Use of Jellyfish as a potential organic fertilizer and its effect on the growth of okra, <em>Abelmoschus esculentus</em>

Abstract

Jellyfish are free-floating gelatinous animals belonging to the subphylum Medusozoa of the phylum Cnidaria. Nineteen jellyfish species have been reported in Sri Lanka and their abundance is found to be high (making 15,600 tons biomass per year). The seasonal occurrence of jellyfish blooms is widespread along the coast of Sri Lanka, interfering with human activities, including tourism and fisheries. This study aims to assess the possibility of using jellyfish blooms as a commercially available organic fertilizer. Highly abundant four jellyfish species, Lychnorhiza malayensis, Chrysaora sp., Chiropsoides buitendijki, and Marivagia stellata in the coastal waters of Sri Lanka were selected for this study. Using the traditional composting procedure, jellyfish fertilizers were prepared and the total nitrogen, phosphorus, potassium, water holding capacity, and pH of each fertilizer were assessed using standard procedures. The effectiveness of these fertilizers was tested by treating them separately on Okra (Abelmoschus esculentus) plants (n = 10 per treatment) once a week with a positive (commercial-grade compost) and negative control. Height, number of leaves, flowers, and fruits of each plant were recorded weekly for 10 weeks. All jellyfish fertilizers had higher phosphorus (10.01-22.09 g/kg), and lower potassium (0.66-1.88 g/kg) levels than the commercialgrade compost (~10 g/kg; ~5 g/kg, respectively), and their nitrogen levels ranged from 6.24 to 23.34 g/kg. The fertilizers prepared using L. malayensis (15.12 g/kg) and Chrysaora sp. (23.34 g/kg) showed significantly higher nitrogen content than that of commercial-grade compost (10 g/kg; p < 0.05; ANOVA). The average height and growth rate of plants treated with jellyfish fertilizers and commercial-grade compost were mostly within the same range during the experimental period of 10 weeks. Plants treated with jellyfish fertilizers showed flowering between 35 to 40 days, where compost-treated plants showed no evidence of flowering within the experimental period. Further studies are warranted on the potential use of jellyfish as a potential organic fertilizer that can be widely promoted locally.