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Causes of the Increase in Jellyfish Blooms

Paper Type: Free Essay Subject: Environmental Studies
Wordcount: 2530 words Published: 8th Feb 2020

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Jellyfish are members of the phylum Cnidaria, like all members of this phylum they’re radially symmetrical. The radial symmetry allows jellyfish to detect and respond to food or danger from any direction. (NOAA, 2018).

Jellyfish are simple creatures, composed of 95% water, while the remaining 5% consists of the necessities required to exist as successful marine organisms. (Lamb, 2017). They’re Composed of three layers; the outer layer is knowns as the epidermis, the middle layer involves the mesoglea, a jelly-like substance, the inner layer is called the gastrodermis. Jellyfish have a straightforward nervous system that gives them the ability to smell, detect light, and respond to different stimuli. Jellyfish have a gastrovascular cavity (digestive cavity) that acts as both the intestine and the stomach, with one opening for the mouth and anus. (NOAA, 2018). Jellyfish have two structural types, these are the two main stages of a jellyfish’s lifecycle, known as the polyp and the medusa.

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 Jellyfish can be distinguished by their possession of cnidocytes, the main type being nematocysts. These are located on the tentacles and resemble are like harpoons which eject venom, allowing them to capture and hold onto prey drifting through the water column. (Lumen, n.d.). Jellyfish do not have complete control over their movement, they use a muscle to propel themselves forwards, by expanding and retracting their bell. This is the main reason why they float in currents and appear in large swarms known as a “bloom”. (NOAA, n.d.) 


Around the world, masses of jellyfish swarm together to form blooms, causing a multitude of problems. Recent studies show that the effects jelly blooms have on economical, ecological and social impacts are drastically increasing and intensifying.


Unlike other marine animals, the lack of complexity in jelly fish allows them to be extremely adaptable to changes in environmental conditions. These changes may be naturally occurring or human induced.(Kienberger et al., 2018)

Factors that often restrict other marine organisms may include hypoxic (low oxygen) zones, acidic water, increase in ocean temperature, pollution, and light sensitivity, don’t affect jellyfish in the same way. (Alberts, 2014)



Juli Berwald, marine scientist, has stated that Jellyfish reproduce much quicker in warmer waters. These polluted areas are suitable because they require less oxygen that other sea life. (ABC News, 2019) https://www.abc.net.au/news/2019-01-06/the-magic-and-mayhem-of-jellyfish/10377112


Global overfishing is a major factor contributing to the losses of the highest marine predators and other ecologically important species. According to Philippe Curry from the Research Institute for Development in France, overfishing is a primary cause in the uprise of jellyfish blooms. Turtles and Tuna are two of the jellyfish’s main predators and their populations are depleting due to overfishing (WWF, n.d.). Due to these circumstances, jellyfish are thriving on taking advantage of small pelagic fish.

Both Cnidarians, and these small fish such as Sardines, herring, and anchovies, feed on Zooplankton. This means they are the jellyfish’s main competition for food. In locations where these fish populations are depleting, ecological niche is cleared up, allowing jellyfish the opportunity to increase their populations. However, these small fish feed on the larvae of jellyfish and when their populations are higher, the number of jellyfish larvae and juveniles may be outweighed. Under typical conditions this cycle may be regulated (Systems, 2013), however the fluctuations of this cycle is intensifying, adding additional strains to the resilience of low fish populations affected by overfishing. (Boero, 2013)


Researches have demonstrated the impact of overfishing by investigating and comparing two locations joined by the same ocean current, the Benguela of South Africa. Location one is placed off the coast of Namibia. This site is poorly managed, there are no enforced restrictions on their fishing activities and Their fish stocks are unable to regenerate fast enough.  From this the team found that jellyfish blooms are increasing and overtaking these coastal waters. Location two is 1000km further south of South African coasts. This site is monitored closely, and their policies for fishing have been well enforced for over 60 years, with no drastic increases in jellyfish blooms. (Roux et al., 2013)


