Population dynamics of Pseudo-nitzschia species (bacillariophyceae) in the near shore waters of Dar es Salaam, Tanzania

The genus Pseudo-nitzschia is a chain-forming diatom comprising about 30 species some of which are known to produce domoic acid (DA) that causes amnesic shellfish poisoning (ASP). The current study aimed at assessing the population dynamics of Pseudo-nitzschia in the near shore waters of Dar es Salaam. Samples were collected between August 2008 and July 2009 from two stations. The first station was located in the open waters off Mbudya Island and the second was located at a point in-between Kunduchi and Mbudya Island. Three Pseudo-nitzschia species, i.e., Pseudo-nitzschia pungens, Pseudo-nitzschia seriata and Pseudo-nitzschia cuspidata wereencountered with Pseudo-nitzschia pungens being the most abundant. The concentration of Pseudo-nitzschia species ranged from none in various samples to a highest value of 16 cells/L recorded in September 2008. There was no significant difference in the abundance of Pseudonitzschiaspp. between site 1 and 2 and between the northeast (NE) and southeast (SE) monsoon periods. The abundance of Pseudo-nitzschia spp. was below concentrations reported elsewhere to cause problems to shellfish  consumers implying that shellfish collected near Dar es Salaam may be ASP free. However, further studies are required to ascertain DA production in coastal waters of Tanzania.Key words: Pseudo-nitzschia dynamics, amnesic shellfish poisoning, Tanzania

Recent trends in accumulation rate, elemental and isotopic composition of organic matter in the Magu bay, Lake Victoria

Stable isotope composition of organic carbon (OC), 14C data, OC and nitrogen content of recently deposited sediments in Magu Bay of Speke Gulf, Lake Victoria are used to document accumulation rates, sources and distribution of organic matter in the bay. The stable isotope values of both organic carbon and nitrogen decrease towards offshore, and this trend is associated with increase in the contents of organic carbon and nitrogen. The isotope results show that the organic material deposited in the bay are generally derived from C4 type of plants and are not transported far from the river mouth. Also the results show that preservation of organic matter is high in open water probably due to high primary productivity owing to high concentration of nutrients and low in turbidity. Low isotope values in offshore sites indicate that the available stock of nutrients far exceeds the demand. Sedimentation rates in the bay are not high and range from 5 to 54 cm/ka. This could be attributed to trapping efficiency by shoreline aquatic macrophyte. Furthermore, the mean accumulation rates of organic carbon and nitrogen for the bay, range from 6.92 to 57.25 gC/m2/yr and 0.51 to 4.37 gN/m2/yr, respectively, and show that Magu Bay is currently experiencing eutrophication. Tanzania Journal of Science Vol. 31 (1) 2005: pp. 23-3

Diurnal expression of hetR and diazocyte development in the filamentous non-heterocystous cyanobacterium Trichodesmium erythraeum

The marine non-heterocystous cyanobacterium Trichodesmium fixes atmospheric N2 aerobically in light. In situ immunolocalization/light microscopy of NifH revealed that lighter, non-granulated cell regions observed correspond to the nitrogenase-containing diazocyte clusters in Trichodesmium IMS101. The number of diazocyte clusters per trichome varied from 0 to 4 depending on trichome length. The constant percentage of diazocytes (approx. 15 %) in cultured strains and five natural populations suggests a developmentally regulated differentiation process. Real-time RT-PCR showed that ntcA, encoding the global nitrogen regulator in cyanobacteria, and hetR, the key regulatory gene in heterocyst differentiation, are both constitutively expressed during a 12 h/12 h light/dark cycle. hetR in addition showed a distinct peak in the dark (close to midnight) while nifH expression commenced 6–8 h later. The expression of all three genes was negatively affected by addition of ammonia. Some early heterocyst differentiation genes were also identified in the genome of Trichodesmium. The data suggest that hetR and ntcA may be required for development and function of diazocytes in Trichodesmium

