Institute of Marine Sciences


Recent Submissions

Now showing 1 - 20 of 182
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    Intergrated Seismic Stratigraphic and Structural Analysis of the Songo Songo Gas-Field, Shallow Offshore Tanzania, Using Seismic and Well Data
    (Journal of Geology & Geophysics, 2019-03-16) Sabuni, Rachel
    Seismic stratigraphy and structural analysis of seismic data, when combined with wireline data, provides vital information for hydrocarbon exploration in a prospective basin. These techniques were employed in the Songo Songo shallow coastal basin, southern Tanzania to determine stratigraphic setting, trapping mechanism, reservoirs zones. Suites of well logs from two wells (AA-1 and BB-5) and 2-D seismic data was obtained from TPDC in the study area. Lithologic interpretation and well correlation were carried out using the well log suites. Stratigraphic analysis was carried out with the well logs and 2D seismic data by using principles of sequence stratigraphy while structural interpretation was done with aid of the seismic data to produce polar plots for the different structural trends. The lithology was dominated by sand, shale, and limestone. Five sequence boundaries (SB); SB1 (Albian), SB2 (base of Coniacian-Early Campanian), SB3, (Middle Eocene), SB4 (Late Miocene) and SB5 (Quaternary)) and three maximum flooding surfaces (MFS); MFS1-(Early Cretaceous), MFS2, (Late Cretaceous), MFS3-(Early Eocene) were identified. Three main normal faulting systems (Jurassic faults, active during the Jurassic rifting phase of Madagascar, Neogene faults that occurred during Neogene east African rifting and reactivated faults which mostly were Jurassic fault reactivated by east African rifting) of NNW-SSE were recognized in the study area. The structural interpretation reveal that the gas field is dominated by normal faults that occur in the upper and lower part of Songo Songo suggesting two phases of deformation prior to development of the field. The main reservoir is developed in the Neocomian and Albian sandstones, and capped by Jurassic faults and Wami (Formation) overlying rocks. The gas is sourced from Jurassic shale known as Mtumbei Formation and stored at the main reservoir developed in the Lower Cretaceous aged Neocomian sandstone known as Kipatimu Formation, sealed by high pressured shale of upper Cretaceous known as Wami Formation. This study shows that deposition of sediment occurs in the NW – SE direction, with the thinning of sediments thickness towards well BB-5 while the stratigraphic sections show that the horizons are laterally continuous and are being strongly affected by tectonic events.
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    Petroleum systems and hydrocarbon potential of the Ruvuma Basin, Tanzania
    (ELSEVIER, 2023-02-18) Sabuni, Rachel
    Ruvuma Basin is widely recognized across the world for large gas field discoveries, which indicate the presenceof gas-prone sources. However, little is known about the basin’s source rock’s hydrocarbon generation potential, including the distribution of significant petroleum systems. Inferences are often drawn from Permo-Triassic and Jurassic source rocks in Mandawa Basin, Tanzania and Morondava Basin, Madagascar. As a result, knowledge ofthe basin’s potential source rocks is not known. To constrain possible source beds including petroleum systems, this study thoroughly reviewed previous literature coupled with rock eval pyrolysis and vitrinite reflectance analysis on rock cuttings (n = 19) from the Ruvuma Basin’s Permo-Triassic, Jurassic, and Cretaceous shales of Lukuledi-1 well. The findings indicate variable petroleum systems with different generation potentialities in the Permo-Triassic, Jurassic, Cretaceous, and Cenozoic intervals. The Permo-Triassic plays sourced hydrocarbons from the matured Permo-Triassic shales of kerogen type II and I, with Total Organic Carbon (TOC) average of 40 %wt, Hydrogen index (HI) average of 286.5 mg HC/g TOC, vitrinite reflectance (Ro%) average of 0.81 with Tmax average of 436 ◦C capable of oil generation. The Jurassic play systems are charged from matured Jurassic kerogen type III and mixed type II/III shales with TOC~ 4 %wt, HI~54.25 mg HC/g TOC, Ro% ~0.6 and Tmax ~444 ◦C capable of gas generation. Cretaceous and the Cenozoic play systems, sourced hydrocarbon from deeper sources because their source rocks are thermally immature with kerogen type III, having TOC ~0.6 %wt, HI ~53.6 mg HC/g TOC, Ro% ~0.3 and Tmax <420 ◦C capable of gas generation. These results indicate that the Cenozoic play system incorporates hydrocarbons from diverse sources/reservoirs, making it a potential exploration target for future discoveries. These findings necessitate more research to determine migratory patterns, which will result in new ground-breaking discoveries in the basin.
