Invasive Chinese jellyfish colonising British Columbia lakes

An invasive Chinese jellyfish species is colonising the lakes of British Columbia. Scientists from the University of British Columbia note that these thousands of jellyfish are cloning males of the freshwater species Ryder's Hydra.

"Craspedacusta specimens were seen in 34 freshwater reservoirs since August 1990. Most of these reservoirs are generally shallow (less than 10 metres), often natural in origin and have a small surface area (less than 0.1 square kilometres). [...] To date, all the jellyfish examined are males," wrote scientists from the University of British Columbia.

Scientists are not certain, but they suspect that over 30 years ago, the small freshwater jellyfish Ryder's Hydra (Craspedacusta sowerbii) from China accidentally ended up in one of the lakes in British Columbia. It probably got there because aquarium water was dumped or transported by birds.

In the 1990s, the number of jellyfish in British Columbia began to increase rapidly. They are usually observed from July to October. Researchers have noted that since 2012, jellyfish appearances coincide with anomalous weather conditions occurring in July and August.

In an interview with "The Canadian Press," scientists explained that the discussed jellyfish species thrives in warm waters, especially when the temperature exceeds 27 degrees Celsius. The jellyfish are visible only at a temperature of about 25 degrees. One of the researchers noted that before reaching the full jellyfish form, they exist as polyps and develop into jellyfish when the water reaches the appropriate temperature. They maintain the jellyfish form only for a few weeks, until the end of September.

Research has shown that all of the jellyfish found in the lakes of British Columbia are genetically identical, which suggests that male jellyfish have the ability to clone themselves.

Freshwater jellyfish are harmless to humans, and people can swim in the lakes where they are present. However, their impact on foreign ecosystems is unknown.

"It is therefore equally important to understand their ecology in this warming invasive habitat," the researchers emphasised.

In a 2021 article published in the journal "Nature", scientists wrote that the freshwater Asian jellyfish arrived in Europe in the mid-19th century, along with aquatic plants brought to botanical gardens in France and the United Kingdom. This jellyfish has also been found in Australia and Africa. In 1880, Craspedacusta sowerbii was seen outside its natural environment only once, by 1988 already 196 times, and in 2020 as many as 2041 times.