Module 4 Chapter 31: Migration of jellyfish

Jellyfish are sea-dwelling invertebrates of the cnidarian, or stinging tentacle, phylum. There are several thousand different species, distributed in most of the world’s oceans. They provide interesting examples of ways in which passive and active mechanisms of movement interact. Ocean currents and the wind cause jellyfish to move passively; this movement explains why they sometimes get trapped in large numbers in restricted coastal locations and harbours.

Jellyfish living free in the oceans periodically gather in very large numbers called blooms. Blooms appear to be a form of purposeful collective behaviour driven by reproduction, food abundance, or preferences for particular environmental conditions. When blooms occur in coastal regions, they sometimes lead to mass strandings on beaches, as you can see in Figure 1.

Figure 1 A mass stranding of barrel jellyfish (Rhizostoma spp.) on the Pembrokeshire coast, Wales UK. Source: (12/5/2017). Credit: from BBC News at

In some circumstances, such accumulations of jellyfish may attract turtles and other animals that feed on them.

Figure 2a shows how populations of jellyfish can be tracked using aerial surveys, acoustic trackers, and underwater cameras to give us an idea of their movement patterns. It is also possible to monitor the directional movements of individuals by fitting them with data loggers, as in Figure 2b

Figure 2 (a) The distribution of barrel jellyfish (Rhizostoma octopus) in the Bay of Biscay off Western France, estimated by aerial survey. Coloured dots are proportional in size to the number of jellyfish observed in each location over a five-minute period. (b) A jellyfish medusa fitted with a triaxial acceleration data-logger to monitor diving behaviour, activity, and body orientation. The float compensates for the additional weight of the kit and restores the animal’s neutral buoyancy. Source: Fossette et al., 2015, Curr. Biol. 25, 342–347, February 2, 2015 © 2015 Elsevier Ltd. Published by Elsevier Inc., .Figure 1.

Observations show that jellyfish may move away from the prevailing current and can even move in the opposite direction if the current is not too strong. Such movement is outlined by the different arrows in Figure 3. The distribution of jellyfish can also be strongly influenced by sea temperature and salinity, magnetic fields, gravity, and the low frequency sounds produced by predators.

Figure 3 Examples of swimming movements of barrel jellyfish in the Bay of Biscay compared with the prevailing sea current at different states of the tide. The black arrows show the average movement vector (direction and speed) of the individual animals represented by the radial vectors around the compass circles. The longer blue arrows show the prevailing sea current vector. Source: Fossette et al., 2015, Curr. Biol. 25, 342–347, February 2, 2015 © 2015 Elsevier Ltd. Published by Elsevier Inc., Figure 2.

Some jellyfish make complex behavioural decisions about their movements. Moon jellyfish (Aurelia spp.) off the coast of Washington State and in the Gulf of Mexico gather in circular or ‘hollow’ aggregations. Individuals move up and down in an orbital manner, producing different densities of jellyfish at different depths. This pattern of distribution is not caused by water currents, although the turbulence produced by their collective movement may help to concentrate the plankton on which they feed.

The helmet jellyfish, Periphylla periphylla (Figure 4), feeds on zooplankton in the deep waters of Norwegian fjords, as illustrated in Figure 5. Light penetration is especially poor in this environment and the jellyfish can forage at a range of depths without facing competition from vision-dependent fish. They change their depth over the day according to the amount of light and as the location of the food material changes — an example of an active positional adjustment. Individuals aggregate in these regions by entangling their tentacles, as demonstrated in Figure 6.

Figure 4 A helmet jellyfish, Periphylla periphylla.  Source: Fisheries and Oceans Canada, Moira Galbraith.WoRMS Editorial Board (2022). World Register of Marine Species. Available from at VLIZ. Accessed 2022-02-16. doi:10.14284/170.
Figure 5 Periphylla jellyfish and krill detected acoustically at different times of day in Lurefjorden, Norway. The colour scale indicates the strength of the sonar signal, where red/brown is strongest; the strength of this signal represents the density of biomass present. Source: Kaartvedt, S., Ugland, K., Klevjer, T. et al. Social behaviour in mesopelagic jellyfish. Sci Rep 5, 11310 (2015).
Figure 6 A pair of Periphylla at 109 m depth, photographed 12 sec apart, showing their entangling tentacles. Source: Kaartvedt, S., Ugland, K., Klevjer, T. et al. Social behaviour in mesopelagic jellyfish. Sci Rep 5, 11310 (2015).
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