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    Geologic review of hydrocarbons potential of the Rufiji Basin, Tanzania
    (Springer, 2022-04-15) Sabuni, Rachel; Mtelela, Cassy; Kagya, Meshack
    The Rufiji Basin is one of the underexplored and least studied basins in the coastal Tanzania, despite the occurrences of oil and gas seeps that indicate the presence of a working petroleum system(s). Consequently, geology and distribution of key petroleum elements and hydrocarbon potentiality of the basin remains poorly understood. This study presents a geological review of the hydrocarbon potential of the Rufiji Basin based on a synthesis of published and unpublished reports of multifaceted studies in the basin, coupled with very limited additional data collected in the course of this study. This review identifies three petroleum plays (play I, play II, and play III) along with associated components, and includes: hydrocarbons play I, which constitutes a Permian–Triassic source rocks that are characterized by kerogen type III with TOC of ~ 6.1 wt% and Tmax values of 465 °C, along with Permian–Triassic fluvial–deltaic sandstone reservoir units, with porosity varying from 7 to 18%; and a Bajocian (restricted marine shales) as a seal. Play II has Bajocian restricted marine shale source rocks that are correlated to kerogen type II/III and III Makarawe shales, which have an average TOC of 1.7 w% and Tmax of 450 ℃, and is marked by Middle Jurassic carbonate reservoirs with an average porosity of 15%, capped with mid-Late Jurassic marine shales. Play III is characterized by Campanian shales as source rocks, Early Cretaceous fluvial–deltaic sandstone reservoir with a porosity of 15–20%, and is capped by Late Cretaceous transgressive marine shales. The analyses indicate that plays I and II are particularly more prospective, as manifested by the gas reserves discovered in offshore Songo Songo Island, making a Rufiji Basin a viable potential basin for hydrocarbon generation and accumulation. The findings of this review study support follow up exploration activities and researches, which can ultimately lead to a commercial discovery oil reserves in the basin.
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    Spatial and temporal variations in environmental variables in relation to phytoplankton composition and biomass in coral reef areas around Unguja, Zanzibar, Tanzania
    (Springer, 2015) Samwel Mchele Limbu; Kyewalyanga, M.
