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Masters level study sheds light on box jellyfish populations within our yacht marinas

05 February 2016

A Masters level dissertation just completed by Mr. Kristian Pulis within the Department of Physiology and Biochemistry within the Faculty of Medicine and Surgery, under the supervision of Dr. Marion Zammit-Mangion and Prof. Alan Deidun, has shed new light on the population dynamics and genetics of the Mediterranean box jellyfish (Carybdea marsupialis) sampled within a number of local yacht marinas. The main aims of the study involved the investigation of whether a number of environmental parameters were associated with the blooming events of the Cubozoan species in question, which, within Maltese coastal waters, is almost exclusively restricted to yacht marina areas, and a comparative genetic study of local box jellyfish populations and populations within Tunisian waters and along the Mediterranean (e.g. Denia) and Atlantic (e.g. Cadiz) coasts of Spain. Carybdea marsupialis s.l. is a Cubozoan which is native to the Mediterranean and other contiguous seas, which delivers a painful sting and whose numbers within coastal areas allegedly increased greatly in recent years.

In order to achieve the first aim, the abundance of Carybdea marsupialis adult individuals was monitored on a fortnightly basis over the July 2014-July 2015 period at four locations known to support a high density of recreational vessels: Birzebbuga (St. George’s Bay), Msida, Ta’ Xbiex and Marsascala. Such collection was done through the use of hand-held net collections of individuals under artificial light over a period of 30 minutes. At two of these locations (Msida and Birzebbuga), a number of morphological parameters were also measured on ten box jellyfish individuals during each sampling event. For the same period of interest, satellite values for a number of water quality descriptors were also accessed, including nutrients, chlorophyll a, dissolved oxygen, pH, salinity, surface temperature and phytoplankton density, and any possible correlations between these biotic and abiotic factors and phenological characteristics of the sampled box jellyfish populations were investigated. Results indicate that, interestingly enough, box jellyfish population abundance at the Maltese sampled sites was strongly and positively correlated with sea temperature and negatively correlated with chlorophyll a and phytoplankton density. The student also managed to maintain a small colony of Carybdea marsupialis polyps after collecting spawning females from local yacht marinas during the study.

The genetic characterisation of the different Carybdea marsupialis samples was carried out through the analysis of the mitochondrial 16S rDNA region and the region between the 18S and 28S of the rDNA. Results indicate a high degree of homogeneity between the genetic sequences of all the analysed Mediterranean box jellyfish populations, whilst the genetic material from the eastern Atlantic individuals separated out clearly from that coming from the Mediterranean populations. This result further confirms the taxonomic conundrum which surrounds Carybdea marsupialis, which might very well represent a species complex, although further studies are necessary to support such a hypothesis. The genetic analyses embarked upon within this study will in fact be amplified within the coming weeks and the outcome will eventually be published in a scientific paper.

This study was partially funded under the MasterIt! Scholarship scheme within the framework of the European Social Fund (ESF).