Variations de la structure trophique du lac-réservoir oligotrophe Bin El Ouidane (Maroc)

L'étude combinée des apports par les crues, du plancton, des contenus algaux du tractus digestif des Cladocères et du régime alimentaire de quelques espèces de poissons dans le lac de barrage oligotrophe Bin El Ouidane a permis de dégager les conclusions suivantes :- les apports particulaires et dissous par les crues durant la période d'étude 1995-1997 ont une influence marquée sur la dynamique saisonnière du zooplancton via les changements dans la dynamique du peuplement phytoplanctonique ;- durant les trois années d'étude, le maximum de biomasse zooplanctonique se situe généralement juste après les pics printanier et estival du phytoplancton mettant ainsi en évidence l'importance du zooplancton herbivore dans la chaîne alimentaire pélagique du lac ;- l'étude des contenus algaux du tractus digestif des Cladocères Daphnia longispina, Daphnia lumholtzi, Diaphanosoma brachyurum, Ceriodaphnia dubia, Ceriodaphnia reticulata et Bosmina longirostris a montré que l'essentiel des espèces sont des filtreuses herbivores qui adoptent un comportement nutritionnel variable en fonction du temps lié à la disponibilité en phytoplancton, à leur âge et aux caractéristiques biotiques et abiotiques de l'écosystème lacustre ; - l'étude préliminaire du régime alimentaire de trois espèces de poissons Tinca tinca, Eupomotis gibbosus et Cyprinus carpio montre que leur spectre alimentaire est nettement dominé par le plancton. La fraction faunistique au niveau de leur tube digestif est représentée essentiellement par les Cladocères de grande taille et les Chironomes. Ceci met en évidence l'importance de ces poissons, à régime essentiellement planctonophage, dans la régulation des peuplements planctoniques de la retenue Bin El Ouidane.The study of the flood transport, plankton and the stomach contents of Cladoceran species and some planktivorous and omnivorous fish of the reservoir-lake Bin El Ouidane has allowed to extract the following conclusions:- flood transport of dissolved and suspended matters during the period 1995-1997 has a net influence on the seasonal dynamics of the zooplancton via changes in the dynamics of the phytoplanktonic populations;- during the same period, the peak of zooplanktonic biomass appeared generally just after spring and summer phytoplanktonic peaks showing the importance of the herbivorous zooplankton in the food chain;- the study of algal stomach contents of Cladocerans Daphnia longispina, Daphnia lumholtzi, Diaphanosoma brachyurum, Ceriodaphnia dubia, Ceriodaphnia reticulata and Bosmina longirostris showed that all species are herbivorous filter-feeders that adopt a variable diet behavior linked to the availability of the phytoplankton in the lake, to their age and biotic and abiotic characteristics of the ecosystem;- the preliminary study of the stomach contents of three omnivorous and herbivorous fish Tinca tinca, Eupomotis gibbosus and Cyprinus carpio species showed also that their food spectre was clearly dominated by the plankton. The animal fraction in their digestive tube was represented by large Cladoceran species and Chironomes showing the importance of these fish, essentially planktivorous, in the regulation of planktonic populations in the reservoir-lake Bin El Ouidane

Croissance en autotrophie et en mixotrophie de la microalgue Micractinium pusillum Fres. isolée d´un lagunage naturel : influence de la lumière et de la température

