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University of Namibia (2015)

A taxonomic, ecological and nutritional study of Porphyra Capensis Kutzing population from the Namibian coast

Kavishe, D

Titre : A taxonomic, ecological and nutritional study of Porphyra Capensis Kutzing population from the Namibian coast

Auteur : Kavishe, D

Université de soutenance : University of Namibia

Grade : Doctor of Philosophy in Science (Biology) 2015

Résumé
The Namibian Porphyra capensis Kützing was studied as very little was known of its taxonomy, ecology, phylogeny or nutritional status. It was hypothesized that it was phlogenetically related to the South African P. capensis as they share common ancestry. DNA was extracted from thalli and partial sequences obtained from their 18SrDNA and ITS regions. GenBank sequences of interest were incorporated, alignments made and phylogenetic trees were generated using MEGA 5.1. The results showed the existence of a Namibian P. capensis clade, implying preliminarily that it is a subspecies. It was also hypothesized that the abundance (standing crop biomass and cover) of P.capensis along Lüderitz and Swakopmund shores would be similar because of similar environmental conditions created by the cold Benguela Current System. This was tested in tandem with another hypothesis that the frequeny of harvesting thalli from the field would not significantly affect annual yield as nutrients and propagules would constantly be replenished from the system. A best fit model describing the relationship between standing crop and percentage foliar cover of Namibian Porphyra was developed. Cover and standing crop biomass were not significantly different between Lüderitz and Swakopmund but standing crop biomass varied significantly with seasons (p=0.001). Harvesting frequency increased the mean annual yield (p=0.008). The regression power equation Y = with R2 = 0.649 was proposed as the best model for estimating biomass (Y, g) from cover (X, %) in the field while being cognizant of the relatively low coefficient of determination which resulted from its patchy distribution and multilayering of thalli. The hypothesis that the nutritional content of P. capensis was comparable to that of lettuce was tested and laboratory cultures on the Namibian P. capensis life cycle were also initiated. Nutritional analyses were carried out according to standard procedures and it was established that fibre and calcium were significantly higher in P. capensis (p=0.016 and p=0. 036 respectively) while fat was significantly higher in lettuce (p=0. 0026). Magnesium, phosphorus, crude protein, iron, carbon and β–carotene were not significantly different. The life cycle of P. capensis in laboratory cultures was completed. The study proposed a subspecies status to the Namibian P. capensis ; assessed its nutritional content while opening up possibilities for its mariculture to conserve wild populations. The study contributes to the promotion of P. capensis as a ‘health food’. Further taxonomic exploration of local Porphyra populations was recommended and a prudent use of the abundance model encouraged.

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Page publiée le 24 décembre 2015, mise à jour le 5 août 2017