A lot of the beaches have warned of Jelly fish in the sea and advise not to swim. Though it has been said this is not connected to the earthquakes at El hierro.

I have spotted a few red ones in the Papagayo waters just recently, so they are present but I don't think in large numbers. Where did you find the warning ?

The town beach at in Playa Blanca has signs also there is a warning sign at Dorada beach not to swim. i read a report in the voz that it is not related to the eruptions at El Hierro, but due to water currents.

According to a post on another forum Playa Chica & Playa Grande in PDC were closed on 7th Nov due to high numbers of jellyfish

The turtles will be along next to eat the jellyfish. Then the sharks will be along to eat the turtles. Surfers and especially boogieboarders should be aware.