Effect of nutrient enrichment on seagrass associated meiofauna in Tanzania

Abundance, diversity and community structure of meiofauna, with special emphasis on epiphytic harpacticoid copepods, occurring in Tanzanian seagrass beds under various nutrient inputs was determined. All measured parameters for epiphytic meiofauna and diatoms (fucoxanthin) were negatively affected by nutrient input and this was detected even at the higher taxonomic levels of meiofauna, supporting the validity of higher taxon surrogacy in environmental impact studies. However, benthic meiofauna and other biofilm characteristics (chlorophyll a) did not show any difference between sites suggesting that nutrient enrichment had less impact on these variables. This indicates a differential impact of pollution on epiphytic vs. benthic communities. Consequently, different trophic levels will be impacted in various ways and hence the effects of pollution on the overall ecosystem functioning of seagrass beds are complex and not straightforward. Although the seagrass plants themselves don't show any major changes under different nutrient input, associated organisms that guarantee energy flow at basal levels of the food web in this ecosystem can be largely impacted

Spatial and temporal variations in the abundance and diversity of phytoplankton in Lake Manyara, Tanzania

This study evaluated the temporal dynamics of phytoplankton species diversity and abundance in relation to some physico-chemical parameters in Lake Manyara for a period of fourteen consecutive months (between July 2007 and August 2008). The aim was to relate the temporal variability in the physico-chemical parameters of the lake to the abundance and diversity of phytoplankton. Three sampling sites were established in the lake, and data were collected once every month. Electrical conductivity, salinity, water temperature, dissolved oxygen; turbidity, transparency and pH were measured in-situ using a water quality checker Water samples for nutrients and phytoplankton abundance and species composition were analysed at the University of Dar es Salaam. In the laboratory, the concentration for inorganic nutrients were determined using a Shimadzu UV-spectrophotometer. Salinity and pH values in the lake ranged from 0.1 ‰ to 40 ‰ and from 6.23 to 10.67 respectively. However, there were shift in phytoplankton community dominance between Anabaena sp to Arthrospira sp likely due to differences in salinity and pH thresholds requirements. Nitrate, phosphate and ammonium concentrations ranged from 0.5 to 3.2 μg/l, 0.5 to 570 μg/l and 0.5 to 10.5 μg/l respectively while conductivity varied between 8.7 to 84.5 mS/cm. Other cyanobacterial genera, Phormidium, Oscillatoria, Spirulina, Aphanocapsa and Synechoccocus were also common. The results indicated that phytoplankton assemblage was positively correlated with ammonium, phosphate, dissolved oxygen, conductivity and nitrateTanzania National Park and ACM-UDS

Spatial and temporal variations in the abundance and diversity of phytoplankton in Lake Manyara, Tanzania

This study evaluated the temporal dynamics of phytoplankton species diversity and abundance in relation to some physico-chemical parameters in Lake Manyara for a period of fourteen consecutive months (between July 2007 and August 2008). The aim was to relate the temporal variability in the physico-chemical parameters of the lake to the abundance and diversity of phytoplankton. Three sampling sites were established in the lake, and data were collected once every month. Electrical conductivity, salinity, water temperature, dissolved oxygen; turbidity, transparency and pH were measured in-situ using a water quality checker Water samples for nutrients and phytoplankton abundance and species composition were analysed at the University of Dar es Salaam. In the laboratory, the concentration for inorganic nutrients were determined using a Shimadzu UV-spectrophotometer. Salinity and pH values in the lake ranged from 0.1 ‰ to 40 ‰ and from 6.23 to 10.67 respectively. However, there were shift in phytoplankton community dominance between Anabaena sp to Arthrospira sp likely due to differences in salinity and pH thresholds requirements. Nitrate, phosphate and ammonium concentrations ranged from 0.5 to 3.2 μg/l, 0.5 to 570 μg/l and 0.5 to 10.5 μg/l respectively while conductivity varied between 8.7 to 84.5 mS/cm. Other cyanobacterial genera, Phormidium, Oscillatoria, Spirulina, Aphanocapsa and Synechoccocus were also common. The results indicated that phytoplankton assemblage was positively correlated with ammonium, phosphate, dissolved oxygen, conductivity and nitrateTanzania National Park and ACM-UDS