    Phytoplankton can indirectly indicate health status of coral reefs due to their sensitivity to changes in water quality parameters. This study explored the spatial and temporal variability in water quality and nutrients in relation to phytoplankton community composition and chlorophyll a concentration at Bawe, Mnemba, Chumbe and Pongwe coral reef sites in Unguja Island. In situ measurements of dissolved oxygen, temperature, salinity and pH were done every month for 1 year. Surface water samples were collected for determination of phytoplankton composition, nutrients and chlorophyll a concentration. Dissolved oxygen, temperature, salinity and pH did not differ significantly among the four sites (p > 0.05) but showed significant temporal variations among months (p < 0.05). Bawe had significantly higher phosphate concentration (1.45 ± 0.57 µg L−1 ) than Chumbe (0.74 ± 0.53 µg L−1), Mnemba (0.42 ± 0.30 µg L−1) and Pongwe (0.28 ± 0.10 µg L−1; p < 0.05). Similarly, Bawe had significantly higher nitrate concentration (0.81 ± 0.43 µg L−1) than Mnemba (0.33 ± 0.14 µg L−1) and Pongwe (0.24 ± 0.13 µg L−1 ; p < 0.05) but similar to Chumbe (0.90 ± 0.35 µg L−1; p > 0.05). However, values obtained at all the studied sites were less than 3 and 14 mg L−1 for phosphate and nitrate, respectively, for eutrophic oceans. Phytoplankton species were dominated by Bacillariophyceae (70.83 %) and some species identified such as Ceratium sp., Dinophysis sp., Protoperidinium sp., Prorocentrum sp., Oscillatoria sp. and Dictyocha fibula are known to produce toxins that affect fish species. Bawe had significantly higher chlorophyll a concentration (0.47 ± 0.07 mg L−1) than Mnemba (0.33 ± 0.04 mg L−1 ) and Chumbe (0.33 ± 0.04 mg L−1; p < 0.05). Chlorophyll a con centration was spatially inversely related to distance from Unguja town (p < 0.05) while it was temporally significantly positively correlated with dissolved oxygen, nitrate and phosphate (p < 0.05). The study revealed that, the coral reef sites have low nutrient levels and are in good health. The existence of toxic phytoplankton species suggests careful consumption of fisheries resources at the four coral reef sites and frequent monitoring for Harmful Algal Blooms (HABs) is required. The higher nutrients and chlorophyll a concentrations at Bawe Island compared to other sites calls for mechanisms to limit the release of domestic sewage from households and hotels to safeguard the coral reefs.
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    Phytoplankton primary production
    (United Nations Environment Programme/Nairobi Convention Secretariat, 2015) Kyewalyanga, Margareth
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    The decline in phytoplankton biomass and prawn catches in the Rufiji-Mafia Channel, Tanzania
    (WIOMSA, 2016) Semba, M.; Kimirei, I.; Kyewalyanga, M.; Peter, N.; Brendonck, L.; Somers, B.
    The world’s oceans have seen significant declines in phytoplankton-the primary food source in the marine environ ment. 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 nar row 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.
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    Variability of Chlorophyll-a in Relation to Physico-Chemical Variables in Zanzibar Coastal Waters
    (SCIENCE SIGNPOST PUBLISHING INC. (SSPub), 2017-12-25) Moto, E.; Kyewalyanga, M.
    The relationships between chlorophyll-a (Chl-a), nutrients and other physico-chemical variables are important for marine water management strategies. In this study, monthly Chlorophyll-a (Chl-a) concentration, temperature, salinity, pH, dissolved oxygen and nutrients were measured at two sites (Bawe and Chwaka Bay) in Zanzibar coastal waters from May 2012 to May 2013. The mean Chl-a concentration ranged from 0.69 mg/m3 to 1.86 mg/m3, with insignificant variation between the sites, and significant differences among the stations being higher in near shore stations than in open seawater stations (t= 5.296, P < 0.0001). The results revealed significant higher Chl-a concentration during the southeast monsoon (SEM) than the northeast monsoon (NEM) (t = 2.871, P < 0.0152). In addition, the results showed that, the concentration was significantly correlated positively with salinity (r = 0.640; p = 0.019) and negatively with NO3 (r = -0.563; p = 0.044). The results of this study suggest that high Chl-a concentration to the near shore station is due to sewage system which influence nutrients concentrations, hence result into high Chl-a concentration. Furthermore, the SEM experienced high Chl-a concentration due to strong winds which bring nutrients to the sea surface which favour growth of phytoplankton hence result into high concentration.
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    Species composition, abundance and distribution of phytoplankton in the coastal waters off Zanzibar Island, Tanzania
    (INTERNATIONAL NETWORK FOR NATURAL SCIENCES, 2018-05-13) Moto, E.; Kyewalyanga, M.; Lyimo, T.; Hamisi, M.
