Marine Ecology Blog

The importance of jellyfish and how their populations are changing

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 A Box jellyfish (Tamoya spp..) migrates from the deep ocean to feed on zooplankton living at shallower depths.

Jellyfish are pelagic invertebrates that belong to the Cnidaria phylum. Like other members of this group including corals and anemones, jellyfish have the ability to sting using a collection of microscopic harpoons called nematocysts. These organisms have a relatively simple anatomy. They lack any brain, complex nervous system, or digestive system. In fact, 95% of their body is made up of water. Despite their relative simplicity, these organisms that have lived in the Oceans for over 500 million years (outdating dinosaurs by over 200million years) survive extremely well in almost all areas of the world. Jellyfish play an important role in controlling populations of zooplankton through their high feeding rates. In doing so, Jellyfish also create competition for other zooplankton feeders. This helps to prevent any single species from outcompeting all other individuals that feed on a similar diet, which could otherwise significantly reduce biodiversity. Jellyfish are an important food source for other marine organisms including sea turtles, sunfish and spade fish. Furthermore, studies have also suggested that after dying, jellyfish act as an important food source to organisms living in the deep depths of the ocean.

Jellyfish often create important symbiotic relationships with certain species of fish. Tentacles full of nematocysts provide suitable housing and protection to developing larvae and juveniles who are immune to being stung. Fish found living with Jellyfish also benefit from the available food sources that are also associated with the symbiotic relationship. These relationships with developing individuals are significantly important for enhancing the recruitment of certain species of fish to an adult life stage, many of which are of commercial value. One study found that 2/3rd of fish who formed symbiotic relationships with one species of jellyfish were commercially valuable and many of which were still in recovery from previous depletion of stocks. Other observations of symbiotic relationships involving jellyfish have suggested that these animals may act like a cushion to rest on for certain animals when travelling large distances using oceanic currents.

Aside from their ecological importance, Jellyfish have also been used in many areas of research. Their energy efficient movements have regularly been studied, and findings have often been incorporated into mechanical design and engineering.  These animals have also been sent to space to study the importance of gravity on early life development, findings of which may be useful for human space travel in the future. Research looking at the venom of certain jellyfish has also demonstrated its effectiveness in cancer cell inhibition, which may provide useful information in the future development of cancer treatments.

In recent years, Jellyfish outbreaks have been observed to occur more frequently. There are several possible causes of this, however studies have suggested that these outbreaks may be correlated with factors associated with environmental change, overfishing and other anthropogenic effects. Large outbreaks may deplete the available food source available to other competitors including several important invertebrates, corals and fish. This could strongly affect the survival and reproduction rates of these species, leading to a declining trend in their population size. One particular lab study found a significant increase in jellyfish larval production when temperature was increased and suggested similar effects may be seen in response to global warming events. Studies have also suggested that jellyfish outbreaks may be indirectly caused by eutrophication resulting in large populations of plankton. In other areas, such high numbers of Jellyfish have been associated with the lack of competition from commercially valuable fish species due to overfishing and depletion of stock of these competing fish species. Outbreaks caused by any of these are likely to have serious ecological effects on the balance and health of marine ecosystems. 

The Roctopus ecoTrust continuously monitors abiotic (non-living) factors associated with water quality including temperature, salinity and nutrient loads, all of which may influence larval development, adult recruitment, and population size of certain Jellyfish species. Monitoring abiotic factors is important for identifying local areas where water quality may be influenced by anthropogenic (human) activity and is important for understanding the effects these abiotic factors have on marine ecosystems.


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