Yield determinants of Kappaphycus alvarezii seaweed in South Sulawesi, Indonesia

Abstract There has been limited systematic monitoring of seaweed growth with simultaneous measurement of important yield determinants. This study reports on Kappaphycus alvarezii (Cottonii) seaweed experiments in South Sulawesi, Indonesia. The first (June – Oct 2023) experiment showed lower yields for the lowest seedling weight and similar yields for the medium/high seedling weight. During this period, seaweed losses from lines (empty ties), ice-ice disease and fouling by epiphytes increased. The second experiment (March – July 2024) showed high yields for the traditional longline and low yields with tube-nets and cages, due to fouling by epiphytes and mud. Yields did not differ systematically between villages and did not differ systematically between nearshore and further offshore. Yields were highest for planting in March and lowest for planting in August. Stronger winds and rougher sea towards October were shown to be an important yield determinant, but not the only one. During the March-October period losses from lines increased, pressure from the ice-ice disease increased, fouling by mud and epiphytes increased, temperatures decreased and windspeed increased. Yields in the March-October cultivation cycles were determined by a combination of the effects of these five yield determinants. To our best knowledge the current study is the first to study this full range of possible yield determinants and to simultaneously monitor for longer period (five cycles, with bi-weekly sampling) both seaweed biomass and yield determinants.