Ulva reticulata and Gracilaria crassa: Macroalgae That Can Biofilter Effluent from Tidal Fishponds in Tanzania
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Western Indian Ocean Marine Science Association
Abstract
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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 G. crassa and 26 % for U. 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.
Keywords
macroalgal biofilters, seaweed, yield, protein content, integrated mariculture, nutrients, eutrophication, sustainable development