I. A. Kobbia

Effect of pH on growth and biochemical responses of Dunaliella bardawil and Chlorella ellipsoidea

The goal of the present investigation was to study the effect of pH on growth and biochemical responses of Dunaliella bardawil and Chlorella ellipsoidea when exposed to different pH values. The two tested microalgae could grow in a wide range of pH (4–9 for D. bardawil and 4–10 for C. ellipsoidea). The dry weight gain and the biochemical components of D. bardawil were greatly enhanced at pH 7.5. In contrast, dry weight and carbohydrate content of C. ellipsoidea attained their maximum values at the alkaline pH. On the other hand, the protein content of C. ellipsoidea recorded its highest value at pH 4, while the pigment content of the same alga was highest at pH 4, 6, and 7.5 and decreased at alkaline pH. Both pH 6 and pH 9 stimulated the accumulation of β-carotene, vitamin E and vitamin C in D. bardawil, with the highest values of the three compounds recorded at pH 9. In the case of C. ellipsoidea, β-carotene content increased at pH 6 and pH 10 as compared with the control, but the amount of β-carotene was much higher at pH 6 than at pH 10. Vitamin E content was higher in C. ellipsoidea cells at pH 10 than at pH 6. Both pH 6 and pH 10 caused a significant decline in vitamin C content of C. ellipsoidea.

Toxic Effect of Certain Metals Mixture on Some Physiological and Morphological Characteristics of Freshwater Algae

The toxic effect of multi metals mixture which exist simultaneously in aquatic ecosystem on natural phytoplankton assemblages (green algae, blue-green algae and diatoms) was studied. For this purpose a laboratory scale unit was designed to evaluate the effect of continuous flow metals mixture in forms if triple and penta metals in Nile water algae. Clear changes in algal biomass in terms of chlorophyll a (chl a) took place when subjected to metals combination. The rise or decline in chl a was in relation with other algal pigments (chl b, chl c, carotenoides and phenophytin), protein and carbohydrate content of algal cells. Substantial changes in phytoplankton community structure was detected and the most tolerant group was blue-green algae followed by green algae while diatoms was the most sensitive group. The most dominant species in all cases were blue-green alga Oscillatoria mougeotii and green alga Scenedesmus quadricauda. In addition clear changes in morphological shape was observed for tolerant species belonging to the three algal groups. Nile water algae has ability to remove and accumulate metals in the following order therefore Zn > Cd > Ni > Cu > Cr. In addition, phytoplankton has ability to recovered from the stress of metals when eliminated from the media and the recovered biomass was nearly equivalent to that before exposing to metals stress. The overall effect of metals mixture depending on the type and number of metals, the algal community structure and ratio between different morphological forms of algae (unicellular, colonial and filamentous).

Effect of thiobencarb on growth and photosynthesis of the soil alga Protosiphon botryoides (Chlorophyta)

The effects of the herbicide thiobencarb (Saturn) were tested on the growth and physiology of the chlorophyte Protosiphon botryoides isolated from an Egyptian paddy. Assays were conducted using 16-day batch cultures. Chlorophyll and dry weight biomass yields were significantly reduced at 2–3 mg L-1 thiobencarb, and dark respiration increased and protein decreased significantly at 3 mg L-1. Reductions in exponential specific growth rate (μ) were generally small, but in some cases significant. Thiobencarb also slightly, but significantly, reduced the 77 K fluorescence parameter Fv/Fm, an indicator of maximum photosynthetic efficiency. No consistent dose-dependent changes occurred in chlorophyll per unit dry weight, total carbohydrate or gross photosynthetic capacity. Whereas half of the added thiobencarb was recovered from control (uninoculated) medium, it was largely absent from cells and culture medium after sixteen days, indicating biodegradation by the alga or associated bacteria. P. botryoides recovered fully within sixteen days following subculture in thiobencarb-free medium. Independently varying phosphate and nitrate nine-fold had no clear effect on the sensitivity of P. botryoides to thiobencarb.

Impact of phosphorus loadings on macro-algal communities in the Red Sea coast of Egypt

This study was undertaken to investigate the impact of phosphorus loadings on the seasonal abundance and diversity of macro-algal communities at three sites of the Egyptian coastal region of the Red Sea. Sea-water analysis revealed no significant variations in the levels of dissolved inorganic carbon at these sites. Nitrate content was highest during the winter season especially at Ghardaqa. The localized phosphate pollution at the two other sites significantly increased the phosphate level in water which led to significant decreases in biomass of the macroalgae as compared to Ghardaqa. The intertidal zone at one of the impacted sites supported very poor algal vegetation, dominated by Phaeophyta in winter and spring and Rhodophyta in summer and autumn; at Quseir it was dominated by microfilamentous Rhodophya. At Ghardaqa, the intertidal macro-algal community was dominated by Phaeophyta. The results also showed that the abundance of marcroalgae reached its maximum in August at all the study sites, and that species diversity was significantly higher at Quseir than at the other two sites.

Growth criteria of two common cyanobacteria isolated from Egyptian flooded soil, as influenced by some pesticides

Higher rates of the two organophosphorus Insecticides (dimethoate and dursban) induced severe drop in the dry weight gain of Nostoc muscorum and Anabaena oryzae. The fungicide karathane seemed to be inhibitory to the growth of Anabaena whereas all levels of the fungicide, except the two higher stimulated the growth of Nostoc. Trifluralin at all levels inhibited the growth of both organisms. However the magnitude of inhibition was always more pronounced in Anabaena. The lowest concentrations of dursban and dimethoate favored chlorophyll a synthesis in the cells of both cyanobacteria. Contrary to chlorophyll, total carotenoid accumulation was significantly suppressed. Moderate and higher doses of karathane and trifluralin increased chlorophyll a biosynthesis in Nostoc and to lesser extent in Anabaena, a phenomenon that was accompanied by significant increase in total carotenoid content. Glucose uptake by both organisms from media was accelerated following adminestration of all pesticides, an effect that was intensified with further increase in concentrations. Dimethoate and dursban favored the total carbohydrate accumulation in the cells of both organisms, whereas karathane and trifluralin accentuated the process, more prominently in Nostoc.

Seasonal Changes in Cystoseira Myrica and Phosphorus Input at Two Sites of the Red Sea Egyptian Coast

Elevated phosphate concentrations at Safaga and Quseir, Red Sea, Egyptian coast, were related to some ecological and nutritional aspects of the macro-algaCystoseira myrica during 1985. The results obtained were compared with those recorded for a non-polluted control site at Ghardaqa.Chemical analysis of surface seawater samples revealed that the concentrations of dissolved phosphate at Safaga and Quseir were 3 and 20 times as much as that at Ghardaqa, respectively. The standing crop ofC. myrica showed two peaks in spring and autumn. Maximum biomass yield (491 g m−2) and number of individuals (127 m−2) ofC. myrica were recorded in the spring at the Ghardaqa site. QuseirC. myrica samples contained significantly higher protein-N, total-N and total-P values but lower carbohydrate values than the Safaga and Ghardaqa samples (LSD at 1% level). Tissue N:P molar ratios forC. myrica, Laurencia papillosa andUlva lactuca collected from Ghardaqa ranged from 68–98, compared to 30–59 for the same species collected at the phosphorus polluted sites at Safaga and Quseir. The carbon levels and the C:N ratios ofC. myrica exhibited no significant variations in the three studied sites. However, the C:P ratios of Ghardaqa plants were significantly higher than those of Safaga and Quseir.