Research Repository :: Browsing by Author "Kyewalyanga, M."

Browsing by Author "Kyewalyanga, M."

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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.
The Development of a Scientific Forum in the Western Indian Ocean Region
(1998) Kyewalyanga, M.; Francis, Julius; Johnstone, Ron W.
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.
Existence of Potentially Harmful Microalgae in Coastal Waters around Zanzibar: A Need for a Monitoring Programme?
(1999) Kyewalyanga, M.; Lugomela, Charles
A nine-month survey of potentially harmful microalgae was carried out in the coastal waters around Unguja Island, Zanzibar, from September 1998 to June 1999. Using a light microscope, more than 20 species were identified. These were distributed among three major microalgal groups: the cyanobacteria, mostly dominated by Trichodesmium spp; the dinoflagellates, dominated by Prorocentrum spp. and Gambierdiscus toxicus; and the diatoms, mostly Pseudo-nitzschia spp. This and other preliminary studies indicate the presence of harmful microalgae in Zanzibar waters. Further studies to assess both spatial and temporal distribution, as well as potential ecologic and economic effects, are recommended.
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.
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.
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.
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.

Browsing by Author "Kyewalyanga, M."

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