Browsing by Author "Kyewalyanga, Margareth"

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The decline in phytoplankton biomass and prawn catches in the Rufiji-Mafia Channel, Tanzania
(African Journals Online, 2016-11-27) Semba, Masumbuko; Kimirei, Ismael; Kyewalyanga, Margareth; Peter, Nyamisi; Brendonck, Luc; Somers, Ben
The world’s oceans have seen significant declines in phytoplankton-the primary food source in the marine environment. This decline in primary producers is likely to impact the food chain and functions of most coastal and marine ecosystems. Despite being one of the most productive marine fishing grounds in the Western Indian Ocean (WIO) region, the information about phytoplankton biomass in the Rufiji-Mafia Channel is poor. This study aimed to narrow this information gap by assessing phytoplankton biomass in the Channel and its association with the decline of the prawn fishery. We combined in-situ measurement and ocean colour satellite data to determine and assess trends in phytoplankton biomass and sea surface temperature between 2002 and 2014. These trends were related to a declining prawn fishery in the Channel. While phytoplankton displayed a significant declining trend during the southwest monsoon, sea surface temperature showed an insignificant increasing trend. Phytoplankton declined at the rate of 1.2 percent per year (tau = 1.2, z = 3.52, p = 0.004) between 2002 and 2014. This declining trend in Chl-a matches well with the decreasing trend in the prawn fishery (tau = 0.57, z = 3.39, p = 0.0006) and the insignificant increasing trend in sea surface temperature (tau = 0.02, z = 0.43, p = 0.66). This study provides quantitative evidence of trends in chlorophyll and SST and the link with trends in the prawn fishery, which increases our understanding of the changes in marine primary productivity in the coastal waters of Tanzania.
Seasonal variability of vertical patterns in chlorophyll-a fluorescence in the coastal waters off Kimbiji, Tanzania
(Western Indian Ocean Journal of Marine Science, 2021-09-24) Peter, Nyamisi; Semba, Masumbuko; Lugomela, Charles; Kyewalyanga, Margareth
A study on the vertical pattern of chlorophyll-a (Chl-a) fluorescence was undertaken in the Mafia Channel off Kimbiji, Tanzania. Data was collected during the Southeast Monsoon (SEM) and Northeast Monsoon (NEM) seasons. There was higher Chl-a concentration of 0.1 to 1.1 mgm-3 in the surface layer off Kimbiji to about 50 m depth due to the presence of mixed layer depth (MLD) which allowed water mixing in the layer. A deep Chl-a maximum was recorded at around 40 m depth during the NEM and between 40 and 70 m in the SEM. Surface water between lon gitude 39.9°E and 40.2°E had low Chl-a from the surface to about 50 m depth due to poor nutrient input. The NEM had an insignificantly higher Chl-a value than the SEM (p > 0.05) which differed from other studies in which Chl-a was higher during the SEM than the NEM, than, the Chl-a concentration was higher at the surface during the SEM than during the NEM. Satellite data showed higher Chl-a in the SEM than NEM, localized along the Mafia Channel. During the SEM season the wind pushes higher Chl-a water from the Mafia Channel towards the north and leads to a higher concentration at Kimbiji
Spirulina (Arthrospira fusiformis, Gomont 1892) as a High-Quality Feed Ingredient for Nile Tilapia Fingerlings
(Tanzania Journal of science, 2023-08-23) Michael, Angelina; Kyewalyanga, Margareth; Lugomela, Charles
A partially randomized experimental design was conducted to evaluate the effect and potential of spirulina species (Arthrospira fusiformis) isolated from Momela Lakes, Tanzania, on the growth, antioxidant capacity, feed utilization, and body composition of Nile tilapia fingerlings. Five dietary treatments were formulated, including spirulina meal at 5%, 10%, and 15% of the total diets, as well as control diets with freshwater shrimp or Lake Victoria sardine. The protein content of the experimental diets was 25, 28, and 35% for a treatment containing spirulina at 5, 10, and 15% inclusion, respectively, while the control diets had 35% crude protein each. After eight weeks of feeding, fish fed with a lower inclusion level of spirulina showed the best growth performance and feed utilization efficiency, similar to the fish fed with control diets. The group fed with 5% spirulina exhibited excellent protein efficiency ratio compared to all other fish groups. All spirulina-fed fish groups demonstrated higher protein deposition and strong antioxidant activity against free radicals compared to those fed with control diets. In conclusion, spirulina proves to be a superior feed ingredient for high-quality Nile tilapia farming, providing comparable results to control feeds