Dans le but d'étudier la dynamique des microalgues dans le lagunage naturel de Ouarzazate (sud du Maroc) et éventuellement sa modélisation, nous avons eu recours à la détermination des paramètres de croissance (µmax, Iopt et b) selon le modèle de PEETERS et EILERS (1978). À cet effet, Micractinium pusillum, algue verte Chlorococcale se développant dans les bassins de lagunage de la station pilote de Ouarzazate, a été isolée et mise en culture sur milieu synthétique (DAUTA, 1982) enrichi en azote et en phosphore sous des conditions contrôlées de lumière et de température.En autotrophie, l'application du modèle de PEETERS et EILERS (1978) à la croissance de Micractinium pusillum, a permis la détermination des paramètres : µmax (0,58 j-1), I opt (182 µE·m-z·s-1) et b (0,1) à la température maximale de croissance de 35 °C. En mixotrophie et à la même température, ces paramètres sont respectivement de 0,85 j-1, 150 µE·m-z ·s-1 et 1. Comparativement à la croissance en autotrophie, la croissance de Micractinium pusillum en mixotrophie, en présence d'acétate, a mis en évidence la variation, selon le régime trophique de l'algue, des paramètres de croissance µmax, Iopt et b. La croissance en mixotrophie, comportement probable dans le lagunage naturel, a conduit particulièrement à l'élévation du taux de croissance et du coefficient b. La variation du coefficient b traduirait une certaine sténophotie de la microalgue en autotrophie et une tendance à l'euryphotie en mixotrophie. Cette étude a montré également que l'influence de l'intensité lumineuse sur la croissance varie en fonction du mode trophique.In the wastewater stabilization pond, the growth of the microalgae depends on several factors such as temperature, light and nutriments. In addition to these factors, the presence of the organic matter has great influence on the development in such system. In the aim to study the dynamic of the microalgae in the wastewater stabilization pond of Ouarzazate city (south of Morocco) and possibly its modelling, the determination of the growth parameters (µmax, Iopt and b) has been carried out according to the model of PEETERS and EILERS (1978). Indeed, Micractinium pusillum, a Chlorococcal green algae developing in the experimental wastewater stabilization pond of Ouarzazate city has been isolated and cultured under controlled conditions of light and temperature on synthetic medium (DAUTA, 1982) enriched in nitrogen and phosphorus.In autotrophic conditions, application of the PEETERS and EILERS model to the growth of Micractinium pusillum, resulted in the determination of the parameters: µmax (0,58 day-1), Iopt (182 µE·m-z·s-1) and b (0,1) using the maximal growth temperature of 35°C. In mixotrophic conditions under the same temperature, these parameters were respectively 0,85 day-1, 150 µE·m-z ·s-1 and 1. According to the trophic mode, the growth of Micractinium pusillum revealed a variation of the parameters µmax, Iopt and b. The mixotrophic growth, probable behaviour in the wastewater stabilization pond, has induced particularly the elevation of the growth rate and the coefficient b. Also, this study showed that light intensity has varied effects on the growth of microalgae in the two trophic modes

Variabilité des descripteurs physiques, chimiques et phytoplanctonique dans des étangs d'alevinage (station de la Deroua, Béni-Mellal, Maroc)

Dans les étangs d'alevinage à la station de la Deroua, le phytoplancton est représenté par des populations se succédant dans le temps.Ces étangs montrent une similarité vis-à-vis de la variabilité des descripteurs de la qualité de l'eau. Les résultats statistiques montrent une variabilité des paramètres physiques et chimiques dépendant des interventions anthropiques.Les deux étangs B3 et B4 présentent des groupements phytoplanctoniques plus importants avec un développement de Cyanobactéries en fin du cycle d'alevinage lié à une forte biodisponibilité du phosphore dissous.In fry ponds at Deroua farm, the phytoplankton was represented by a temporal succession of taxa groups.This study showed a similar variability of physical and chemical parameters in fishponds. The statistical analysis proved a variability of these parameters depending of human interventions.At the end of fry period, the phosphorus concentration in B3 and B4 ponds allowed a development of Cyanobacteri

Relargage du phosphore à l'interface eau-sédiment dans des étangs de pisciculture de la station Deroua (Béni Mellal, Maroc)

