There currently exists no direct data on the effect of water quality or global warming on Irukandji populations, either in the sense of numerical increases or geographical spread.

However, many independent data sets on other species of jellyfish from around the world, along with incidental laboratory observations, do suggest some interesting trends.

WATER QUALITY: All jellyfish appear to have the capacity to exploit perturbed ecosystems, effectively taking over the role of top predator and efficiently excluding other species from re-establishing. Factors such as turbidity, hydrocarbons, eutrophication, and decreased biodiversity, seem to have little detrimental effect, instead opening up niches vacated by other species with narrower ranges of tolerance. Once established, most jellyfish are able to bloom in massive numbers, exerting a double-whammy on the ecosystem: they prey directly on small larvae, as well as on the plankton food sources that the larvae would eat. Thus, other species find it increasingly difficult to regain a foot-hold.

WATER TEMPERATURE: Box jelly and Irukandji jellyfishes are generally reported at water temperatures above 26°C. In laboratory conditions, 1-2° warming results in stressed animals that do not recover; animals generally deteriorate rapidly and expire if not maintained in cool water. Cooler water retains more dissolved oxygen, allowing animals to absorb it with less energy expenditure; cubozoans, with a higher metabolism than most other jellyfishes, and thus higher oxygen demand, probably have a narrow range of tolerance and low adaptational potential. Although the jellyfish are able to swim well, and thus navigate in and out of variable local conditions, the populations are nonetheless tied to regions where their polyps can survive; cubozoan species and populations typically have extremely narrow distributions, suggesting that they are unlikely to adapt easily to alternative habitats if conditions were to become intolerable.

Summary of published conclusions: Most authors have concluded that the jellyfish situation is likely to worsen in coming years, as human activities continue to impact on marine environments and other species are affected, opening up niches for jellyfish.

BOTTOM LINE: It seems likely that non-thermal perturbations are likely to result in increased jellyfish numbers, whereas thermal perturbations are likely to have detrimental effects on box jellyfish and Irukandji populations, but enhancing effects on some other species. Targeted local data are urgently needed to be able to make confident local predictions.

For more information, see:

Arai, M.N. (2001) Pelagic coelenterates and eutrophication: A review. Hydrobiologia, 69-87.

Graham, W.M., Martin, D.L., Felder, D.L., Asper, V.L. & Perry, H.M. (2003) Ecological and economic implications of a tropical jellyfish invader in the Gulf of Mexico. Biological Invasions, 5, 53-69.

Lynam, C.P., Hay, S.J. & Brierley, A.S. (2005) Jellyfish abundance and climatic variation: contrasting responses in oceanographically distinct regions of the North Sea, and possible implications for fisheries. Journal of the Marine Biological Association of the United Kingdom, 85, 435-450.

Mills, C.E. (1995) Medusae, siphonophores, and ctenophores as planktivorous predators in changing global ecosystems. ICES Journal of Marine Science, 52, 575-581.

Mills, C.E. (2001) Jellyfish blooms: Are populations increasing globally in response to changing ocean conditions? Hydrobiologia, 55-68.

Parsons, T.R. & Lalli, C.M. (2002) Jellyfish population explosions. La Mer, 40, 111-121.

Purcell, J.E. (2005) Climate effects on formation of jellyfish and ctenophore blooms: a review. Journal of the Marine Biological Association of the United Kingdom, 85, 461-476.

Zaitsev, Y. & Mamaev, V. (1997) Marine biological diversity in the Black Sea: a study of change and decline. United Nations Publications, New York, 208 pp.