    Species composition, abundance and distribution of phytoplankton were studied in Zanzibar coastal waters for one year (May 2012 - May 2013) at two sites, Bawe and Chwaka Bay. The objective of this study was to quantify the health ecosystem of Zanzibar coastal waters as phytoplankton are good indicator in studying an ecosystem. A total of 260 species belonging to 94 genera and 6 classes were recorded at both sites. The phytoplankton assemblage was dominated by Bacillariophyceae (diatoms) which accounted for 70% of the total phytoplankton. Dinoflagellates ranked second in terms of abundance (24%). Cyanophyceae accounted for 5% of the total phytoplankton and less than 1% of the total standing crop was attributed to chlorophyceae, dictyochophyceae and crysophyceae. Abundant concentrations of diatoms composed mostly of several species which were observed throughout the sampling time which included Chaetoceros sp, Rhizosolenia sp, Thalassiothrix sp, Nitzschia sp, Guinardia sp, Bacteriastrum sp, Pleurosigma sp and Coscinodiscus sp. Diatoms were abundant due to their resilient ability to withstand the varied environmental factors. Some dinoflagellates in low densities were observed at both sites. The highest phytoplankton density was 9189 cells/l, while the lowest density was 2227 cells/l recorded at Bawe and Chwaka Bay, respectively. Southeast monsoon (SEM) season phytoplankton (15244 counts/l) were higher than the Northeast monsoon (NEM) season (13982 counts/ml). Also species diversity was higher during the SEM than the NEM (t =3.155, p = 0.0058). Higher abundance and diversity during SEM might be attributed by low sea surface temperature, higher salinity, sulphate and nitrate levels.
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    Health problems related to algal bloom among seaweed farmers in coastal areas of Tanzania
    (ACADEMIC JOURNAL, 2018-08) Said, A.H.; Msuya, F.E.; Kyewalyanga, M.S.; Mmochi, A.J.; Mwihia, E.W.; Skjerve, E.; Ngowi, H.A.; Lyche, J.L.
    There is a scarcity of research-based data on the factors associated with skin irritation due to algal blooms in seaweed farming. Changes in temperature with an increase in nutrients levels lead to the growth of harmful algal blooms, which produce many active metabolites, some of which induce toxic responses in human including skin irritation. The objective of this study was to identify health problems experienced by seaweed farmers and the seasons when they occur, and how these are treated. A cross sectional study design was used to gather data using structured questionnaire, focus group discussions and key informant interviews. The study was conducted between June and August 2015, in six villages, two from Mainland, and four from Zanzibar Islands, Tanzania. Study revealed that seaweed more than 50% of farmers experienced skin irritation problem, followed by 30.4% who had eye related problems, and only 19.6% had respiratory disorders as the most serious. Hot season, which is associated with algal blooms, was the period with the highest occurrence of skin irritation. No specific medication was used to treat the health problems reported. In some severely affected areas, farmers could not tend to their farms for months, a situation which affected their income. It is suggested that the findings from this study would reduce this knowledge gap and motivate stakeholders especially the policy makers to implement measures, which reduce the health problems observed due to algal blooms in the seaweed farmers.
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    Antioxidants activity of the cyanobacterium, Arthrospira (Spirulina) fusiformis cultivated in a low-cost medium
    (ACADEMIC JOURNAL, 2018-08) Michael, A.; Kyewalyanga, M.S.; Mtolera, M.S.; Lugomela, C.V.
    Spirulina species are known to have a good nutritional profile and antioxidant properties against reactive oxygen species. However, little is known about the antioxidant contents and the scavenging ability of Arthrospira fusiformis, cultivated under various conditions. This study aimed at evaluating the content of antioxidants (total phenols, total flavonoids, β-carotene, and lycopene) and the activity of A.fusiformis produced using low-cost culture (LCMA) and standard culture (Zarrouk) media. The results revealed that A. fusiformis is rich in antioxidants and it possesses high scavenging and chelating activities. Interestingly, the LCMA was superior over the Zarrouk medium as it resulted in spirulina with a higher amount of antioxidants and lower EC50 values. In this context, production of natural antioxidants can be maximized through the use of cost-saving, inorganic culture medium.
