Jelly of the sea - Nice ones and not so nice

Todays innocent, but unidentified, catch

In Sweden we are only used to see moon jellyfish (Aurelia aurita), but in these waters this wobbly fauna is a bit more diverse. We have stingy ones that destroy the bathing enthusiasm, there are very invasive ones that destroy the eco system, and there are some quite innocent ones. Today both Yoram and Ziv felt that they got a bit stung at some point in the sea, but we never identified the perpetrator. However, we found this other character that has no long tentacles, thus, it cannot sting. I have not been able to put a species name on it yet. It was very beautiful, though, with a clear sky blue colour and quite big. The one in the picture was not the biggest one. We saw one that probably was 20-30 cm in circumference.

Mauve stinger (Pelagia noctiluca)

This is what to watch out for if you want to avoid being stung. This mauve creature has long tentacles which secretes a biological poison that causes severe burning pain on the skin and if large surfaces is stung it can be critical.

Warty comb jelly (Mnemiopsis leidyi)

On the other hand, when you see this bugger, you make the sea a favour by eliminating the devastating invader. It is originally native to Western Atlantic waters, but has spread to other waters.

In the 80s it was introduced to the Black Sea, perhaps deliberate, to deal with a rampant proliferation of phytoplankton. By 1989, the population had reached some 400 specimens per cubic metre, and this caused a dramatic drop in fish populations, by competing for the same food sources and eating the young and the eggs. In 1999 it destroyed the food chain after being introduced in the Caspian Sea.

Since then, it has also spread throughout the Mediterranean basin and the North West Atlantic, most likely carried by ships, and then further into the Baltic Sea. In the latter case its presence and spreading is considered alarming due to the limited circulation caused by the shape of the sea, and the already extremely stressed ecosystem. The Baltic Sea is definitely more sensitive to such a species than Mediterranean waters, but nevertheless, it does not belong in neither and might cause great damage to fish populations.