Eutrophication has been highlighted as a driver for the growing abundance of jellyfish. (Boero, 2013)

eutrophication occurs when there is a high abundance of plant and algal growth, this may be influenced by multiple factors needed for photosynthesis. (Schindler, 2006). These may include, carbon dioxide, sunlight and nutrient fertilisers. Eutrophication is a naturally occurring process that has been occurring for centuries as water bodies age and fill with sediments (Carpenter, 1981). However, the effects of eutrophication in coastal waterways have risen due to human interactions involving the land, by discharges of limiting nutrients known as Nitrogen and phosphorus into marine ecosystems. (chrislock et al., 2018)

Jellyfish thrive in water conditions of low dissolved oxygen. Many marine species are unable to cope with these conditions and their populations begin to plummet or are forced to move into new niches.

The ongoing effects of eutrophication also plays a toll on the larger marine animals such as turtles, larger fish, and other marine mammals as there is a shortage of food. With the predator prey relationship no longer enforced, this allows jellyfish populations to rapidly expand. (Pirl et al., n.d.)

The limitations of food sources are not a problem for these gelatinous creatures, due to their diet being so diverse. Because jellyfish are not active eaters, almost anything the come across can serve a source of nourishment.  Because jellyfish can reproduce so rapidly, they’re able to survive these harsh conditions. Polyps can be sessile on the bottom of an ecosystem for long periods of time, until conations are favourable enough to release and become swimming medusas. Furthermore, increases in jellyfish blooms causes less diversity and energy production in marine ecosystems. (Pirl et al., n.d.)


A recent study conducted by a team at the Ecological Society of America (2013) has examined the hypothesis that artificial structures associated with aquaculture, shipping, and other coastal industries acts as a habitat for jellyfish polyps, thus providing them with more shelter and allowing their populations to expand.


It was the early 1980’s when jellyfish blooms became were identified as an issue, particularly in the Mediterranean Sea. During this time, the United Nations Environment programme (UNEP) created a program that would consider these blooms a sort of biological pollution. This encourages research

There are numerous research techniques taken to monitor these blooms;

  1. Diving

Divers observe and count jellyfish over a fixed period of time. Divers must remain at a given depth

  1. Boating

Jellyfish are identified and counted from a boat. 

  1. Birds eye view

Jellyfish are monitored from small air crafts, to cover larger areas over shorter periods of time

  1. On shore view

Jellyfish are washed ashore, and observed as stranded walking along beaches

  1. Submersibles

This method reveals the large abundance and diversity of jellyfish is deeper waters. Although this method is very expensive, it encourages the opportunity for new research and more photographic reactors and collections of specimens.

Positive and negative

Although jellyfish are becoming an inevitable nuisance to human activity, these gelatinous creatures still hold an important role in the ecological society and should remain a well-respected creature.


Are they good or bad?

-          Jellyfish are very important and should remain a respected creature. 

-          They are a source of food to large fish and turtles.

-          Provide habitat to many juvenile fishes

-          They can protect these small fish from being eaten by predators (what is this relationship called) with their stinging cells

-          Many young crabs will ride on top of the jellyfish’s bell so they don’t need to swim

-          They can be extremely useful in terms of human medicine practices

Locally what can we do?


During periods where blooms are at their peak, they can become clogged in fishing nets. Their combined weight can destroy fishing gear. In one case reported in Japan, a vessel sank due to the weight of gelatinous plankton they were pulling up in the net. It is not only the impairment of gear that is the issue, but the process taken to remove jellyfish from the nets is incredibly tedious.   file:///C:/Users/Lily/Downloads/GFCMStudiesReviewNo92_Boero_Finalforweb%20(1).pdf


Tourism is a large source of income for coastal locations around the world. The increase of jelly blooms are causing damaging ecological consequences.  Queensland where tens of thousands of people seek treatment after being stung at these popular beaches. Due to this, some of Australia’s beaches have had to close threatening Queensland’s $12bn tourism industry. 