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    The influence of physical-chemical variables on the spatial and seasonal variation of Chlorophyll-a in coastal waters of Unguja, Zanzibar, Tanzania
    (WIOMSA, 2018) Peter, N.; Semba, M.; Lugomela, C.; Kyewalyanga, M.S.
    Chlorophyll-a (Chl-a) concentrations were measured at four sites around Unguja, Zanzibar during the northeast (NE) and southeast (SE) monsoon seasons. Data for Chl-a, nitrate, phosphate, ammonia, dissolved oxygen, sea sur face temperature, pH and salinity were collected once a month from March 2008 to March 2009. The SE monsoon had insignificantly higher Chl-a compared to the NE monsoon season when Chl-a for Bawe, Chumbe, Pongwe and Mnemba were combined (W = 234, p = 0.93). The drivers of high Chl-a during the SE monsoon were ammonia and nitrate. Results from individual sites showed that Pongwe and Mnemba had higher median Chl-a during the SE than the NE monsoon season. Temperature, dissolved oxygen and ammonia were the major factors that influenced high Chl-a at these sites. In contrast, Chumbe and Bawe had higher median Chl-a during the NE- than the SE mon soon season. The major factors influencing high Chl-a in the NE at Chumbe and Bawe were high levels of nutrients, mainly from sewage effluent and various human activities around the coast in Zanzibar town. The interaction of Chl-a between monsoon seasons (NE and SE) and sites (Bawe, Chumbe, Pongwe and Mnemba) was insignificant (F(1,3) = 1.3144, p = 0.2949). The principal component analysis revealed that different physical and chemical environmental variables affect Chl-a concentration over time and location.
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    Biomass and nutritive value of Spirulina (Arthrospira fusiformis) cultivated in a cost-effective medium
    (SPRINGER NATURE, 2019-12-23) Michael, A.; Kyewalyanga, M.S.; Lugomela, C.V.
    Introduction Cultivation of spirulina at commercial-scales relies on analytical grade–based media, which are expensive and so are the product. Purpose This study assessed the biomass, proximate composition, and other useful compounds in Spirulina (Arthrospira fusiformis) produced with a cost-effective culture medium (LCMA), and the results were compared with those from a standard Zarrouk medium–grown spirulina. Methods The LCMA medium was formulated by using a commercial NPK10-20-20 fertilizer as a source of the three major nutrients for spirulina growth, and other three ingredients from Zarrouk medium. The experiment was conducted for 28 days in the glass aquaria under indoor conditions. Standard analytical methods were applied for the determination of proximate composition, chlorophyll, minerals, and vitamins in the spirulina biomass. Result The LCMA medium showed the best growth conditions by accumulating higher chlorophyll content (0.99 ± 0.02%) and dry weight (0.75 ± 0.01 g/100 ml) as well as attaining higher optical density (2.06 at day 15) earlier than the Zarrouk medium. The results of the proximate analysis for spirulina cultured in the LCMA medium were of good quality, with the protein contributing more than 50% of its dry matter. It was further noticed that the LCMA was an ideal medium for optimization of vitamins and some minerals since it recorded a significant amount of most of the analyzed vitamins together with the minerals sodium and potassium compared with the Zarrouk medium. Conclusion It is suggested that LCMA medium could be used as the alternative and cheap medium for maximization of biomass and production of useful biochemical compounds in spirulina species.
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    Isolation of the Tephrosia vogelii extract and rotenoids and their toxicity in the RTgill-W1 trout cell line and in zebrafish embryos
    (ELSEVIER, 2020-05-23) Said, A.H.; Solhaug, A.; Sandvik, M.; Msuya, F.E.; Kyewalyanga, M.S.; Mmochi, A.J.; Lyche, J.L.; Hurem, S.
