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Water, Salt and Stoichiometrically linked nutrient budget for Chwaka Bay, Tanzania

Tue, 01 Jan 2002 00:00:00 GMT

Title: Water, Salt and Stoichiometrically linked nutrient budget for Chwaka Bay, Tanzania Authors: Ngusaru, A.S.; Mohammed, M.S. Abstract: The water and salt balance at Chwaka Bay in Zanzibar, Tanzania suggests that in order to balance the inflow and outflow of water, there must be a net flux of water from the bay to the open ocean during both the dry and wet seasons. The corresponding salt residual fluxes indicate advective salt export. However, exchange between the bay water with the open ocean replaces this exported salt via mixing. The freshwater residence times at Chwaka Bay are 24 days for dry and 37 days for wet season. The budgets for non-conservative materials indicate a net dissolved inorganic phosphorous (DIP) and dissolved inorganic nitrogen (DIN) flux from the bay to the ocean during wet season. The calculated DIPsyst and DINsyst suggest that the bay acts as a DIP and DIN source during the wet season. Stoichiometry calculations suggest that (p-r) is negative, indicating that Chwaka Bay is net heterotrophic during wet season. The inner bay seems to have net denitrification, but the outer bay seems to be fixing nitrogen at a slower rate. However, the entire bay appears to balance nitrogen fixing and denitrification. Description: Research Group: University of Dar es Salaam, Institute of Marine Sciences, P.O. Box 668, Zanzibar, Tanzania

Variability of Western Indian Ocean currents

Tue, 01 Jan 2002 00:00:00 GMT

Title: Variability of Western Indian Ocean currents Authors: Benny, P.N. Abstract: In the study reported, an attempt was made to understand the intra-annual variability of the western Indian Ocean circulation by estimating the monthly dynamic topography with respect to 400db. The major currents in the western Indian Ocean are clearly depicted in the topography. Among the currents, the Somali Current exhibits strong annual variability. Eddy circulation is prominent in the northern part of the Somali Current during the southwest monsoon period. Seasonal variability is also noticed in the North Equatorial Current. Slight spatial and temporal changes are noticed in the South Equatorial Current and Equatorial Counter Current. The Equatorial Jet flow occurs in the monsoon transition periods of May and November between the equator and 3° South. Description: Research Group: Department of Physical Oceanography, Cochin University of Science & Technology, Cochin, India 682016

Ulva reticulata and Gracilaria crassa: Macroalgae That Can Biofilter Effluent from Tidal Fishponds in Tanzania

Tue, 01 Jan 2002 00:00:00 GMT

Title: Ulva reticulata and Gracilaria crassa: Macroalgae That Can Biofilter Effluent from Tidal Fishponds in Tanzania Authors: Msuya, F.E.; Neori, A. Abstract: Macroalgae (seaweed) can be cultured effectively for the production of useful algal biomass and removal of nutrients from fishpond effluents. A land-based, tide/gravity-driven flow-through, fish-macroalgae integrated system was studied at Makoba Bay, Zanzibar, Tanzania, during May-October, 2000. Rectangular cages made of 1-inch mesh netting were constructed in channels that received the outflows of the fishponds. Four species of macroalgae were planted in the cages and compared for their usefulness as biofilters. Gracilaria crassa and Ulva reticulata grew at average rates of 1.5 and 1.2 %, respectively. Both species removed nitrogen as seaweed protein at rates of up to 0.4 g N/m2/d. The algal biomass produced was of good quality with protein dry weight contents of 13% for Gracilaria crassa and 26 % for Ulva reticulata. The biofilters also raised the pH values of the fishpond effluents and oxygenated the water. In contrast to Ulva and Gracilaria, species of Eucheuma and Chaetomorpha performed poorly in the fishpond effluents. Description: Research Groups: Department of Plant Sciences, Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel The National Centre for Mariculture, Israel Oceanographic and Limnological Research, P.O. Box 1212, Eilat 88112, Israel

Trophic Ecology of Sardinella gibbosa (Pisces: Clupeidae) and Atherinomorous lacunosus (Pisces: Atherinidae) in Mtwapa Creek and Wasini Channel, Kenya

Tue, 01 Jan 2002 00:00:00 GMT

Title: Trophic Ecology of Sardinella gibbosa (Pisces: Clupeidae) and Atherinomorous lacunosus (Pisces: Atherinidae) in Mtwapa Creek and Wasini Channel, Kenya Authors: Nyunja, J.A.; Mavuti, K.M.; Wakwabi, E. Abstract: The food habits of two schooling planktivorous fishes, Sardinella gibbosa and Atherinomorous lacunosus, were investigated in Mtwapa creek and Wasini Channel of the Kenya coast. Spatial and temporal variations in their food and feeding habits were assessed using the percentage numerical abundance method, percentage frequency of occurrence, stomach fullness indices and the Tokeshi graphical method. This study established a clear spatial separation of Mtwapa creek from Wasini Channel in terms of the abiotic and biotic data. Highly significant differences (t-test, p < 0.05) were observed between the two study areas in temperature, salinity, transparency, conductivity, chlorophyll a and in zooplankton abundance and diversity. The diet of the two fish species showed clear spatial and temporal differences, which were dependent on habitat variability. The two species belong to the omnivorous trophic category. Sardinella gibbosa from both sites fed mostly on copepods during the two seasons. Atherinomorous lacunosus fed mostly on phytoplankton, copepods and nematodes during the NE Monsoon. However, its diet was dominated by nematodes during the SE Monsoon. Overall, both fish species exhibited generalised and opportunistic feeding habits. Their diet was influenced by changes in the quality and quantity of food in the environment and the fishes migratory patterns. Description: Research Groups: Department of Zoology University of Nairobi, P.O. Box 30197, Nairobi, Kenya Kenya Marine and Fisheries Research Institute, P.0. Box 81651, Mombasa, Kenya