Jellyfish blooms sighted in estuaries in coastal north Kerala have become an increasing cause of concern for fishermen, as it makes it difficult to catch other types of fish.

Representational image of a jellyfishImage for representation
news Environment Thursday, February 11, 2021 - 18:03

By Amrita Mohan, Mongabay

In the early hours of the day, when the sky is clear and blue, swarms of jellyfish wade through the waters surrounding Kavvayi islands, some four kilometres from the nearest town, Payyanur, in Kannur district of Kerala. “It is a beautiful sight indeed. When you watch them slowly propel themselves through the water, they don’t even seem that dangerous,” says Satheeshan T.V. a fisher worker from the island. Aesthetics aside, jellyfish blooms sighted in estuaries in and around Kavvayi as well as Madakkal, Nileshwaram, Padanna, Valiyaparamba and neighbouring regions in Kasargod district have become a cause for concern for the fisher workers here.

Sighted from November to March, jellyfish blooms are almost an annual phenomenon in these coastal regions of North Malabar. However, their scale has increased at an unprecedented rate, observe fisher workers from the region. “Normally, we wouldn’t mind. We have been sighting them every year, so you expect them to bloom at this time. We try to avoid trapping them in our nets as much as we can. But now, it appears that their numbers are increasing at a steady rate, so much so that some of us have to stop going for work for days,” says Madhu, a long-time fisherman, who stays near Madakkal.

Jellyfish is a collective term for any umbrella-shaped gelatinous animal in marine waters and is considered the oldest multi-organ animal found on earth, having overcome 500 million years through natural selection. Over 90 percent of a jellyfish’s body is composed of water. Experts estimate that India is home to around 50 jellyfish species, out of which at least 20 species have been identified in Kerala. Around six species of these have reported regular blooms in the state. A 2016 article by A. Biju Kumar and Riyas A., published by Society for Environmental Education Kerala (SEEK), has elucidated that jellyfish blooms have been notably increasing in Kollam district’s Paravur, Elathur and Korappuzha in Kozhikode, as well as Nileshwaram and Padanna in Kasargod.

While venomous stinger jellyfish species have been reported across the globe, regional scientists say that most of the species found in Kerala’s coasts are not fatal and can, at the most, induce itching and swelling, upon contact.

Jellyfish woes for fisher workers, aquaculture

The discomfort caused by certain jellyfish is such that the indigenous species has been named after it. The local name for jellyfish is ‘kadal chori’, which literally translates to  ‘sea-itch’. In Kavvayi and neighbouring regions in Kannur and Kasargod, they are also called ‘kanjaampothu’. However, the fisherfolk also mention that not all jellyfish are harmful. “There is a white jellyfish (Acromitus flagellatus) with black patches on its umbrella, which is mostly innocuous and commonly seen here, especially near the mangroves. There is another yellow jellyfish (Chrysaora caliparea), and it’s more dangerous. If you touch it, it stings for a second and then you start itching. There’s nothing you can do but wait for it to pass,” says Sandeep CK, who works as a tourist guide and fisher worker in Kavvayi.

Yellow-coloured jellyfish (Chrysaora caliparea) that causes severe itching, found in Kavvayi backwaters. Photo by Amritha Mohan.

Apart from the severe itching, fishers are troubled by jellyfish that clog their nets; it is often an arduous task to shake them off. With the ongoing prawns and shrimps season, the presence of jellyfish makes it difficult to efficiently catch other types of fish, say the workers. “During the prawns season, we throw our nets hoping for a good catch, but what do we get instead? Hundreds of jellyfish. If their liquid splashes on our face or eyes by accident while we shake them off our nets, our eyes begin to swell. We’ll have to stay away from work if that happens,’ says Satheeshan.

These free-swimming animals are known to reduce the marine resources available for catch, and reduce the number of fishing days for fishermen. For instance, a study published by the Central Marine Fisheries Research Institute (CMFRI) in 2015 found that jellyfish are also known to feast on sardine larva in substantial quantities. This has the potential to disrupt the marine food chain as well, the study suggests. T. Purushothaman, a shrimp farmer from Payyanur and president of Aquaculture Development Cooperative Society (ADCOS), further observes that these jellyfish were found preying on post-larva shrimps, which affects their breeding. “During the time of high tide, we’ve seen jellyfishes swim along with post larva shrimps, and feed on them. This ultimately has an impact on the recruitment of shrimps,” said the aqua-farmer, who is also the recipient of the Jagjivan Ram Innovative Farmer award instituted by the Indian Council of Agricultural Research (ICAR).

Coastal aquaculture is one of the fastest-growing industries in India, with a total of 1.53 lakh (153,000) hectare area in nine maritime states under shrimp culture producing 6.8 lakh (680,000) metric tonnes of product, data sourced from Marine Products Export Development Authority (MPEDA) shows. Such “rapidly increasing aquaculture/mariculture/cage culture practices can act as a catalyst for jellyfish swarming,” a study on jellyfish aggregations, published in 2020, found.