    This study focused on identifying the rotenoids from the Tephrosia vogelli plant (fish-poison-bean), investigating the toxic potency of a crude T. vogelii extract and individual rotenoids (tephrosin, deguelin and rotenone) in vitro and in vivo and assessing the mode of action. A trout (Onychorynhis mykiss) gill epithelial cell line (RTgill-W1) was used to determine the cytotoxicity of rotenoids and effects on cell metabolism. Zebrafish (Danio rerio) aged from 3 h post fertilization (hpf) to 72 hpf were used for testing the developmental toxicity. The crude T. vogelii plant extract significantly decreased the cellular metabolic activity and was cytotoxic at lower concentrations (5 and 10 nM, respectively), while tephrosin, deguelin and rotenone showed these effects at concentrations � 50 nM. The crude T. Vogelli extract had the highest toxic potency and induced adverse health effects in zebrafish including deformities and mortality at the lowest concentration (5 nM) compared to rotenone (10 nM) and deguelin and tephrosin (50 nM). These results indicate that the crude T. Vogelii extracts are highly potent and the bioactivity of these extracts warrant further investigation for their potential use to treat parasites in human and veterinary medicine and as a natural alternative to pesticides.
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    The small pelagic fishery of the Pemba Channel, Tanzania: What we know and what we need to know for management under climate change
    (ELSEVIER, 2020-08-20) Sekadende, B.; Scott, L.; Anderson, J.; Answani, S.; Francis, J.; Jacobs, Z.; Jebri, F.; Jiddawi, N.; Kamukuru, A.T.; Kelly, S.; Kizenga, H.; Kuguru, B.; Kyewalyanga, M.; Noyon, M.; Nyandwi, N.; Painter, S.C.; Palmer, M.; Raitsos, D.E.; Roberts, M.; Sailley, S.F.; Samoilys, M.; Saur, W.H.H.; Shayo, S.; Shaghude, Y.; Tailor, S.F.W.; Wihsgott, J.; Popova, E.
    Small pelagic fish, including anchovies, sardines and sardinellas, mackerels, capelin, hilsa, sprats and herrings, are distributed widely, from the tropics to the far north Atlantic Ocean and to the southern oceans off Chile and South Africa. They are most abundant in the highly productive major eastern boundary upwelling systems and are characterised by significant natural variations in biomass. Overall, small pelagic fisheries represent about one third of global fish landings although a large proportion of the catch is processed into animal feeds. Nonetheless, in some developing countries in addition to their economic value, small pelagic fisheries also make an important contribution to human diets and the food security of many low-income households. Such is the case for many communities in the Zanzibar Archipelago and on mainland Tanzania in the Western Indian Ocean. Of great concern in this region, as elsewhere, is the potential impact of climate change on marine and coastal ecosystems in general, and on small pelagic fisheries in particular. This paper describes data and information available on Tanzania's small pelagic fisheries, including catch and effort, management protocols and socio-economic significance. Then, incorporating the rapidly improving understanding of the region's oceanography resulting from the application of remote sensing and oceanographic modelling, the paper undertakes the most complete assessment to date of the potential impacts of climate change on the small pelagic fishery of the Pemba Channel. Pathways of climate change impact are explored and crucial knowledge gaps, both in terms of the fishery itself and the wider ecosystem, are identified in order to guide future research activities. Although we analyse small pelagics in the specific context of the Pemba Channel, the key challenges identified in the analysis are likely to be relevant to many small pelagic fisheries in coastal nations heavily dependent on living marine resources.
