Effect of seagrass cover and mineral content on Kappaphycus and Eucheuma productivity in Zanzibar
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The productivity of two species of red algae, namely Eucheuma denticulatum (Burman) Collins et Harvey and Kappaphycus alvarezii (Doty) Doty was investigated at Paje and Uroa, two sites in Zanzibar differing in seagrass cover. The growth rate (GR) of E. denticulatum in Paje (low seagrass cover) was 20–75% lower than in Uroa (high seagrass cover), depending on season. Growth of K. alvarezii in Paje was compromised by Polysiphonia spp. epiphytism. Manganese, iron, copper and zinc contents of both E. denticulatum and K. alvarezii from Paje were 35–99% lower than in E. denticulatum from Uroa. Culturing of epiphyte-infested or healthy K. alvarezii in seawater fortified with the mentioned minerals improved daily GR by 10–200 %. The effect of Cu, Zn and Mn in K. alvarezii with epiphytic infestation and ‘ice-ice’ was positive only when Provasoli solution was added. The GR of E. denticulatum was virtually unchanged by the addition of minerals. It is suggested that Fe, Zn, and especially Mn may p.....