KARACHI: As the world marked the World Jellyfish Day on Nov 3, experts called for carrying out studies on the causes and dynamics of jellyfish blooms that have become a serious global concern in recent years.

Generally, they said, the occurrence of jellyfish blooms was attributed to climate change. But other factors such as overfishing, eutrophication (due to organic pollution), alien invasions and habitat modification, they believed, could be important factors contributing to their formation.

“The reasons for the sudden increase in the population of some jellyfish and formation of large blooms are not fully understood and there is a need for comprehensive research on their dynamics and their role in coastal and offshore ecosystems,” said Muhammad Moazzam Khan, technical advisor (Marine Fisheries) at the World Wide Fund for Nature-Pakistan (WWF-P).

Last month, he pointed out, large dead jellyfish species were found scattered over the beaches in Gwadar and Clifton.

“They feed on plankton, crustaceans, small fish and fish eggs. Therefore, they deplete the food resources of fish and even larger mammals like whales,” he said.

Major threat to fisheries

According to the information available with the WWF-P, a major bloom of jellyfish Crambionella orsini was observed in the Arabian Sea, including Yemen, Oman, Iran and Pakistan in May 2002 and August 2003 and again in December 2019 which continued till August 2020.

Large numbers of Crambionella orsini have resulted in the reduction of catch of commercial fishing operations along the Pakistan coast.

It also caused massive clogging of nets and interrupted the operation of seawater cooling systems of power plants and ships. As the bloom was ubiquitous, fishing operations such as tuna gillnetting were practically stopped in offshore waters, affecting the livelihood of thousands of fishermen.

Similarly, shrimp and fish trawling in the coastal and offshore waters were impacted, resulting in choking of trawl nets within a short span of time.

The WWF-Pakistan previously reported a major mushroom jellyfish (Rhopilema hispidium) bloom from the offshore waters from Karachi to Ghora Bari, along the Sindh coast.

In Ormara, along the Balochistan coast, another bloom was observed which was caused by stinging jellyfish (Pelagia noctiluca) that clogged fishing nets. In addition, handling or removal of this jellyfish from fishing nets can inflict severe and painful stings.

Jellyfish exports

While jellyfish blooms have several negative impacts, jellyfish harvesting and processing have been an important economic activity along the coastal areas of Sindh and Balochistan till recently.

“The activity is now seeing a decline due to over-harvesting. Still, exports of jellyfish to China continue, where it is considered a delicacy. It’s treated with salt and alum and exported in semi-dried form from the Indus Delta, Miani Hor, Kalmat Khor and other bays along the Balochistan coast,” said Khan.

According to him, there are more than 50 processing units that have been set up in these areas along the Sindh and Balochistan coast.

It is estimated that about 2,500 tonnes of processed jellyfish is annually exported to China. Last year, however, these exports were affected due to the economic slowdown caused by Covid-19.

Published in Dawn, November 4th, 2021