Swarms of jellyfish along east coast

Large numbers of jellyfish were spotted in several bays by timesofmalta.com readers yesterday, an occurrence that seems to be recurring with greater frequency with each passing year.

The blooms of Pelagia noctiluca, or purple stinger jellyfish as they are commonly known, were seen along Malta's eastern coast all the way from Ta' Xbiex to Birżebbuġa.

Marine biologist Patrick Schembri said: "There are many things that contribute to increased numbers of jellyfish appearing. Usually, it means environmental factors would have been good for reproduction."

Prof. Schembri added that their appearance in such large numbers could not be put down to one factor but several, such as a lack of predatory species, plentiful food supply (they feed on plankton and other small organisms) and favourable currents that wash them inshore.

Jellyfish do not really pose a problem at this time of year, because barely anyone goes swimming during the winter months. They have been troublesome in previous summers, however, causing people to stay dry for fear of being stung.

A scientific report published yesterday by University of Malta researchers indicated that another jellyfish species, Cassiopea andromeda, had been spotted in Maltese waters.

The species, commonly known as the upside-down jellyfish, is a circumtropical species found in warmer parts of the Atlantic and Pacific oceans, including the Red Sea.

It is not a native of the Mediterranean but it entered through the Suez Canal and established populations in the Levantine Sea and Aegean Sea, where it is now quite common.

Until now, no populations of Cassiopea andromeda were known further west than the southeastern Aegean Sea. A team of researchers - Prof. Schembri, Alan Deidun, and Patrick Vella - came across an aggregation of at least 50 specimens close to the mouth of Marsamxett Harbour last March.

The jellyfish, ranging in size from an umbrella diameter of three to 11 centimetres, were carpeting the muddy sand bottom at a depth of 3.5-6m. Remnants of this aggregation were still present at the end of June.

Although they sting, these particular jellyfish are not dangerous because their sting is very mild and most people do not feel it at all. It is not known how they arrived in Malta. The research team believe the most likely explanation is shipping, either in ballast water or on the hulls of vessels.