We have been seeing more jellyfish in Malta’s waters lately because the sea’s temperature went down to 14.6 degrees in the first two weeks of March, said Director of the International Ocean Institute - Malta Training Centre Professor Alan Deidun. 

Deidun explained to The Malta Independent how such temperature changes affect the development of jellyfish species – in this case the mauve stinger jellyfish, which is one of the mostly frequently sighted types of jellyfish in Malta.

He said that normally this species, which only lives for a year, reproduces and sheds its eggs between the end of December and the end of March. Then, the eggs take another three months to develop into adults, “so by April to May we then have a big bloom of these young jellyfish.” 

“The development of jellyfish is, like many other things happening in the sea, affected by temperature. So, if normally the development cycle of the mauve stinger jellyfish from egg to adult takes three months, this year it took longer because of the colder than average sea temperatures.” 

Deidun said that this phenomenon ensured that the mauve stinger jellyfish were around for a longer period of time, rather than their usual three months followed a few weeks throughout their bloom. 

“But we had jellyfish developing at different rates, meaning that we had different stages appearing during different weeks and months of the year.” 

He said that this means that people have been seeing jellyfish from January till now. 

Delving into the development stages of this type of jellyfish, Deidun said that normally their “big bloom” happens in April and only lasts for a few weeks “as it cannot last for long because they do not find enough food to sustain themselves.”

Asked whether the mauve stinger will also be seen for a longer period next year, he said that nobody can be certain, as it’s too early for a prediction. 

“What’s happening presumably because of climate change is that there has been a change in seasons. In the summer the sea is remaining warm even into autumn, but then it is taking longer for the sea to cool down as we are seeing warm temperatures even in November and December,” he said. 

He added that this means that the species is reproducing later in the season. 

Asked whether this change is going to affect future jellyfish generations, he said that it will not as their life cycle is very short; however it will affect other living species that feed on it, such as sea turtles and other fish species, since the opportunity to feed on jellyfish will come later than usual. 

Deidun is urging the general public to participate in the ‘Spot the Jellyfish’ campaign which is being supported by the International Ocean Institute and the Physical Oceanography research group. By doing so, teachers parents and children alike will be helping the organisations bring awareness about the local diversity of jellyfish species, through a hands-on exercise involving the reporting of sighting that often swarm close to Malta’s shores and beaches.

One can find more information at their website:  https://oceania.research.um.edu.mt/jellyfish/