Experts term climate change a possible cause of frequent jellyfish blooms

Posted on 03 November 2021

Karachi, November 3, 2021:  Due to frequent jellyfish blooms, it is not unusual to see dead jellyfish casted on the beaches in large numbers. In the last week of October 2021, the beach at Gwadar (West Bay) was littered with dead mushroom jellyfish (Rhopilema hispidium), whereas in early October 2021, high water at Clifton was covered with dead hydromedusae (Aequorea pensilis). Scientists all around the world are bewildered because of the frequent occurrence of jellyfish blooms. Generally, the appearance of the blooms is attributed to climate change but other factors such are overfishing, eutrophication (due to organic pollution), alien invasions and habitat modification are all possible and important contributory factors.
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. 
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. 
Increased frequency of the occurrence of jellyfish blooms is a serious global concern being highlighted and stressed upon on World Jellyfish Day, which is celebrated globally on 3 November. As these blooms have a number of negative impacts, jellyfish are being exported to China, where they are considered a delicacy. This helps mitigate their large numbers. Jellyfish is 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. There are more than 50 processing units that have been set up in these areas, and jellyfish harvesting and processing are established as important economic activities along the Sindh and Balochistan coasts. It is estimated that about 2,500 metric tons of processed jellyfish is annually exported to China, however, now there is a decrease in the quantity of jellyfish being exported to China due to unreliable landings and economic slowdown because of Covid-19.
According to Muhammad Moazzam Khan, Technical Advisor (Marine Fisheries), WWF-Pakistan, the jellyfish blooms are a function of natural cycles or the result of human impacts on the environment. According to him, the reasons for the sudden increase in the population of some jellyfish and forming of large blooms are not fully understood. Jellyfish blooms, according to him, feed on plankton, crustaceans, small fish and fish eggs, therefore, they deplete the food resources of fish and even larger mammals like whales. He emphasized the need to conduct comprehensive research studies on the causes of these bloom formations. ‘While celebrating this Jellyfish Day, we must stress on the need to undertake further research on jelly bloom dynamics and their role in coastal and offshore ecosystems’, he added. 
Hamera Aisha, Manager (Marine Programme), WWF-Pakistan pointed out that WWF-Pakistan intends to study the socio-economic impact of jellyfish fisheries in the Indus Delta as it is becoming an important economic activity in the area. She emphasized the need for creating awareness about these invertebrates, which are generally ignored by fishermen as well as by scientists.
Jellyfish specimen from Arabian Sea
© WWF-Pakistan