  • ABC News. (2019). https://www.abc.net.au/news/2019-01-06/the-magic-and-mayhem-of-jellyfish/10377112. Retrieved from https://www.abc.net.au/news/2019-01-06/the-magic-and-mayhem-of-jellyfish/10377112
  • ALBERTS, C. (2014). Jellyfish Swarms are Bad News for Ocean Ecosystems. Earth Island Journal. Retrieved from http://www.earthisland.org/journal/index.php/articles/entry/jellyfish_swarms_are_bad_news_for_ocean_ecosystems/
  • Boero, F. (2013). Review of jellyfish blooms in the Mediterranean and Black Sea. GENERAL FISHERIES COMMISSION FOR THE MEDITERRANEAN92. Retrieved from https://www.researchgate.net/publication/285034759_Review_of_jellyfish_blooms_in_the_Mediterranean_and_Black_Sea
  • Carpenter, S. (1981). Submersed Vegetation: An Internal Factor in Lake Ecosystem Succession. The American Naturalist118(3), 372-383. doi: 10.1086/283829
  • Chislock, M., Doster, E., Zitomer, R., & Wilson, A. (2019). Eutrophication: Causes, Consequences, and Controls in Aquatic Ecosystems | Learn Science at Scitable. Retrieved from https://www.nature.com/scitable/knowledge/library/eutrophication-causes-consequences-and-controls-in-aquatic-102364466
  • Kienberger, K., Riera-Buch, M., Schönemann, A., Bartsch, V., Halbauer, R., & Prieto, L. (2018). First description of the life cycle of the jellyfish Rhizostoma luteum (Scyphozoa: Rhizostomeae). PLOS ONE13(8), e0202093. doi: 10.1371/journal.pone.0202093
  • Lamb, J. (2017). The Global Jellyfish Crisis in Perspective. Jstor Daily. Retrieved from https://daily.jstor.org/global-jellyfish-crisis-perspective/
  • Lumen. Phylum Cnidaria | Boundless Biology. Retrieved from https://courses.lumenlearning.com/boundless-biology/chapter/phylum-cnidaria/
  • Natty and Polly Wallpaper. (2019). JELLYFISH BLOOM – NAVY [Image]. Retrieved from https://www.nattyandpolly.com.au/jellyfish-bloom-navy/
  • NOAA. (2018). What are jellyfish made of?. Retrieved from https://oceanservice.noaa.gov/facts/jellyfish.html
  • NOAA. What Are Jellyfish?. Retrieved from https://floridakeys.noaa.gov/animals/whatrjellies.html
  • Pirl, W., Pirl, E., & Fagan, J. The Effects of Eutrophication on Jellyfish Populations in New Jersey Waterways [Ebook]. Retrieved from https://rucore.libraries.rutgers.edu/rutgers-lib/39567/PDF/1
  • Roux, J., van der Lingen, C., Gibbons, M., Moroff, N., Shannon, L., Smith, A., & Cury, P. (2013). Jellyfication of Marine Ecosystems as a Likely Consequence of Overfishing Small Pelagic Fishes: Lessons from the Benguela. Bulletin Of Marine Science89(1), 249-284. doi: 10.5343/bms.2011.1145
  • Schindler, D. (2006). Recent advances in the understanding and management of eutrophication. Limnology And Oceanography51(1part2), 356-363. doi: 10.4319/lo.2006.51.1_part_2.0356
  • Systems, e. (2013). 426 – Boom in jellyfish: overfishing called into question – Institut de recherche pour le développement (IRD). Retrieved from https://en.ird.fr/the-media-centre/scientific-newssheets/426-boom-in-jellyfish-overfishing-called-into-question#intertitre1
  • WWF. Overfishing. Retrieved from https://www.worldwildlife.org/threats/overfishing


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