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    Variability of Mackerel fish catch and remotely-sensed biophysical control in the eastern Pemba Channel
    (ELSEVIER, 2021-03-11) Kizenga, H.J.; Jebri, F.; Shaghude, Y.; Raitsos, D.E.; Srokosz, M.; Jacobs, Z.L.; Nencioli, F.; Shalli, M.; Kyewalyanga, M.S.; Popova, E.
    Advances in satellite remote sensing of environmental perturbations have become important in understanding variations of ocean productivity and small pelagic fish catches. This marine resource is vital for coastal populations dependent on artisanal fishing for their income and food security, such as in coastal East Africa. In this region, the eastern Pemba Channel (Tanzania) represents a hotspot area, for a variety of marine species including small pelagics and coral reef associated species. This study examines the links between mackerel fish catch, one of the important small pelagic fish for direct consumption in the region, and changes in environmental oceanographic parameters over the period 2012–2018. The fisheries catch data is a rare local dataset, consisting of daily mackerel landings (from 2012 onwards) and supplemented by qualitative information on the mackerel fishery obtained through interviews with local stakeholders. The physical factors influencing phytoplankton biomass, and in turn, mackerel fisheries yield is investigated, using remotely-sensed chlorophyll-a (Chl-a) and Sea Surface Temperature (SST), together with Mixed Layer Depth (MLD) data from the high-resolution ocean model NEMO. We show that seasonal variations in mackerel landings are positively (negatively) correlated with Chl-a (SST) with a 1-month time lag (i.e., biophysical factors change first, mackerel stocks follow one month later). On the eastern side of the Pemba Channel, cooler SST and higher Chl-a are observed during the Southeast monsoon accompanied by increased mackerel landings, suggestive of enhanced productivity. Interannually, these relationships remain valid both for monthly and annual means, which confirms the close link between the variations of mackerel and biophysical conditions. Analysis of the Chl-a and MLD anomalies, relative to the mean, reveals that the phytoplankton blooms observed on the eastern side of the Pemba Channel, during the Southeast monsoon, are likely due to the deepening of the mixed layer, which tends to entrain cold and nutrient rich waters from greater depths to the surface. We conclude that upper ocean mixing contributes to the observed enhanced productivity along with other environmental factors. Additionally, we show how our results can be applied in the management of the mackerel resource in the Pemba Channel.
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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.
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    Evidence of localised upwelling in Pemba Channel (Tanzania) during the southeast monsoon
    (ELSEVIER, 2020-12-07) Painter, S.C.; Sekadende, B.; Michael, A.; Noyon, M.; Shayo, S.; Godfrey, B.; Mwadini, M.; Kyewalyanga, M.
    Oceanographic and biogeochemical observations collected in Pemba Channel, a deep-water (800 m) channel separating Pemba Island from mainland Tanzania, during the South East monsoon indicate the presence of active upwelling along the western edge of Pemba Island. Surface salinity values, nutrient concentrations and the presence of coccolithophore species previously reported from the mid to lower euphotic zone all suggest up welling from at least 80–100 m depth. The surface waters of the channel were characterised with low NO3 − :PO4 3− (0.68:1) and NO3 − :Si (0.04:1) ratios far below the Brzezinski-Redfield ratio indicating the presence of N-limitation and the possibility that these waters may be susceptible to anthropogenic N inputs. Surface NO3 − concentrations averaged 0.09 ± 0.10 μmol L− 1 but increased to 0.5 μmol L− 1 in the centre of upwelling where coincidentally both integrated nutrient concentrations and surface POC/PON pools were approximately 2-fold higher than the channel average. Despite its significance for local productivity upwelling is tentatively estimated, via stoichio metric assumptions, to enhance local productivity by only 20%. The modest productivity response to upwelling may be explained by picoplankton (0.2–2 μm) dominance of the phytoplankton community with this size-class representing ~80% of total chlorophyll-a. Nevertheless, important spatial variability was identified in larger size fractions and supported by taxonomic analyses with indications that the distribution of Chaetoceros spp. alone may be particularly relevant for understanding the variability in larger (>20 μm) chlorophyll-a size fractions. The location of upwelling has previously been shown to host large concentrations of small pelagic fish thus management of this regionally important resource would benefit from additional investigation of the underlying physical mechanism driving upwelling and subsequently how trophic interactions and ecosystem productivity are influenced.
