Population distribution and impact of Crown-of thorns starfish, Acanthaster planci (L), on some coral reefs of Zanzibar
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Date
2009
Authors
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Publisher
University of Dar es Salaam
Abstract
Distribution patterns age-size structure and population density of Crown-of –thoms starfish The starfish, Acanthaster planet (L), were determined on Murogo on the western side and Mnemba on eastern side of Zanzibar Island. Feeding rates of young, sub-adult and adult starfishes, preferred prey (coral) species and sizes, and densities of the starfish within and between two reefs were compared. showed clumped and regular distribution at Murogo and Mnemba reefs, respectively. Sub adults (20-30 cm) starfishes dominated the populations in both reefs. With 6 1% for Murogo and 54% for Mnemba. The habitat mean densities (individuals/hectare) at Murogo were 3125 ± 12 13, 248 ± 140 and 2280 ± 1163 for lagoon, 116 ± 114, 44 ± 35 and 67 ± 31 for slope, 220 ± 162, 30 ± 20 and 60 ± 55 for crest, and 13 ± 5, 40 ± 22 and 87 ± 96 for flat during first, second and third sampling, respectively. For Mnemba, mean densities were 28 ± 30, 22 ± 31 and 27 ± 23) for first, second and third sampling, respectively. Densities at Murogo showed significant differences among and within habitats . The differences were in reef flat and lagoon for among habitats and in lagoon and reef slope for within habitat s. Between sites, results showed that Mnemba densities were significantly lower from that of Murogo habitats. Mean feeding rates (cm2/day) were 114, 232 and 244 for young, sub adults and adults, respectiveI). The means were not statistically different due to high variances Pontes and Ethiopora of middle (30-60 cm) and large (> 60 cm) size were preferred at Murogo while small (<30 cm) and large (>60 cm0 size were preferred at Mnemba roof. There was positive correlation between the size of the starfish and size of the coral colonies preyed. This study indicated that the density of the starfish at Murogo is above threshold level and poses threat to coral reefs porites is the most vulnerable coral genera during starfish feeding Moreover, the study point out that type of growth form of coral colony determine preferences.
Description
Available in print form, East Africana Collection, Dr.Wilbert Chagula Library, class mark (THS EAF QL377.C5Z36U76)
Keywords
Seleractinia, Coral reefs, Unguja Island, Zanzibar, Tanzania
Citation
Ussi, A.M