De l'urée et du super phosphate triple ont été appliqués aux étangs d'alevinage de carpes chinoises de la station Deroua pour stimuler la croissance des algues. Toutefois, une forte proportion de ce phosphore est fixée par les sédiments et sera libérée en grande quantité dans les étangs lorsque les sédiments sont en conditions anaérobies.Nous avons étudié le relargage des orthophosphates par les sédiments provenant de deux étangs différents. L'un (A1) en terre ce qui permet la percolation des éléments nutritifs vers les couches profondes, l'autre (C1) dont le fond recouvert d'une fine membrane en polyéthylène, est parfaitement imperméable et empêche toute perte. Par ailleurs, nous avons étudié les effets de l'oxygène dissous, du pH, des nitrates et du glucose sur le relargage des orthophosphates par les sédiments.Les résultats obtenus montrent qu'en anaérobiose, la solubilité du phosphore augmente dans l'eau interstitielle. Les orthophosphates libérés, dont la concentration peut atteindre 873 µg/l, proviennent de la fraction minérale en particulier du Fe(OOH)=P. Le sédiment C1 qui accumule de grandes quantités de matière organique libère plus de phosphore que le sédiment A1.L'addition des nitrates limite la mobilisation du phosphore à partir des sédiments. Le pH acide provoque la dissolution du phosphore lié au calcium alors qu'un pH alcalin provoque celle du phosphore lié aux hydroxydes de fer et sa précipitation partielle sur les carbonates présents dans les sédiments.In the Deroua fish farm (Béni-Mellal, Morocco), a series of ponds was lined with polyethylene to prevent water seepage (lined ponds, C). Another series of ponds was not lined (unlined ponds, A). The lined ponds do not need much fertiliser to enhance phytoplankton growth. They receive a small quantity of urea and triple super phosphate and accumulate high levels of organic matter in their sediments. The unlined ponds receive a large quantity of fertilisers. In the ponds, an important increase in phytoplankton growth occurred particularly after fertilisation with triple super phosphate. The phosphate (P) released from the sediment is the essential source of P for phytoplankton when the ponds are not fertilised.Sediment samples used in this study were collected in June 1999 from the A1 and C1 ponds of the Deroua fish farm. The bottom sediments were collected with a core sampler to provide samples from the 0-5 cm layer. The samples were mixed and analysed for pH, total Kjeldahl nitrogen (NTK), nitrates (N-NO3-), ammonium (N-NH4+), total iron (tot-Fe) and P-fractionation in eight replicates, using the Golterman method (1996).In this work, experiments were conducted to evaluate the P released from sediments of lined and unlined ponds under controlled conditions. The samples included: untreated sediments, sediments treated with hydrogen peroxide (H2O2), and sediments treated with chloroform (CHCl3). H2O2 was used to destroy the organic matter of sediment. To inactivate bacteria, CHCl3 was added to the sediments. CHCl3 does not modify the mineral and organic structures of sediments but does reduce the bacterial biomass. Urea and triple super phosphate were added to Chinese carp rearing ponds at Deroua fisheries farm to stimulate algal growth. However, phosphate bound to the sediments was released into the water column during anaerobic conditions. The released phosphate from lined pond (C1) enhanced the algal production.We have tested the fertilisation capacity of A1 and C1 ponds as well as the effects of different factors such as dissolved oxygen, pH, nitrate, and organic matter (glucose) on the phosphate released from the sediments. The results show that under anoxic conditions, phosphate solubility increased in the interstitial water. The released phosphate (873 µg/l) comes from the mineral fraction, particularly from Fe(OOH)=P. The P released from the A1 untreated sediment under oxic and anoxic conditions was low in comparison to the P released from the C1 untreated sediment and did not exceed 9.1 µg.g-1 d.w. (Figure 1). The removal of organic matter with H2O2 had a positive effect on the P released from the C1 sediments only after the second day of incubation. The inactivation of bacteria with CHCl3 had an inhibitory effect on the P released from the C1 sediments under oxic and anoxic conditions; however for the A1 sediments, this inactivation of bacteria had no effect on the kinetics of P release. Phosphorus release from the C1 sediments was important under anoxic conditions; the P came from Fe(OOH)=P after the reduction of Fe(OOH).The addition of nitrates decreased the mobilisation of phosphate from the sediments. Acid conditions increased the dissolution of calcium-bound phosphate, while alkaline conditions increased the dissolution of iron-bound phosphate and its re-precipitation onto carbonate present in sediments. High concentrations of organic matter (glucose) increased oxygen demand and favoured the development of reducing conditions. The phosphate was released from Fe(OOH)=P.The conceptual model of P released in fish ponds shows that, in semiarid climates and in calcareous areas, the polyethylene lining of ponds prevents not only the seepage of water but also the percolation of nutrients. Consequently, the P was more available for algal uptake in the lined ponds. More phosphate will be released concomitant with the process of the ponds becoming anoxic, as nitrate concentrations and the pH of sediments decrease