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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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    Supplementing wastewater with NPK fertilizer as a cheap source of nutrients in cultivating live food (Chlorella vulgaris)
    (SPRINGER NATURE, 2021) Mtaki, Kulwa; Kyewalyanga, Margareth S.; Mtolera, Matern S.P.
    Introduction: The decline in fishery resources from the wild has led to an ever increasing focus on aquaculture in recent years. With increasing aquaculture of animal species, there is an increasing need for suitable microalgae in the production of these animals. However, cultivation of microalgae in expensive pure chemical media is one of the major challenges facing large-scale cultivation of microalgae. Purpose: The present study investigated the suitability of aquaculture wastewater (AWW) supplemented with NPK (nitrogen:phosphorus:potassium) fertilizer as a cheap source of nutrient to cultivate a microalga Chlorella vulgaris (C. vulgaris). Methods: C. vulgaris with an initial cell density of 0.8 × 106 cells/mL was batch cultured in AWW supplemented with NPK at 0.1, 0.5, 1.0 g/L and BBM for 20 days under laboratory conditions using 2000 mL Erlenmeyer flasks. The proximate composition, chlorophyll, minerals, and vitamins analysis of C. vulgaris biomass were done using standard analytical methods. Results: The highest values in optical density (4.872 ± 0.025), dry cell weight (2.858 ± 0.015 g/L), specific growth rate (0.2097 ± 0.0038 day–1), and biomass productivity (0.1701 ± 0.0007 g/L/day) were obtained in C. vulgaris grown in AWW + 1.0 NPK medium. The total chlorophyll, protein, lipid, and carbohydrate content of the microalgae biomass were in the range of 0.05–0.862%, 44.062–57.089%, 17.064–23.260%, and 15.217–21.896%, respectively. Furthermore, microalgae grown in AWW + 1.0 NPK showed good vitamin and mineral content compared to BBM grown alga. Conclusion: These findings indicated that the AWW + 0.1 NPK, AWW + 0.5 NPK, and AWW + 1.0 NPK are potential growth media for C. vulgaris cultivation and can replace the BBM medium, which is very expensive and less accessible to users.
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    Assessment of Antioxidant Contents and Free Radical-Scavenging Capacity of Chlorella vulgaris Cultivated in Low Cost Media
    (MDPI, 2020-12) Mtaki, Kulwa; Kyewalyanga, Margareth Serapio; Mtolera, Matern S.P.
    The current study assessed antioxidants contents (total phenolics and total flavanoids, β-carotene and lycopene) present in Chlorella vulgaris (C. vulgaris) cultivated in low cost media and their free radical scavenging activities. Microalgae was cultured using Bold basal medium (BBM) as a control, 5% banana stem compost (BCM) and aquaculture wastewater supplemented with 1.0 g/L NPK (ANM). The free radical scavenging ability was analysed using 1,1-diphenyl-2-picrylhydrazyl assay. Cells grown on BCM resulted in higher (13.73 ± 0.121%) extraction yield than in other media. The phenolic (8.53 ± 0.10 mg/g GAE) and lycopene (0.29 ± 0.008 mg/g) content were highest in cells grown on BCM and BBM, respectively. Microalgae cultured in ANM displayed higher (547.023 ± 34.703 mg/g RE) flavanoid and β-carotene (2.887 ± 0.121 mg/g) content than in other media. Furthermore, cells cultivated in BCM showed highest (97.87 ± 0.088%) scavenging activity than in BBM. These results indicated that the BCM and ANM can be used as alternative to expensive synthetic media for antioxidant production in C. vulgaris.