Does a seasonal decrease in water temperature influence the condition of the upside-down jellyfish?
Species of Cassiopea (commonly known as ’upside-down jellyfish’) can negatively impact fisheries, tourism and the surrounding ecological environment through predation, competition, and reducing water quality by lowering oxygen content and releasing stinging cells. Distribution and abundance of upside-down jellyfish appears to be closely correlated with temperature.
Cassiopea are invasive on a global scale and while previously distributions in Australia were contained to the tropics, since 2013 there have been reports further south along the East coast of Australia. They were first reported in a restricted area of Lake Macquarie, NSW in 2017, and since then have been discovered in an additional nine sites around the lake.
The abundance of Cassiopea within Lake Macquarie seems to be seasonal as they have only been recorded from mid-summer until late winter. Of the environmental parameters currently being monitored (including salinity, turbidity, temperature, dissolved oxygen, and pH), temperature seems to the most closely correlated to their abundance patterns. Hypotheses for why the jellyfish disappear after the onset of colder water temperatures include migration or cell disintegration leading to death.
To test the relationship between water temperature and cell disintegration in Cassiopea we simulated the natural decrease in Lake Macquarie’s seasonal water temperature within the Ian Potter Aquarium at SIMS to assess the physiological response of the jellyfish. Additionally, the experiment was replicated at predicted climate change temperatures in order to determine if Cassiopea blooms will become aseasonal.
Data from the study is yet to be fully analysed but observations suggest a decline in water temperature, at rates recorded in the field at Lake Macquarie, does lead to the onset of cell disintegration leading to death in Cassiopea. This has significant implications regarding the influence Cassiopea may have on the Lake Macquarie ecosystem and their ability to spread to other locations.