Growth rates of Eucheuma denticulatum and Kappaphycus alvarezii (Rhodophyta; Gigartinales) cultured using modified off-bottom and floating raft techniques on the Kenyan coast

Abstract

The study compared relative growth rates (RGR) of Eucheuma denticulatum and Kappaphycus alvarezii under modi- fied off-bottom (MB) and floating raft (FR) culture techniques on the southern coast of Kenya. Seasonal variability in RGRs was evident over 10 months in both techniques and sites. RGRs were in the range of 0.9 – 10.2 % d ̄1 for E. denticulatim and 0.3 – 5.7 % d ̄1 for K. alvarezii at Mkwiro, and -0.2 – 7.3 % d ̄1 for E. denticulatum and -1.7 – 4 % d ̄1 for K. alvarezii at Kibuyuni. The RGR of 4.3 ± 0.4 % d ̄1 from the FR technique was significantly higher than the 3.2 ± 0.4 % d ̄ 1 from the MB technique (P ˂ 0.05). Strong oceanic waves which were accompanied by the loss of seaweed thalli in the MB technique at Mkwiro between April and June led to significantly higher RGR in the FR than in the MB (P ˂ 0.05). The higher percentage herbivory, epiphytes, and susceptibility to ‘ice-ice’ (white and soft thallus) associated with K. alvarezii than E. denticulatum in both techniques led to the former having significantly lower RGRs than the latter. Further research on the stability of MB in deep water and accessibility of FR techniques is recommended prior to commercial adoption.