Browsing by Author "Mahongo, S.B."

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    Coastal upwelling and seasonal variation in phytoplankton biomass in the Pemba Channel
    (WIOMSA, 2020) Kyewalyanga, Margareth S.; Peter, Nyamisi; Semba, M.; Mahongo, S.B.
    This study was conducted in the Pemba Channel off Tanga Region in northern Tanzania to investigate physical and chemical factors that drive changes in phytoplankton biomass. Three transects off Mwaboza, Vyeru and Sahare were selected. For each transect, ten stations were sampled. Phytoplankton biomass was determined as chlorophyll-a (Chl-a) concentration. Similarly, physico-chemical variables (temperature, salinity, dissolved oxygen, pH and nutri ents) were determined. It was observed that the Chl-a concentration was significantly higher during the northeast monsoon (median 1.44 mg m-3) as compared to the southeast monsoon (median 1.19 mg m-3; W = 2216, p = 0.029). The higher productivity during the northeast monsoon is attributed to the presence of high-nutrient water caused by coastal upwelling. It is concluded that indication of upwelling, observed through relatively low temperatures during the northeast monsoon season, could be responsible for bringing nutrient-rich waters to the surface, which in turn stimulated the increase in Chl-a concentration.
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    Employing multivariate analysis to determine the drivers of productivity on the North Kenya Bank and in Kenyan territorial waters
    (WIOMSA, 2020) Kamau, J.; Ochala, O.; Ohowa, B.; Mitto, C.; Magori, C.; Osore, M.; Mahongo, S.B.; Kyewalyanga, M.S.
    A complex mix of natural processes exist in nearshore and offshore waters which influence coastal and marine ecosystem productivity. An understanding of the biogeochemical processes involved is a key element in interdis ciplinary studies of primary production, oceanic flux and storage of carbon dioxide. Water circulation in the East African region is influenced by coastal currents driven by monsoon winds. There are four oceanic currents influenc ing Kenya’s coastal waters; namely the East African Coastal Current, the Somali Current, the Southern Equatorial Current and the Equatorial Counter Current. The Kenyan fishing industry is slowly embracing offshore fishing grounds, and the North Kenya Bank is emerging as the next fishery frontier. This study aims to provide insight on the processes driving the productivity of Kenya’s territorial waters. The variable Si* (the difference between available silicate [Si(OH)4] and nitrate [NO3- ]) was employed as a proxy of upwelling. It was highly positively correlated to chlorophyll-a, indicating that upwelling is a major phenomenon driving productivity in Kenyan territorial waters. Particulate Organic Carbon (POC) and Dissolved Oxygen (DO) exhibited a lesser positive correlation with chloro phyll-a, implying that remineralization also has some influence in the productivity of the area.