Browsing by Author "Buriyo, Amelia Sylvery"

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    The effect of seasons on yield and quality of agar and carrageen from selected Tanzanian red algal species.
    (University of Dar es Salaam, 1999) Buriyo, Amelia Sylvery
    The effect of seasons on yield and quality of agar and carrageenan from four Tanzanian red algal species, namely Gracilaria crassa, Eucheuma den ticulatum, Sarconema filiforme and Hypnea musciformis was studied. Samples were collected from Oyster bay rocky shore, Dar es salaam. The study was carried out between June 1996 and May 1997. Seaweed samples were collected, once a month during spring low tide. Thereafter samples were dried, extracted and the resultant phycocolloid was used to determine yield and quality. Biomass and thallus nitrogen and phosphorus content were determined seasonally in four months during wet and dry Southeast monsoon (SE) and Northeast monsoon (NE) periods. Percentage ash content was determined monthly. During each sampling visit, light, temperature, salinity and pH were recorded. Meteorological data were obtained from the Directorate of Meteorology, Dar es Salaam Tanzania. Trial cultivation of Sarconema filiforme under varying light intensity and nutrient levels was carried out in the laboratory for a period of a month for every experiment. Results indicate that red algal species were most dominant in terms of species number and biomass during November to January. This may be attributed to nutrient availability (particularly N) and calmer conditions prevailing in the sea. Another algal abundance peak was observed during May to July when total nitrogen concentration in the seawater was also high, light and temperature were low. Reduced temperature and insolation serves intertidal plants from stresses induced by photoinhibition and desiccation. The mean phycocolloid yield and quality were noted to vary with seasons within the species and between species. The agar yield from G. crassa was significantly higher during the NE monsoon period (t = 3.16, P<0.05). E. den ticulatum and S. filiforme had a significantly higher mean carrageenan yield during the SE monsoon period while carrageenan yield of H. musciformis was not significantly different between the monsoons (t = 6.15, P<0.05; t = 6.54, P<0.05 and t = 0.55, P>0.05, respectively). Generally, the presence of higher carrageenan yield during the SE monsoon period could be attributed to favourable physical and nutritional conditions. Also high turbulence during this season might have signalled algae to synthesize more supporting cell wall material. The mean phycocolloid quality (gel strength) of G. crassa, S. filiforme and H. musciformis was relatively higher during the SE monsoon period though the difference between seasons was significant only in the carrageenan quallity of S. filiforme (t = 0.86, p<0.05 and t = 1.91, p>0.05, respectively). Carrageenan from E. denticulatum had significantly higher gel strength during NE monsoon period (t = 2.61, p<0.05). There was a generalized low gel strength during the rainy periods. This was due to low salinity and possibly inadequacy of essential cations for phycocolloid gelation. For S. filiforme grown in the laboratory, growth rates and carrageenan yield were significantly higher in plants grown at higher light intensity (F= 1550.73, P<0.05 and F=2047.46, P<<0.05) respectively and nitrogen-enriched growth medium (F= 458.99, P<0.05 and F= 908.95, p<<0.05) respectively.
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    Taxonomic studies of gracilarioid algae (Gracilariales, Rhodophyta) in Tanzania and their potential for utilization
    (University of Dar es Salaam, 2006) Buriyo, Amelia Sylvery
    Gracilarioid algae were surveyed from 44 locations, in various habitats of the intertidal and upper subtidal zones along the coastal regions of Tanzania between January 2002 and July 2003 with the view to (i) establish their phylogenetic relationships (ii) map their distribution and (iii) assess their seasonal variation in cover, agar yield and its quality. Based on the nucleotide sequences comparison of the nuclear-encoded small subunit (18S) rDNA of II Tanzanian gracilarioid populations and other 32 taxa of Gracilariaccac from the GenBank by maximum likelihood (ML), maximum parsimony (MP) and neighbor-joining (NJ) (i) three distinct lineages named CurdiealMelanthalia, Gracilariopsis and Gracilaria were retrieved and (ii) eight Gracilaria and one Gracilariopsis distinct taxa were obtained from Tanzanian populations. Of the nine taxa obtained, one Gracilaria and one Gracilariopsis species are described for the first time in Tanzania. Gracilaria canaliculala, G. debilis and G. salicornia showed to be taxonomically distinct taxa. These results were further supported by the anatomy of reproductive structures. G. crassa was reduced to a synonym of G. canaliculala, G. fergusonii to G. debilis and G. verrucosa to Gracilariopsis sp. It is therefore, concluded that G. verrucosa does not occur in Tanzania; morphologically related taxa are not necessarily phylogenetically related and a combination of morphological and molecular techniques is a useful tool for resolving the existing taxonomic problem in gracilarioid algae in Tanzania. With regard to distribution patterns, seasonality on standing stock, agar yield and properties, it was found that G. corlicata, G. debilis and G. salicornia were the most common species and G. arcuata, G. canaliculata, G. foliifera, Gracilaria sp and Gracilariopsis sp had restricted distribution. Percentage canopy cover was generally higher during SE monsoon period and G. salicornia ranked higher. G. debilis and G. salicornia with mean agar yield (in percentage dry weight) of around 33.8 ± 5.1 and 22.7 ± 6.6 and gel strength (in g cm'2) of about 186.5 ± 50.8 and 194.4 ± 36.7, respectively, are the potential candidates for agarophytes mariculture in Tanzania. Commercial agar prepared in the same way had gel strength of about 470 g cm . The best period for their harvesting from wild populations is during the dry NE monsoon period.