Update on the jellyfish swarming dynamics along the southern coast of Kerala

Surya, S and Jasmine, S and Saravanan, Raju and Kingsly, H Jose and Albert Idu, K A and Suresh, K K and Dispin, D and Santhosh, B (2025) Update on the jellyfish swarming dynamics along the southern coast of Kerala. Journal of the Marine Biological Association of India, 67 (2). pp. 70-76. ISSN 2321-7898

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Abstract

A comprehensive survey on jellyfish diversity and distribution, conducted along the coastline from 2017 to 2021, documented 12 scyphozoan species, in addition to one species each from Cubozoa and Hydrozoa. Collections were mostly from the fishing gears, beach seine and ring seine. Frequent jellyfish species observed included Acromitus flagellatus, Crambionella spp., Chrysaora spp., Netrosoma sp., and Cyanea spp., with Cephea, Thysanostoma, and Rhopilema being rarely encountered. The study highlighted notable seasonal swarming patterns, particularly with Crambionella sp. in the post-monsoon months (October and November), showed an average count of 200-800individuals per net, while swarms of Chrysaora spp. could reach into the thousands per haul. The swarming season typically begins withNetrosoma sp. (blue jelly) in July-August, followed by Chrysaora spp. and Crambionella sp., continuing until December-January. Environmental factors like the depletion of predator species due to overfishing, climate warming, and the construction of marine structures are likely contributing to the increased jellyfish population. These blooms play a significant role in the coastal ecosystem, where some jellyfish species act as filter feeders and others as predators, impacting local food webs. For fishers, large jellyfish blooms are a challenge, often leading to heavy loads during beach seine operations. Addressing the environmental drivers behind jellyfish blooms through a comprehensive management approach could help mitigate their impact on both ecosystems and fisheries.

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