The Viability of Red Alga (Gracilaria salicornia) Seaweed Farming for Commercial Extraction of Agar at Kibuyuni, South Coast Kenya

Abstract

Seaweeds refer to several species of macroscopic multicellular marine algae that can be classified into red, brown and green types. Seaweeds are farmed for their products that are used in food, pharmaceutical and cosmetic industries. Commercial farming of Eucheuma denticulatum and Kappaphycus alvarezii seaweed species for production of carrageenan polysaccharide which has wide applications were initiated at Kibuyuni south coast, Kenya in 2010 and 2014 respectively. However, farming of K. alvarezii, which is valued for its high quality carrageenan content collapsed, possibly owing to adverse environmental conditions, thus undermining the potential economic gains by the community. This study was carried out in Kibuyuni from January to December 2017, using the 'off-bottom' seaweed farming method, to investigate the growth of Gracilaria salicornia seaweed species for commercial production of agar, in order to bridge the gap created by the collapse of K. alvarezii farming. The growth rate, seed yield and agar yield of G. salicornia were determined and compared between three sampling sites (A, B & C) and between North East Monsoon (NEM) and South East Monsoon (SEM) seasons. The mean annual growth rate of G. salicornia was significantly different between experimental plots (p < 0.05). The overall mean annual growth rate of G. salicornia at Kibuyuni farm area was 1.471 ± 0.307 (% day-1 ± SD). Significant differences were not found in annual seed yield between the experimental plots (p > 0.05). The overall mean annual seed yield of G. salicornia at Kibuyuni farm area was 3.51.± 0.135 (kg rope-1± SD). Significant differences in mean daily growth rate between NEM and SEM seasons were found in plot B after 14 days culture period (p < 0.05) but not in the rest of the respective plots and culture periods ( p > 0.05). The overall growth rates of G. salicornia at Kibuyuni farm area during NEM and SEM seasons were 1.387 ± 0.9213 and 1.585 ± 0.991 (% day-1± SD) respectively, but were not significantly different (p > 0.05). Mean seed yield did not differ significantly between NEM and SEM seasons in respective plots and culture periods (p > 0.05). The overall seed yields of G. salicornia at Kibuyuni farm area during SEM (3.640 ± 0.6790) and NEM (3.425 ± 0.587) (kg rope -1 ± SD) were significantly different (p < 0.05). The mean annual agar yield (% dry weight ± S.D) after 42 days culture period were not significantly different between the plots (p > 0.05). The overall mean annual agar yield of G. salicornia harvested at Kibuyuni farm area was 51.51 ± 6.02 (% dry weight). The mean agar yield obtained during NEM season (51.21 ± 6.14) was not significantly different from agar yield of SEM (52.47 ± 5.54) season in the three plots (P > 0.05). These findings compare favorably with others from previous studies and thus suggest that commercial farming of G. salicornia at Kibuyuni farming area is possible. However, there is need to conduct further studies.