Other industries such as tourism, power generation, desalination, and shipping have also reported considerable economic losses due to jellyfish blooms. “Jellyfish are known to sting swimmers and tourists in Kerala’s beaches. Sometimes, dead jellyfish collectively deposit on the shores of the beach, which impacts the aesthetics of the region,” observes Savitha Mohanan K.M., a research scholar from Kannur University, who has also worked as a project assistant in the Fisheries Department in Kanhangad.

Jellyfish (Lychnorhiza malayensis) stranded on a beach in Thiruvananthapuram. Photo by A. Biju Kumar.

Causes for jellyfish surge

While there is no scientific consensus on whether jellyfish are exponentially increasing at a quantifiable rate across the globe, it is safe to argue that the jellyfish blooms have been increasing, rather than decreasing, in most places where they have been studied. A 2012 study (by Brotz et al.) showed a 62 percent increase in jellyfish blooms out of the 45 Large Marine Ecosystems (LME) studied across the world, wherein the Arabian Sea also noted an increasing trend. Jellyfish blooms have been sighted in Thiruvananthapuram, beaches in Goa, Mumbai, Visakhapatnam, Odisha among other coastal regions.  In India’s west coast, “majority of blooms occur towards the end of the southwest monsoon (June-September); blooms of Crambionella orsini start towards the end of monsoon and last still post-monsoon (October-January), while Acromitus flagellatus blooms occur in backwaters during November-May,” a study by Riyas A. and Biju Kumar, Department of Aquatic Biology and Fisheries under University of Kerala, note

What are the possible reasons for this increase in the number of jellyfish blooms along the coast of Kerala? As per regional scientists and marine biologists, this surge is attributed to several factors, both natural and man-made ones. A variety of natural factors, including winds, changing tidal movements, surface currents, water temperature, salinity, dissolved oxygen, as well as man-made factors- such as water quality deterioration, eutrophication, overfishing, translocation, habitat modification have a significant role to play here.

“The complex life cycle of this Cnidarian species is a major contributing factor for its unique existence, which is often impervious to rising temperatures and lack of oxygen in the water. They can survive in such conditions, as opposed to other marine beings. Therefore, a rise in sea temperature and global warming can facilitate these blooms,” says Riyas A., research scholar.

Jellyfish are often found trapped between the roots of mangroves, which are home to a variety of fishes. Photo by Amritha Mohan.

But researchers also mention that it would be wrong to say that climate change is the only reason for this global phenomenon. “Kerala’s coastal infrastructure can be another factor. Two-thirds of the state’s seawalls are made of granite, providing a hard surface for jellyfish larva to settle and multiple,” notes A. Biju Kumar. Increasing marine activities, which lead to rising nutrient levels in the sea (particularly phosphates, leading to eutrophication) can increase the productivity of planktons, which jellyfish mostly feed on. “When the number of planktons increases, jellyfish also increase. Its natural predators like sea turtles and swordfish are supposed to prey on jellyfish and maintain the balance of the marine food chain, but when there are fewer predators, it is only natural that jellyfish populations surge,” added the professor.

The way forward

Scientists are united in their opinion that not only are there no quick-fixes to this issue, but also that such an approach would be detrimental to the study of the species. “We are yet to efficiently and economically utilise the jellyfish found in Kerala’s coasts, as opposed to states like Andhra Pradesh, which started engaging in jellyfish processing, trade and export to Southeast-Asian countries four to five years ago,” observes Dinesh Kaippilly, Head of the Department, Aquaculture, Kerala University of Fisheries and Ocean Studies ( KUFOS). Export earnings from jelly fish in the state are negligible: In the last 20 years, exports have remained at a meagre 1,092 tonnes in the state.

It was only in 2000, when large numbers of jellyfish blocked the cooling system of the Madras Atomic Power Station (MAPS) in Kalpakkam, Tamil Nadu, that discussions on jellyfish blooms and their consequences gained spotlight in India. “Lack of adequate background and historical data pertinent to the region is a major deterrent for jellyfish studies. This is because the species had no economic value earlier, and it is only now that some research is being done on its export and trade value. Its impact on aquaculture also needs to be scientifically studied, because this definitely has ramifications on the marine economy of the state,” says Biju Kumar. The species’ taxonomic diversity and complex life cycle make it further challenging for researchers to properly categorise and mark their surge in population because the rate of jellyfish blooms are often variable and irregular. It is in this hope that the University of Kerala plans to host the Seventh International Jellyfish Bloom Symposium at Thiruvananthapuram in 2022, in an attempt to address the gap in the region’s jellyfish studies.

Scientists, therefore, call for a holistic understanding of the surge of jellyfish blooms. While this seems to be linked to human activities, their mechanisms need to be thoroughly researched, due to the significant impact it has on marine ecosystems and human beings. Fisher workers, meanwhile, are on the look-out for other options, like new devices, to tackle the jellyfish influx.

This article first appeared on Mongabay and can be found here

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