Seaweed farming shifting from shallow intertidal water to deep subtidal waters: enhancing productivity, sustainability and resilience in blue economy

Seaweed farming is one of the fast growing mariculture sector with a growth of about 9% globally. This growth is supported by the increasing need for marine algal food, industrial and biofuel uses among others. In Kenya, seaweed biomass production hardly reach the tonnage required to satisfy the market demand. Massive loss of seaweeds in the farms during the dry season that lead to inadequate seaweed seeds to supply to farmers during the conducive season has been associated with this challenge. Growth performances of seaweeds cultivated in deep water environment using the HDPE constructed floating raft and those cultivated in shallow environment using the off-bottom technique were monitored at Mkwiro in Kwale County for five months from January to December 2026. Results showed that the specific growth rate was significantly higher (2.65% day-1) for seaweeds grown using the floating raft than those grown using the shallow water off-bottom technique with 1.22% d-1. The higher growth performance of seaweeds in the floating raft was triggered by presence of lower percentage seed loss, epiphytic load and ice-ice attack as compared to the higher percentages of the same parameters observed in the shallow water technique. Further results showed that the HDPE-constructed floating raft is suitable for growing seaweeds in deep water. However, the tension strength and stability of the floating raft and selection of suitable materials for its construction should be properly considered to attain optimum results.