James Cook University scientists have uncovered more clues towards solving the mystery of where juvenile Irukandji jellyfish live.
JCU researcher Dr Olivia Rowley said even fully grown Irukandji are very difficult to track, as they are only around 35mm long and transparent, while the juvenile polyp stage of the animal is even smaller at just 1 or 2mm in length.
“During stinger season the loss of revenue for the tourism industry is significant and the direct costs associated with treating sting victims in Northern Queensland runs into millions of dollars per year.
“But despite the significant economic consequences Irukandji bring, our knowledge of the distribution and basic ecology of the polyp stage is very limited,” said Dr Rowley.
She said Irukandji polyps had never been found in the wild, and laboratory-bred polyps form the foundation of all research.
The scientists subjected 1240 Irukandji polyps to nine water samples with differing salinities and seven different temperatures while measuring their oxygen consumption and physical condition.
“The idea is that oxygen consumption will change to the extent the polyps like the environment they are in. This means instead of the very difficult job of trying to track them in the open sea we can deduce the specific ocean environments where they are likely to be found,” said Dr Rowley.
She said salinity did not have a significant effect, but oxygen consumption rates increased with water temperature.
“It seems they favour temperatures between about 28 °C and 34 °C. Based on these results, we think the polyps of this species are likely located in an environment with stable temperatures and fluctuating salinities.
“This means we should be looking for polyps in areas different from those in which we find the adult jellyfish – such as estuaries, oceanic margins and potentially the outlets of springs that carry fresh water via submarine channels to the seabed – known as wonky holes,” said Dr Rowley.
She said the findings mean scientists could downgrade the search for the polyps in some areas.
“For instance, adult Irukandji have been found as far south as Fraser Island off the Queensland coast. But winter water temperatures there average around 20 °C, which polyps would find unfavourable,” said Dr Rowley.
She said with this new information in hand researchers can start to piece together potential niche characteristics and gain insight into hypothetical distributions for the difficult to find species.
“With the potential of warming seas to shift the distribution of Irukandji southwards into heavily populated coastal areas this knowledge may become even more important in the future,” said Dr Rowley.
