New light has been shed on the population dynamics and genetics of the Mediterranean box jellyfish (Carybdea marsupialis) in various local yacht marinas by a dissertation study by Kristian Pulis, a Master’s student at the University’s Department of Physiology and Biochemistry.

The study’s main aim was to investigate whether the blooming of this species, which in Malta is almost exclusively restricted to yacht marinas, was associated with specific environmental factors. It also sought to conduct a comparative genetic study of different Mediterranean box jellyfish populations.

Pulis monitored the abundance of adult individuals of the jellyfish species in question on a fortnightly basis from July 2014 to July 2015 at St George’s Bay in Birżebbuga, Msida, Ta’ Xbiex and Marsascala, which are popular mooring locations.

Photo: Kristian Pulis

The jellyfish were collected during 30-minute periods using a hand-held net and artificial light.

The results indicate that the abundance of the box jellyfish population was strongly and positively correlated with sea temperature but negatively correlated with phytoplankton density and chlorophyll a.

During the study Pulis also maintained a small colony of Carybdea marsupialis polyps after collecting spawning females from local yacht marinas.

Genetic analyses results indicate a high degree of homogeneity between the genetic sequences of all the analysed Mediterranean box jellyfish populations, while the genetic material from the eastern Atlantic (Cadiz) individuals clearly separated from that of the Mediterranean populations.

The dissertation was supervised by Marion Zammit-Mangion and Alan Deidun and partially funded under the Master It scholarship scheme supported by the European Social Fund.