Étude des blooms toxiques à cyanobactéries dans trois lacs réservoirs du Maroc : résultats préliminaires

Dans le cadre du programme de recherche sur les blooms toxiques à cyanobactéries dans certains lacs de barrage du Maroc, une étude de ce phénomène a été entreprise sur trois retenues : Lalla Takerkoust, Oued Mellah et Al Massira. L'étude taxonomique montre que dans les lacs Lalla Takerkoust et Al Massirra, l'espèce responsable des blooms est Microcystis aeruginosa alors que dans la retenue saumâtre et hypereutrophe Oued Mellah, c'est Microcystis ichthyoblabe.En complément, une étude toxicologique et toxinologique a permis d'évaluer les risques sanitaires potentiels qui peuvent être engendrés par ces blooms. L'hépatotoxicité, pour l'ensemble des blooms récoltés en 1999, a été confirmée par le biotest " souris ". L'application de ce test a montré que le bloom de LallaTakerkoust est hautement toxique (DL50 500 mg/kg) et celui d'Al Massira est intermédiaire (DL50 comprise entre 100 et 500 mg/kg). Les teneurs en microcystines (hépatotoxines) déterminées par ELISA révèlent des concentrations beaucoup plus importantes pour le bloom de Lalla Takerkoust. L'utilisation de la chromatographie liquide haute performance avec détecteur à barrette photodiode, (CLHP-DBP) a permis la détection et l'identification de 2, 4 et 11 variantes de microcystines, respectivement à partir d'extraits du bloom naturel d'Al Massira, Lalla Takerkoust et Oued Mellah. Cependant, la Microcystine-LR n'a été détectée que dans les extraits d'Al Massira et de Takerkoust. L'apparition des blooms toxiques à cyanobactéries dans ces plans d'eau impose dorénavant la prise en considération des nuisances écologiques et des risques sanitaires liés à la présence des microcystines dans ces eaux.During the first part of the toxic cyanobacteria survey program carried out since 1994, Microcystis blooms which periodically occurred in Al Massira, Lalla Takerkoust and Oued Mellah reservoirs were studied. These reservoirs were located at a different hydrographic basin and have a various trophic status. The water was used for irrigation, recreational purpose and/or drinking water supply. The bloom-forming species was identified as Microcystis aeruginosa in Al Massira and Takerkoust freshwater reservoirs whereas in brackish water Oued Mellah reservoir, the bloom-forming species is Microcystis ichthyoblabe.In complement to this ecological studies and in order to assess the potential health risk, a toxicology and toxinology of these Microcystis blooms were undertaken. The hepatotoxicity of lyophilized bloom material collected during bloom periods in 1999 was confirmed by (i. p) mice bioassay. The toxicity assessment revealed that Microcystis Takerkoust bloom was highly toxic with LD50 < 100 mg/kg whereas those from Al Massira and Oued Mellah were respectively characterized by a medium and a low toxicities.The content of microcystins (MCYST) determined by the Enzyme-linked Immunosorbent assay (ELISA) show that MCYST content ranged between 0.37 to 496 µg/g dry weight. It appears that Takerkoust bloom contain 600 to 1300 fold more MCYST than Oued Mellah and Al Massira blooms. The isolation and identification of microcystins variants from bloom extracts were performed using the high performance liquid chromatography with photodiode array detection (HPLC-PDA). This technique provided the separation and identification of at least two microcytins variants from each bloom material. The most number of 11 microcystins were detected from Microcystis ichthyoblabe bloom of Oued Mellah. However, only two and four variants of microcystins were respectively detected from Al Massira and Takerkoust blooms. Among these variants of microcystins solely Microcystin-LR was identified according to the Mcyst-LR authentic sample from extract of Al Massira and Takerkoust blooms.The occurrence of toxic cyanobacteria bloom in these drinking and/or recreational water reservoirs lead us to take into consideration the real health hazard which will be induced by these harmful cyanobacterial blooms

