Browsing by Author "Mamboya, Florence"
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Item Academic Journals Food Preference of the Sea Urchin Tripneustes Gratilla (Linnaeus, 1758) In Tropical Seagrass Habitats at Dar Es Salaam, Tanzania(2010-12) Lyimo, Thomas J.; Mamboya, Florence; Hamisi, Mariam; Lugomela, CharlesThe sea urchin Tripneustes gratilla is the most well-known seagrass grazer in the Western Indian Ocean and a few cases of overgrazing have been reported. However, few studies on their feeding preference have been performed in this region. In this study, the food items in the gut contents of T. gratilla collected from seagrass beds and in a bare sediment in intertidal areas of Dar es Salaam, Tanzania, were analysed and compared to their availability in the surrounding environment. A total of 59 micro and macro-algae species were identified from the environment and the guts of T. gratilla, of which 48 were found in both gut contents and the environment. Gut contents of T. gratilla collected from mono specific seagrass habitats were dominated by the species in which they were found. In a mixture of four different seagrass species, Syringodium isoetifolium was preferred (with electivity indices (E*) of +0.36) while Cymodocea rotundata, Halodule uninervis and Thalassia hemprichii were slightly avoided (E* = -0.24, -0.22 and -0.22, respectively). We concluded that T. gratilla generally feeds on available seagrass species. However, in the presence of different types of seagrasses it showed preference to S. isoetifolium possibly due to presence of high epiphyte load which may increase its palatability.Item Accumulation of Copper and Zinc and their Effects on Growth and Maximum Quantum Yield of the Brown Macroalga Padina Gymnospora(2008) Mamboya, Florence; Pratap, Harish B.; Mtolera, M.; Björk, MatsAccumulation and the effects of copper and zinc on the macroalga Padina gymnospora were assessed in the laboratory after artificial exposure to copper and zinc (separately or in combination). Exposure concentrations of copper used were 0, 25, 50, 100, 500 and 1,000 µg l-1. Concentrations of zinc exposure were 0, 50, 100, 250, 1,000 and 5,000 µg l-1. The simultaneous (or combined) addition of copper and zinc (Cu+Zn) involved 25+50, 50+100, 100+250, and 500+1,000 µg l-1. Accumulation patterns were determined by measuring tissue contents of copper and zinc, while the tolerance was assessed by measuring growth rate and photosynthetic performance, as maximum quantum yield (Fv/Fm). Furthermore, the influence of major nutrients (phosphates and nitrates) on algal-metal-accumulation was estimated after additions of nitrate (1, 10 and 20 mg l-1) and phosphate (0.1, 1 and 2 mg l-1). The data obtained showed that the accumulation increased linearly with the increase in metal concentration in the growth media. However, the presence of additional nitrate and phosphate reduced both the metal accumulation and their toxic effects. Both algal growth rate and maximum quantum yields were negatively affected in proportion to the increase in metal concentrations and exposure time. At exposures to 50, 100 and 500 µg l-1 copper, inhibition in growth was greater than 50%, while an exposure to 1,000 µg l-1of zinc was needed to cause the same effect on growth and Fv/Fm. Growth rate was a more sensitive indicator of stress than maximum quantum yield in response to exposure to copper and zinc Accumulation of Copper and Zinc and their Effects on Growth and Maximum Quantum Yield of the Brown Macroalga Padina GymnosporaItem Food Preference of the Sea Urchin Tripneustes Gratilla (Linnaeus, 1758) In Tropical Seagrass Habitats at Dar Es Salaam, Tanzania(2011) Lyimo, Thomas J.; Mamboya, Florence; Hamisi, Mariam; Lugomela, CharlesThe sea urchin Tripneustes gratilla is the most well-known seagrass grazer in the Western Indian Ocean and a few cases of overgrazing have been reported. However, few studies on their feeding preference have been performed in this region. In this study, the food items in the gut contents of T. gratilla collected from seagrass beds and in a bare sediment in intertidal areas of Dar es Salaam, Tanzania, were analysed and compared to their availability in the surrounding environment. A total of 59 micro and macro-algae species were identified from the environment and the guts of T. gratilla, of which 48 were found in both gut contents and the environment. Gut contents of T. gratilla collected from mono specific seagrass habitats were dominated by the species in which they were found. In a mixture of four different seagrass species, Syringodium isoetifolium was preferred (with electivity indices (E*) of +0.36) while Cymodocea rotundata, Halodule uninervis and Thalassia hemprichii were slightly avoided (E* = - 0.24, -0.22 and -0.22, respectively). We concluded that T. gratilla generally feeds on available seagrass species. However, in the presence of different types of seagrasses it showed preference to S. isoetifolium possibly due to presence of high epiphyte