Browsing by Author "Mvungi, Esther"

Now showing 1 - 3 of 3
  • Thumbnail Image
    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.
  • Thumbnail Image
    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 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.
  • Thumbnail Image
    Item
    When Zostera Marina is Intermixed With Ulva, Its Photosynthesis is Reduced by Increased Ph and Lower Light, but not by Changes in Light Quality
    (Elsevier, 2012-09) Mvungi, Esther; Lyimo, Thomas J.; Björk, Mats
    To evaluate the effects of Ulva on the photosynthetic capacities of the temperate seagrass Zostera marina,we compared it in the laboratory under normal light and light filtered through layers of Ulva intesti-nalis, and repeated the experiments with the addition of pH-induced changes in carbon speciation andavailability. One thallus of Ulva reduced photosynthetically available irradiance to underlying seagrassby about 50% and shifted the quality of remaining light towards the green part of the spectrum (approx-imately 520–570 nm). There was no significant difference in photosynthetic performance between Z.marina under normal light and under Ulva-filtered light when adjusted to the same irradiance as for thecontrol plants, indicating that the green spectrum transmitted through Ulva layers was being absorbedby the seagrass and was as efficient in driving photosynthesis as was the normal light. On the otherhand, algae-generated pH shifts which could extend up to pH 10 had significant negative effects onphotosynthesis of the seagrass, reducing the electron transport rates with up to 75%