Application de certains indices diatomiques à un cours d'eau marocain : Oued Hassar

Les eaux de l'Oued Hassar (Maroc) sont caractérisées par une forte minéralisation. La conductivité, variant entre 3470 et 7210 µS.cm-1, est due essentiellement aux fortes teneurs en chlorures. L'examen de l'Indice de Pollution Organique (IPO) montre que l'effluent d'eaux usées provenant de la ville de Mediouna constitue la principale source de pollution des eaux de l'Oued Hassar.Concernant l'étude des diatomées épilithiques, 61 espèces et variétés de diatomées ont été inventoriées. Ces taxons sont liés particulièrement à la salinité (Pleurosira laevis, Fragilaria pulchella,…) et à la charge organique (Nitzschia palea, Gomphonema parvulum,…).Quatre indices diatomiques ont été testés pour l'évaluation de la qualité des eaux de l'Oued Hassar : l'Indice Diatomique Pratique (IDP), l'Indice Diatomique Générique (IDG), l'Indice de Sládecek (SLA) et l'Indice Diatomique Trophique (IDT). La variation spatio-temporelle de ces indices reflète bien la dégradation de la qualité de ce cours d'eau, particulièrement en aval du rejet de la ville de Mediouna (IDP=3,86 ± 1,84 ; IDG=6,05 ± 1,95 ; SLA=4,35 ± 1,93 ; IDT=5,80 ± 1,31). Parmi ces indices testés, seul l'IDP présente une corrélation significative (0,63 ; α<5%) avec l'IPO (indice de référence) tandis que l'IDG, le SLA et l'IDT montrent des corrélations non significatives avec cet indice (0,38 ; 0,27 et -0,11 respectivement).The water quality in Moroccan rivers and streams becomes more and more injured because of the important amount of pollutants discharged in these aquatic ecosystems without any treatment in the most cases. A physical, chemical and microbiological analyses are regularly done by public institutions (office national des eaux potables, direction de l'hydrolique). However, these analyses become insufficient facing the big diversity of chemicals and the intermittence of pollution sources at the time. So, methods using a biotic indicators as a complement of the chemical analyses become a requirement in the water quality assessment. In the present study, besides the physical and chemical analyses, we have tested the use of benthic diatoms as indicators of the oued Hassar water quality and diatom indices as a tool for the evaluation of this quality.Oued Hassar is a canalized stream situated on the valley of oued Mellah river. It drains a part of the Berrechid groundwater as sources. Its main source (station SC) is situated to 3 km in the Northeast of Mediouna (155 m). Along this water course, in sections of various degrees of water pollution, six sites (SC, SB, HP, OM, SH and CA) were sampled on four different dates (august 1997 and january, june and august 1998). The station OM belongs to oued Mouileh stream which is a unique tributary of oued Hassar. The main source of pollution; the wastewater effluent of Médiouna agglomeration entered the stream between The oued Hassar source and the station SB (Sidi Brahim). This region has a Mediterranean semi-aride bioclimate. The influence of the ocean results in a summer temperatures generally varying between 25 and 30°C and winter temperatures varying between 12 and 19°C.The physical and chemical analysis data of the oued Hassar waters show particularly elevated values of water conductivity essentially due to the high contents in chlorides. These values were understood between a minimal value recorded at station SH in August 1998 (3470 mS.cm-1) and a maximal value signalled at station OM in January of the same year (7210 mS.cm-1). Concentrations in sulphates vary according to stations. The most elevated values were recorded in january 1998 at stations SC and OM (231 and 218 mg.l-1 respectively). The hardness values are very important especially at the source of oued Hassar (SC) where the concentration reaches 25,2 meq.l-1. This excessive mineralization of waters, particularly at stations SC and OM, is essentially due to the Permo-triasique saliferous sedimentary layers which crop out in the area.The oued Hassar stream receives, to 100 ms downstream the station SC, the wastewater effluent of Médiouna agglomeration, highly loaded with organic matters, ammonia, orthophosphates