load which may increase its palatability.Item Influence of Combined Changes in Salinity and Copper Modulation on Growth and Copper Uptake in The Tropical Green Macroalga Ulva Reticulate. Estuar Coast Shelfs(Elsevier, 2009-08) Mamboya, Florence; Lyimo, Thomas J.; Landberg, Tommy; Björk, MatsThe influence of salinity on growth and Cu uptake in the green macroalga Ulva reticulata collected from the intertidal area in the Western Indian Ocean was studied under controlled laboratory conditions. Exposure concentrations ranged from 5 to 500 μg Cu l−1 at five salinities (ranging 20–40). The accumulation of Cu increased with decreasing salinity, so that the uptake at 500 μg Cu l−1 was approximately 2.7, 2.4 and 2.0 times higher at salinities of 20, 25, and 30 respectively, than uptake at salinity of 35, and with uptake being lowest at salinity of 40. Ulva maintained a positive growth rate over the whole salinity range (20–40), with highest rates at salinity of 35. When exposing to Cu at low salinities (20 and 25), the growth rate of Ulva was strongly inhibited suggesting an increase in toxicity of Cu with decreasing salinity. EC50 and NOEC increased with increase in salinity, implying a reduced Cu toxicity at high salinities. It was concluded that salinity needs to be considered when using macroalgae, such as U. reticulata, as a bioindicator of heavy metals in areas with heavy rainfall, underground fresh water intrusion or in estuaries, asItem Seagrass - Sea urchin interaction in shallow littoral zones of Dar es Salaam, Tanzania(Wiley Online Library, 2008-07) Mamboya, Florence; Lugomela, Charles; Mvungi, Esther F.; Hamisi, Mariam; Kamukuru, Albogast T.; Lyimo, Thomas J.Seagrasses biomass, canopy height, shoot density, percentage cover, and sea urchin abundance wereintermittently (between July and November 2007) studied at four littoral sites in the Dar es Salaam area(Mjimwema, Mbweni, Bongoyo Island and Mbudya Island) in order to investigate the seagrass–sea urchinassociation.2. Seagrass biomass ranged from 126.7765.62 g dwt m2in the upper sub-tidal area at Bongoyo Island to508.17133.4 g dwt m2in the upper sub-littoral area at Mbudya Island. Canopy height ranged from6.5172.76 cm in the mid-littoral zone at Mjimwema to 23.878.93 cm in the upper sub-littoral zone atMbudya Island. Shoot densities ranged from 363.67268.9 shoots m2in the mid-littoral zone at Mjimwema to744.07466.9 shoots m2in the lower littoral zone at Mbudya Island.3. Seagrass biomass, canopy height and percentage cover differed significantly among study sites (P 5 0.001,0.0001, 0.008 respectively). However, there was no significant difference in shoot density among the sites(P 5 0.376).4. Ten species of sea urchins were recorded, Echinometra mathaei being the most abundant followed byTripneustes gratilla. Total sea urchin abundance was significantly different among the study sites (P 5 0.001).Seagrass–sea urchin interaction was depicted by significant negative correlations between sea urchin densitieswith seagrass biomass, canopy height, shoot density and percentage cover. This suggests that grazing by seaurchins might have contributed to the reduction of above ground seagrass biomass in locations with higher seaurchin densities. However, further studies are required to corroborate the present results and assess effects ofother factors (e.g. light, nutrients and currents), which also influence seagrass growth.Item Seagrass - Sea Urchin Interaction in Shallow Littoral Zones of Dar es Salaam, Tanzania(Wiley, 2009-06) Mamboya, Florence; Lugomela, Charles; Mvungi, Esther; Hamisi, Mariam; Kamukuru, Albogast T.; Lyimo, Thomas J..Seagrasses biomass, canopy height, shoot density, percentage cover, and sea urchin abundance were intermittently (between July and November 2007) studied at four littoral sites in the Dar es Salaam area (Mjimwema, Mbweni, Bongoyo Island and Mbudya Island) in order to investigate the seagrass–sea urchin association.2.Seagrass biomass ranged from 126.7±65.62 g dwt m−2 in the upper sub-tidal area at Bongoyo Island to 508.1±133.4 g dwt m−2 in the upper sub-littoral area at Mbudya Island. Canopy height ranged from 6.51±2.76 cm in the mid-littoral zone at Mjimwema to 23.8±8.93 cm in the upper sub-littoral zone at Mbudya Island. Shoot densities ranged from 363.6±268.9 shoots m−2 in the mid-littoral zone at Mjimwema to 744.0±466.9 shoots m−2 in the lower littoral zone at Mbudya Island.3.Seagrass biomass, canopy height and percentage cover differed significantly among study sites (P=0.001, 0.0001, 0.008 respectively). However, there was no significant difference in shoot density among the sites (P=0.376).4.Ten species of sea urchins were recorded, Echinometra mathaei being the most abundant followed by Tripneustes gratilla. Total sea urchin abundance was significantly different among the study sites (P=0.001). Seagrass–sea urchin interaction was depicted by significant negative correlations between sea urchin densities with seagrass biomass, canopy height, shoot density and