Browsing by Author "Hamisi, Mariam"

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    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, Charles
    The 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.
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    Cyanobacterial Occurrence and Diversity in Seagrass Meadows in Coastal Tanzania
    (2007) Hamisi, Mariam; Lyimo, Thomas J.; Muruke, Masoud S. H.
    We report on the occurrence and diversity of cyanobacteria in intertidal seagrass meadows at Ocean Road and Mjimwema, Dar es Salaam, Tanzania. Nutrients, temperature and salinity were measured as comparative environmental factors. A total of 19 different cyanobacteria taxa were encountered, out of which eight were found exclusively in Mjimwema, four exclusively in Ocean Road and seven were common to both sites. Oscillatoria, Lyngbya and Spirulina were the dominant cyanobacterial genera. Cyanobacterial coverage was higher in Mjimwema (31–100%) than in Ocean Road (0–60%). The levels of nutrients in tidal pool waters at Ocean Road ranged from 0.45–1.03 μmol NO3 -N/l, 0.19–0.27 μmol NO2 -N/l and 0.03–0.09 μmol PO4 -P/l. At Mjimwema the nutrient concentration ranges were 0.14–0.93 μmol NO3 -N/l, 0.20–0.30 μmol NO2 -N/l and 0.01-0.07 μmol PO4 -P/l . The nutrient levels were significantly higher at Ocean Road than at Mjimwema (P = 0.001 for nitrate and P = 0.025 for phosphate). There was no significant difference in nitrite levels between the study sites (P = 0.83). The low cyanobacterial diversity and coverage in Ocean Road is related to the high levels of nutrients and physical disturbance from sewage discharge and the harbour in the area.
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    Epiphytic Cyanobacteria of the Seagrass Cymodocea Rotundata: Diversity, Diel Nifh Expression and Nitrogenase Activity
    (Wiley, 2013-05) Hamisi, Mariam; Diez, Beatriz; Lyimo, Thomas J.; Ininbergs, Karolina; Bergman, Birgitta
    Epiphytic cyanobacteria of the seagrass Cymodocearotundata: diversity, diel nifH expression andnitrogenase activityMariam Hamisi,1* Beatriz Díez,2†Thomas Lyimo,3Karolina Ininbergs2and Birgitta Bergman21College of Natural & Mathematical Sciences, TheUniversity of Dodoma, P.O. Box 338, Dodoma,Tanzania.2Department of Ecology, Environment and PlantSciences, Stockholm University, Lilla Frescati, SE-10691 Stockholm, Sweden.3Department of Molecular Biology & Biotechnology, Dares Salaam University, P.O. Box 35179, Dar es Salaam,Tanzania.SummarySeagrasses are photoautotrophic, ecologically im-portant components of many globally widespreadcoastal ecosystems, in which combined nitrogen maylimit their production. We examined the biodiversityand diazotrophic capacity of microbial epiphytesassociated with the phyllosphere of the seagrassCymodocea rotundata of the Western Indian Ocean.Light microscopy, 16S rRNA and nifH gene analysisrevealed the dominance of cyanobacteria in the epi-phytic microbial community. Most phylotypes wererelated to free-living uncultured benthic cyanobacte-ria, while some to cyanobacterial endosymbionts ofmarine diatoms. Novel and potentially diazotrophicspecies, some of known pantropical distribution,were also discovered. Significant diel nitrogenaseactivities (acetylene reduction assay) were recorded(up to 358 ⫾ 232 nmol C2H4g-1of seagrass FW h-1).The nifH gene expression patterns showed that het-erocystous phylotypes may be the dominant diazo-trophs during the day and non-heterocystous atnight. These data show that C. rotundata is colonizedby diverse diazotrophic cyanobacteria species andsuggest that these may be beneficial partners of
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    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, Charles
    The 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.
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    Nitrogen Fixation by Epiphytic and Epibenthic Diazotrophs Associated with Seagrass Meadows along the Tanzanian Coast, Western Indian Ocean. Aquat Microb Ecol
    (2009-09) Hamisi, Mariam; Lyimo, Thomas J.; Muruke, M . H. S.; Bergman, Birgitta
    Seasonal, diurnal, and age-dependent variations in nitrogen fixation (nitrogenase activity) by epiphytic diazotrophs colonizing the seagrasses Halodule uninervis, Cymodocea rotundata, Thalassodendron ciliatum, and Thalassia hemprichii, and by epibenthic diazotrophs associated with seagrass-vegetated and nonvegetated sediments, were estimated at 2 sites along the Tanzanian coast, Western Indian Ocean. Acetylene reduction-gas chromatography showed that nitrogenase activity values were significantly higher (p = 0.0004) at the site with low nutrient levels (Mjimwema) than at the site with higher nutrient levels (Ocean Road). The nitrogenase activity ranged from 10 to 192 nmol N g(-1) h(-1) for H. uninervis, 7 to 80 nmol N g(-1) h(-1) for C. rotundata, 10 to 75 nmol N g(-1)h(-1) for Thalassia hemprichii, and from 4 to 61 nmol N g(-1) h(-1) for Thalassodendron ciliatum. Nitrogenase activity values in sediments covered by seagrasses were significantly higher than in surrounding nonvegetated sediments (t = 4.021, p = 0.0005). Significant variations in nitrogenase activity were apparent depending on leaf age and season, with highest activity being found in mid-aged leaves during the northeastern monsoon (NEM), and in older leaves during the southeastern monsoon (SEM). Daytime nitrogenase activity was appreciable on above-ground seagrass parts, while rhizosphere activity peaked at night-time. Collectively our data show that diazotrophs (cyanobacteria and other bacteria) are associated with seagrasses (leaves and roots), and potentially constitute an integral part of the ecosystem. They show highly dynamic nitrogenase activity and a succession in seagrass colonization, and we concluded that their presence may contribute to the productivity of the seagrass beds.
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    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 m2in the upper sub-tidal area at Bongoyo Island to508.17133.4 g dwt m2in 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 m2in the mid-littoral zone at Mjimwema to744.07466.9 shoots m2in 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.
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    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 m2in the upper sub-tidal area at Bongoyo Island to508.17133.4 g dwt m2in 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 m2in the mid-littoral zone at Mjimwema to744.07466.9 shoots m2in 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.
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    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.