and suspended matters. The impact of this effluent results on the elevated values of these parameters downstream the wastewater input (SB). On January 1998 (rainy period), the important contents in orthophosphates and sulphates recorded at all stations were essentially due to the high amounts of superphosphates and ammonia sulphates used as amendment of the cultivated lands situated a long the sides of oued Hassar stream.Outside of this period, contents in orthophosphates and ammonia at stations SC and OM are very low. However, the elevated content in nitrates at the oued Hassar's source (maximal value: 93,3 mg.l-1) gives an idea on the deterioration of the groundwater quality.To put in evidence the evolution of the global organic pollution of waters, the "Indice de Pollution Organique" (IPO) have been calculated. The exam of this index shows that the wastewater effluent constitutes the main source of pollution. Indeed, water quality goes from a mean pollution state (3,88 ± 0,14) at the oued Hassar's source to a very strong pollution state (1,96 ± 0,31) at the station SB. Downstream the swampy zone, at the station HP, the water quality of oued Hassar improves remarkably (3,50 ± 0,74) due to the auto-purification phenomenon and the dilution of these waters by those coming from the secondary sources situated between stations SB and HP. At the stations SH and CA, the IPO mean values (3,50 ± 0,79 and 3,75 ± 0,41 respectively) show that the water quality remains rather identical as at the station HP.Concerning the survey of epilithic diatoms, 61 species and varieties of diatoms have been inventoried. These taxa are bound especially to the salinity (Amphora coffeaeformis, Fragilaria fasciculata, Fragilaria pulchella, Pleurosira laevis,…) and to the organic load (Gomphonema parvulum, Navicula subminuscula, Nitzschia palea,…). In the most collected samples, particularly at the stations SB, SH and CA, diatom communities are essentially dominated by N. palea and the complex N. inconspicua / N. frustulum. At the station SB, the relative abundance of N. palea reaches 71% in august 1997 and august 1998, and goes beyond 45% in January and june 1998. giving evidence of the important organic pollution. this species is substituted, at stations SH and CA, essentially by Navicula subminuscula, N. veneta and Nitzschia inconspicua / N. frustulum complex. Diatom communities at the stations SC, HP and OM don't show an exclusive dominance of one or two species, but several species dominate and form a more varied communities.Four diatom indices have been tested to assess the water quality in Oued Hassar (Morocco) : the "Indice Diatomique Pratique" (IDP), the "Indice Diatomique Générique" (IDG), the Sládecek Index (SLA) and the Trophic Diatom Index (TDI). These indices are different by the assigned indicative values and pollution sensitivity coefficients relative to every species and by the taxonomic list integrated in the calculation of every index. The spatio-temporal variation of these indices reflects clearly the deterioration of water quality downstream the wastewater input of Mediouna agglomeration (IDP=3,86 ± 2,30; IDG=6,05 ± 2,31; SLA=4,35 ± 2,62; IDT=5,80 ± 1,85) and its recovery after the swampy zone at the station HP (IDP=9,37 ± 2,35; IDG=11,83 ± 1,77 ; SLA=7,19 ± 3,05 ; IDT=6,76 ± 2,48). Among these indices, only the IDP presents a significant correlation (0,63 ; α<5%) with the IPO (reference index). While the IDG, the SLA and the TDI don't show a significant correlation with this index (0,38 ; 0,27 and -0,11 respectively). The IDT shows nearly the same water quality in the different stations and rather inform on the high level of eutrophication in these water courses.The physical and chemical analyses, the composition of diatom communities as well as the relative results of diatom indices, show that the oued Hassar stream is submitted to an important pollution, particularly downstream the wastewater input. Among the tested indices, the IDP appears more adapted to the assessment of water quality in oued Hassar. However, more work is required in order to finalize a new diatom index which is more adapted to characteristics of the Moroccan water courses