percentage cover. This suggests that grazing by sea urchins might have contributed to the reduction of above ground seagrass biomass in locations with higher sea urchin densities. However, further studies are required to corroborate the present results and assess effects of other factors (e.g. light, nutrients and currents), which also influence seagrass growth. Copyright © 2009 John Wiley & Sons, Ltd.Item Seagrass - Sea urchin interaction in shallow littoral zones of Dar es Salaam, Tanzania(Wiley, 2009) Mamboya, Florence; Lugomela, Charles; Mvungi, Esther; Hamisi, Mariam; Kamukuru, Albogast T.; Lyimo, Thomas J.Seagrasses biomass, canopy height, shoot density, percentage cover, and sea urchin abundance wereintermittently (between July and November 2007) studied at four littoral sites in the Dar es Salaam area(Mjimwema, Mbweni, Bongoyo Island and Mbudya Island) in order to investigate the seagrass–sea urchinassociation.2. Seagrass biomass ranged from 126.7765.62 g dwt m2in the upper sub-tidal area at Bongoyo Island to508.17133.4 g dwt m2in the upper sub-littoral area at Mbudya Island. Canopy height ranged from6.5172.76 cm in the mid-littoral zone at Mjimwema to 23.878.93 cm in the upper sub-littoral zone atMbudya Island. Shoot densities ranged from 363.67268.9 shoots m2in the mid-littoral zone at Mjimwema to744.07466.9 shoots m2in the lower littoral zone at Mbudya Island.3. Seagrass biomass, canopy height and percentage cover differed significantly among study sites (P 5 0.001,0.0001, 0.008 respectively). However, there was no significant difference in shoot density among the sites(P 5 0.376).4. Ten species of sea urchins were recorded, Echinometra mathaei being the most abundant followed byTripneustes gratilla. Total sea urchin abundance was significantly different among the study sites (P 5 0.001).Seagrass–sea urchin interaction was depicted by significant negative correlations between sea urchin densitieswith seagrass biomass, canopy height, shoot density and percentage cover. This suggests that grazing by seaurchins might have contributed to the reduction of above ground seagrass biomass in locations with higher seaurchin densities. However, further studies are required to corroborate the present results and assess effects ofother factors (e.g. light, nutrients and currents), which also influence seagrass growth.Item Short-Term Effects of Three Herbicides on the Maximum Quantum Yield and Electron Transport Rate of Tropical Seagrass Thalassodendron ciliatum(Elsevier, 2011-12) Wahedally, Shalena F.; Mamboya, Florence; Lyimo, Thomas J.; Bhikajee, Mitrasen; Björk, MatsThis article describes the laboratory findings of the short-term effects of three herbicides on the tropical seagrass Thalassodendron ciliatum. For three days T. ciliatum was exposed to Diuron, Fusillade (Forte) and 2, 4-D amine, either individually or in combination. The toxic effects were investigated by measuring the effective quantum yield through rapid light curves and the maximum quantum yield (Fv/Fm), before and after exposure at intervals of 2, 4, 6, 8, 24, 48 and 72 hrs. During the recovery phase both Fv/Fm and effective quantum yield were measured after 2, 4, 6, 8, 24, 48 and 72 hrs. Results revealed an inhibition of both ETRmax and Fv/Fm after diuron exposure. No effect on ETRmax and Fv/Fm were observed when T. ciliatum was exposed to Fusilade Forte and 2, 4-D amine. Any combination of the herbicides that involved Diuron showed inhibition both in ETRmax and Fv/Fm. Exposure to a combination of Fusilade Forte and 2,4-D amine had no effect on both ETRmax and Fv/Fm of T. ciliatum. It is concluded that, diuron is toxic to T. ciliatum at a concentration which can be found in a polluted environment while the other herbicides did not show inhibition of the parameters measured. K E Y W O RDS: Thalossodendron ciliatum, herbicides, toxicity, Fucilade, 2,4-D amine I N T R O D U C T I O N Seagrasses are among the most productive ecosystems in the shallow water marine envi-ronment. It provides habitat to a number of flora and fauna species and stabilises the sediments. Its survival is both of ecological and economic-al importance. The decline of seagrass in the past decade has mainly been attributed to anthropogenic activities. Excessive input of nutrients in the seawater has lead to an increase in epiphytic load on the seagrass that ultimately reduces light (Walker et al., 1999). Other factors in some areas may also contribute to the fast decline of seagrass. One of these can be the impact of the agricultural activities that involve utilisation of large amounts of herbicides that can leak into the seawater through runoff water or ground water seepage. For example, in Northern Queensland diuron herbicide was detected in seagrass tissue and sediments (Hynes, et al., 1998). A serious risk posed to the marine environment is the fast growing developmental activities along the coastal regions in most developing countries bordering the Western Indian Ocean. Also agricultural activities along