Seagrass - Sea urchin interaction in shallow littoral zones of Dar es Salaam, Tanzania
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Date
2008-07
Journal Title
Journal ISSN
Volume Title
Publisher
Wiley Online Library
Abstract
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.
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Keywords
Seagrass biomass, Canopy height, Shoot density, Sea urchin abundance, Tanzania
Citation
Mamboya, F., Lugomela, C., Mvungi, E., Hamisi, M., Kamukuru, A.T. and Lyimo, T.J., 2009. Seagrass–sea urchin interaction in shallow littoral zones of Dar es Salaam, Tanzania. Aquatic Conservation: Marine and Freshwater Ecosystems, 19(S1), pp.S19-S26.