Composition en acides aminés libres et combinés et en vitamines de la microalgue Micractinium Pusillum Fres. issue d'un lagunage naturel

Dans ce travail est présentée la composition biochimique en acides aminés (AA) libres et combinés et en vitamines de Micractinium pusillum isolée à partir du lagunage naturel expérimental de Ouarzazate où cette microalgue prolifère pendant la période chaude. M. pusillum est produite en culture en vrac, sur milieu synthétique, dans des conditions de lumière et de température fixes. Cette étude révèle la richesse de M. pusillum en acides aminés combinés qui constituent environ 59% de sa matière sèche. Les acides aminés libres forment 3,4% de cette matière. Dix-sept acides aminés et quatre vitamines (D3, B2, B3, et B12) ont été déterminés chez cette microalgue.The biotechnological exploitation of microalgae requires more investigations in order to improve our knowledge of their biochemistry and to look for new potentially interesting species. Microalgae are used in various areas. Among them, wastewater treatment in wastewater stabilisation ponds and high-rate ponds is widely prevalent. Beside their purifying ability, their abundance in these ecosystems makes them interesting as a potential source of valuable products.Micractinium pusillum Fres, a green alga (Chlorophyceae) that grows in these ecosystems, was isolated from the experimental wastewater stabilisation pond of Ouarzazate city (south of Morocco), where it becomes important during the hot period. In the present work, we investigated the dissolved free and combined amino acids and the vitamins produced by this microalgal strain cultured on a mineral medium. The biomass production of M. pusillum was conducted in 2 l cotton-stoppered flasks under continuous light (60 µE m-2 s-1) provided by neon tubes and at a temperature of 24 ± 2°C. The culture medium was sterilised by autoclaving before inoculation. Free and combined amino acids were respectively analysed by HPLC separation of fluorescent o -phthaldialdehyde (OPA) derivatives. Prior to derivatization, the cells were broken and the cell content was digested with HCl. The analysis of vitamins was also realised by HPLC, with UV - visible detection methods, after extraction by appropriate solvents.The results reveal a high content of combined amino acids of approximately 59% (dry matter). Free amino acids constitute 3.4% (dry matter). Seventeen amino acids have been identified in this microalga (Table 1): aspartic acid, glutamic acid, arginine, methionine, phenylalanine, alanine and lysine were the principal components. The analysis of spectra indicated the presence of six categories of amino acids (AA) (Table 2): aliphatic AA, hydroxy AA, sulphur-containing AA, basic AA, aromatic AA and the diacid AA. Aliphatic AA (glycine, valine, leucine, and isoleucine) largely dominated the total AA pool, with more than 27% of total AA. Diacids AA (aspartic and glutamic acids), at approximately 25%, came in the second rank. Dibasics AA (15%) were relatively more abundant than aromatics AA (11%) and sulfur-containing AA (8%). It should be noted, however, that among the sulphur-containing AA, only methionine was detected by the method used in this work. Hydroxy AA are much less represented with only 4% of the total AA.Four vitamins were detected in M. pusillum (Table 3): vitamins D3, B2, B3, and B12. The content of vitamin D (6970 µg g-1) was highest, followed by vitamin B3 (2820 µg g-1) and vitamin B12 (1860 µg g-1). Vitamin B2 constituted 406 µg g-1. According to the reported values of vitamin contents in several other microalgal species, as well as some conventional foods (Table 5), it appears that M. pusillum species contains relatively important amounts

Ecological factors affecting the distribution of zooplankton community in the Massa Lagoon (Southern Morocco)

In this study, the zooplankton structure and the water quality of Massa Lagoon were investigated. Samples were collected biweekly at the three stations for 6 months from winter to summer 2008. Results show that the state of the lagoon is a hyper-eutrophic environment, characterized by high levels of chlorophyll-a and nitrogen. Pollution-tolerant zooplankton such as Brachionus was the dominant species in the lagoon. A total of 61 taxa were recorded, including 35 rotifers, 13 copepods, 5 ostracods, 6 protozoa and 6 cladocera. Salinity and nutrients in the water were the main environmental factors that affected the distribution of the zooplankton species.Key words: Massa Lagoon, zooplankton, environmental factors

Premier rapport sur la prolifération de marées jaunes ichthyotoxiques à Prymnesium parvum Carter (Haptophyceae) dans le lac hypereutrophe Oued Mellah (Maroc)

