A COMPARATIVE STUDY OF GROWTH RATES AND YIELD OF THE SEAWEED, Kappaphycus alvarezii (Doty), USING VARIABLE SEEDLING DENSITIES AND CULTURE METHODS IN COASTAL KENYA.

Abstract

Seaweed farming has been demonstrated to have significant socio-economic benefits to coastal communities and has the potential to reduce pressure on wild fishery stocks. This work was aimed at testing sustainable farming technique of the seaweed, Kapapphycus alvarezii, at two sites (Kibuyuni and Gazi) on the south coast of Kenya. Two culture methods (off-bottom and rafts) were tested for growth and yield of the species at five stocking densities (50g. 75g, 100g, 125g, and 150g) replicated three times. The density treatments for Rafts and Off bottom methods were sampled bi-weekly for growth and yield during the northeast (NEM) and southeast monsoon (SEM) seasons during March –July 2014 and November –April 2015. Physico-chemical parameters were measured bi-weekly at each site and related to growth and yield at sites. Data were analyzed using a combination of multivariate and univariate statistics. Results showed mean maximum growth rates (%/day ± SD) of 2.97±0.00 at Gazi at two weeks of culture during NEM season for the rafts, while rates of 2.86±0.10 were obtained at Kibuyuni during SEM season. The Off-bottom method yielded growth rates of 2.73±0.13 after a period of ten weeks of culture during the NEM season in Gazi while the method produced rates of 2.49±0.1 at Kibuyuni at nearly the same interval during the NEM season. At Gazi site,two –way ANOVA showed season and density to have significant effect on growth rate (p<0.05) while, method of culture had no significant effect. The result suggests that Gazi farmers may simply select any of the methods that provide highest growth rate at the shortest time. Season, method and density had significant effect on growth rate at Kibuyuni (p˂ 0.05) indicating all the variables are important to be considered when culturing the species at Kibuyuni. This implies that at Kibuyuni off-bottom method is desirable during SEM and raft method during NEM. The physico-chemical parameters had effects on growth and yield that varied between sites and seasons. These results are discussed in relation to other studies on the same species and recommendations are made based on the data and the constraints of the study.