Department of Botany

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Browsing Department of Botany by Author "Björk, Mats"

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    Seagrass Biomass and Productivity in Seaweed and Non-Seaweed Farming Areas in the East Coast of Zanzibar
    (Western Indian Ocean Journal of Marine Science, 2006-01) Lyimo, Thomas J.; Mvungi, Esther F.; Lugomela, Charles K.; Björk, Mats
    Seagrass beds are often subjected to stress resulting from natural and human activities. In this study, the shoot density, biomass and growth characteristics of Thalassia hemprichii and Enhalus acoroides were measured to assess the impact of seaweed farming activities on seagrass meadows at Marumbi, Chwaka Bay and Jambiani in the East Coast of Zanzibar. There was significantly higher T. hemprichii shoot density in non-seaweed areas compared to seaweed farmed areas. However, there were no significant differences in E. acoroides shoot density between seaweed and non-seaweed areas and between the two sites. Also, there was significantly higher total biomass of T. hemprichii in non-seaweed areas compared to seaweed areas. However, there were no significant differences in the total biomass of E. acoroides between seaweed and non-seaweed areas and among the sites. The growth and photosynthetic (ETR and Fv/Fm ratios) characteristics of both T. hemprichii and E. acoroides varied inconsistently between seaweed and non seaweed areas suggesting that there is no effect on seaweed farming to the growth rate of the seagrasses. Thus, the reduced seagrass shoot density and biomass in seaweed farms compared to non-seaweed areas observed in this particular study is most likely to be due to physical disturbances in the farms such as bioturbation or deliberate removal of seagrasses by farmers.
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    When Zostera marina is Intermixed with Ulva, its Photosynthesis is Reduced by increased pH and Lower light, but not by changes in Light Quality
    (2012-09) Mvungi, Esther F.; 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%