Les algues Prymnesiophyceae ou Haptophyceae (Chrysophyta) renferment des espèces capables de pullulations spectaculaires nommées " marées jaunes ". Parmi les Haptophycées, les plus communes sont : Prymnesium parvum, Prymnesium patelliferum et Chrysochromulina polylepis. Ces microalgues ont été souvent incriminées dans des cas de mortalité aiguë de poissons et d'invertébrés aquatiques. P. parvum est connue depuis cent ans comme responsable de blooms toxiques ayant entraîné des mortalités catastrophiques de poissons dans diverses régions du monde.Au Maroc, ces blooms à Prymnesiophyceae n'ont, jusqu'à présent, jamais été signalés. Nos recherches sur les successions phytoplanctoniques du lac hypereutrophe et saumâtre de Oued Mellah (33°30'N-07°20'W), ont mis en évidence la prolifération périodique en automne de l'Haptophycée P. parvum occasionnant des blooms spectaculaires. Les densités cellulaires de P. parvum, espèce dominante, atteignent des maxima de 148·106 cellules·L-1 en 1998 et 169·106 cellules·L-1 en 1999, représentant 34 à 80 % de la biomasse totale. Ces " marées jaunes " coïncident régulièrement avec des mortalités catastrophiques de poissons et d'invertébrés aquatiques dans le lac laissant présager une toxicité aiguë de cette souche de microalgue.Dans ce travail sont présentés les premiers résultats concernant la dynamique interannuelle des blooms à P. parvum et l'influence des conditions physicochimiques particulières des eaux du lac sur leur développement est discutée.The Prymnesiophyceae or Haptophyceae (Chrysophyta) contain species-forming spectacular blooms named yellow tides. Among Haptophyceae, Prymnesium parvum, Prymnesium patelliferum and Chrysochromulina polylepis are the most common. These microalgae were often involved in acute fish and aquatic invertebrates mortality cases. P. parvum, known since hundred years as being responsible for toxic blooms, has induced catastrophic fish mortality in various areas throughout the world.In Morocco, blooms of Prymnesiophyceae have never been reported up till now. Studies on phytoplankton successions in the hypertrophic brackish Oued Mellah lake (33°30'N-07°20'W) show a periodic autumnal proliferation of P. parvum. This species, which cellular densities reach a maxima of 148·106 cells·L-1 in 1998 and 169·106 cells·L-1 in 1999, dominates the other phytoplanctonic species with 34 to 80% of the total biomass. The yellow tides coincide regularly with dramatic fish and aquatic invertebrates mortality in the lake leading to the prediction of an acute toxicity due to this microalgae.The principal aim of this study was to present the first results concerning the interannual dynamics of P. parvum blooms and to discuss the influence of the particular physical and chemical water characteristics on their development

Seasonal characterization of the nutrients state in Oualidia Lagoon (Moroccan Atlantic coast)

The nutrient cycle in Oualidia lagoon, on the Atlantic Moroccan coast, was studied at both spatial and temporal scales, covering spring and summer conditions. Water samples were collected bimonthly at high tide from March to August during years 2011 and 2012 at six stations distributed throughout the lagoon. The physico- chemistry (temperature, salinity, dissolved O2) and nutrient enrichment of the lagoon surface water were monitored. The average nutrient concentration of surface water were 14.4 μmol.l-1 and 28.1 μmol.l-1 for NH4+, 20.4 μmol.l-1 and 19.9 μmol.l-1 for PO43- and 3.7 μmol.l-1 and 7.6 μmol.l-1 for NO2- in 2011 and 2012, respectively. Strong seasonal differences of nutrient distribution at the different stations were noticed. Temperature, salinity and dissolved O2 were correlated with nutrient concentrations, all parameters showing low spatial (inter-station) variability. Hydrological conditions exert a major control on the nutrient cycling in the lagoon. Results of this study are important to increase the richness on the scientific knowledge of nutrient dynamics along the Moroccan Atlantic coast, particularly in the semi-enclosed lagoons that are important transitional systems.Peer reviewe