Taxonomic studies of gracilarioid algae (Gracilariales, Rhodophyta) in Tanzania and their potential for utilization

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University of Dar es Salaam
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.
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark ( THS EAF QK569.G8B87)
Gracilaria, Red algae, Algae, Tanzania
Buriyo, A S (2006), Taxonomic studies of gracilarioid algae (Gracilariales, Rhodophyta) in Tanzania and their potential for utilization, Master dissertation, University of Dar es Salaam.