An abnormally high density of 'blue button' jellyfish  around Marsalforn in the past few days. Hundreds of the minute, but unmistakable (in view of their ethereal blue and perfectly spherical bodies), blue button (Porpita porpita) individuals were observed in a small area, clinging on to, and possibly feeding on, tentacles of the mauve stinger (Pelagia noctiluca).

The Spot the Jellyfish team at the University of Malta said the blue button is normally a rare occurrence in Maltese coastal waters and was first recorded from such waters in 2010 by a French girl holidaying in Malta, from Dwejra in Gozo.

The species is normally considered as a tropical one, being known from tropical parts of the Indian, Pacific and Atlantic Oceans, and hence its proliferation in the Mediterranean Sea might be another sign of  warming of the Mediterranean Sea.

The blue button is almost innocuous (since its tentacles might just cause some mild irritation to human skin) and strictly speaking is not a jellyfish as it belongs to the same group as Velella velella (By-the-wind sailor), with floating colonies consisting of several individuals, the team said.

The Spot the Jellyfish initiative is coordinated by Dr. Alan Deidun, Prof. Aldo Drago and staff of IOI-MOC, and enjoys the support of the Malta Tourism Authority (MTA) and of Nature Trust, Friends of the Earth, EkoSkola, the BlueFlag Malta programme and Sharklab.

http://www.science20.com/citizen_science_journal/jellyfish_reporting_citizen_scientists_malta carried an extensive feature on the Maltese initiative.