostreopsis spp. (2.7 × 105 cells/g fresh weight in September 2020), P. lima (4.57 × 104 cells/g FW in September 2020) and C. monotis (4.07 × 104 cells/g FW in June 2019). Phosphate and temperature were positively correlated to the abundances of the studied thermophilic BHAB species. In contrast, negative correlations were recorded with salinity, ammonium, nitrite, nitrate, DIN, nitrogen/phosphate ratio and suspended material, attesting of the complex relationships between environmental factors and BHAB species dynamic in each marine ecosystem. Toxin analyses of the natural phytoplankton assemblage during BHABs showed the presence of only lipophilic toxins, namely okadaic acid and dinophysistoxins produced by P. lima. These BHABs species have to be isolated to establish monoclonal cultures for ribotyping and ecophysiological investigations

Development of harmful algal blooms species responsible for lipophilic and amnesic shellfish poisoning intoxications in southwestern Mediterranean coastal waters

Mediterranean waters have undergone environmental changes during the last decades leading to various modifications of the structure of phytoplankton populations, especially Harmful Algal Blooms (HABs) species. Monitoring of the potentially toxic phytoplankton species was carried out biweekly in the western Mediterranean coast of Morocco from March 2018 to March 2019. Lipophilic Shellfish Toxins (LSTs) using LC-MS/MS and Domoic Acid (DA) using HPLC-UV were measured in the exploited mollusks, the cockle Acanthocardia tuberculata and the smooth clam Callista chione. We also determined the prevailing environmental factors in four surveyed sites (M'diq bay, Martil, Kaa Asras, and Djawn) selected to cover a variety of coastal ecosystems. Results showed that Pseudo-nitzschia spp. A DA producer species, was abundant with a pick of 50 × 103 cells l−1 on October 2018 in Djawn. Dinophysis caudata was the dominate Dinophysis species and showed a maximum density of 2200 cells l−1 on July in Djawn. Prorocentrum lima, an epibenthic dinoflagellate, appeared rarely in the water column with densities <80 cells l−1. Gonyaulax spinifera and Protoceratium reticulatum were found occasionally with a maximum density of 160 cells l−1. Karenia selliformis was detected only five times (<80 cells l−1) throughout the survey period. LC-MS/MS analyses revealed the presence of OA/DTX3, PTX-2, PTX-2 sa, and PTX-2 sa epi in the cockle at concentrations of up to 44.81 (OA/DTX-3+PTXs) ng g−1 meat. GYM-A was detected in the clam at concentrations of up to 4.22 ng g−1 meat. For the first time, AZAs and YTXs were detected in the southwestern Mediterranean with maximum values of 2.49 and 10.93 ng g−1 meat of cockle, respectively. DA was detected in moderate concentrations not exceeding 5.65 μg g−1 in both mollusks. Results showed that the observed toxic algae in the water column were responsible from the analysed toxins in the mollusks. It is likely that the southwestern Mediterranean waters could see the development of emergent species producing potent toxins (YTXs, AZAs, GYM-A). These dinoflagellates have to be isolated, ribotyped, and their toxin profiles determined

Potential to produce brown mussel integrated to a net-cage fish farm in a Mediterranean bay

In this study, we investigated the potential exploitation of the brown mussel Perna perna (Linnaeus, 1758) in an aquaculture farm (Monastir Bay, Mediterranean Sea, Tunisia). The quality of seawater as well as performance indicators such as Condition Index, length, weight, growth and frequency distribution of the mussel were determined over an annual cycle; from July 2017 to August 2018. Interestingly, P. perna has an extended sexual cycle during the year with two main spawning periods, the first in spring and the second in autumn, when suspended matter and Chlorophyll a were at their maximum concentrations in seawater. Spat mussels and young mussels showed significant growth rates from 1 July 2017 to 31 October 2017. Adult mussels exhibited negative allometric growth and a modal size of 41 to 50 mm. Results showed that several potentially toxic microalgae species developed at low densities in this marine zone. By using Solid Phase Adsorption Toxins Tracker (SPATT); lipophilic toxins including Okadaic acid and yessotoxins were detected at low levels in seawater and may be involved in the positive LSTs (lipophilic shellfish toxins) mouse bioassays in P. perna during the autumn. No other toxins such as paralytic shellfish toxins or amnesic shellfish toxins nor pathogenic bacteria or viruses were detected in P. perna. Altogether, our results suggest that finfish farms in Monastir Bay could be suitable sites for farming P. perna