Most people have expressed relief that there have been fewer jelly-fish sightings this summer, which has in turn encouraged many to take the plunge. But is the absence of jellyfish a reality or just a perception?
Alan Deidun, a marine biologist at the International Ocean Institute -Malta Operational Centre hosted at the University, who is responsible for operating the Spot the Jellyfish monitoring campaign, explains that fewer jellyfish have been seen this year due to the absence of one particular species – the mauve stinger (Pelagia noctiluca).
Dr Deidun said that sightings of this dreaded stinging species constituted about 85 per cent of all jellyfish sighting reports submitted to the Spot the Jellyfish team last year. So any fluctuations in the numbers of this jellyfish did not go unnoticed.
Dr Deidun attributes the success of this species, considered to be a bane of bathers worldwide, to two major factors. Firstly, the species undergoes direct development, which means its reproductive cycle is shorter than that of many other jellyfish species, lasting just one month. Secondly, it reproduces throughout the year, although mostly during the December to January period.
So what caused the virtual disappearance of mauve stingers this summer? Dr Deidun is cautious over the issue, saying various interrelated factors may be responsible.
For example, in published studies abroad, it was demonstrated that the occurrence of mauve stinger blooms or swarms depends mainly on wind speed and direction, surface water currents and on the natural reproductive cycle of the species.
Wind speeds have been higher throughout June and July compared with the same months last year, with the northwest wind (majjistral) being more prevalent.
Some have pointed out to a more sudden drop in sea temperature as the real cause, especially since the mauve stinger can dwell at depths of up to 1,500 metres.
Jellyfish spotters in Spain and Italy are currently recording large mauve stinger aggregations in offshore areas, and this might be indicative of things to come later this summer in our waters, Dr Deidun points out.
The Spot the Jellyfish campaign has contributed to greater public awareness of the diversity of gelatinous species in local waters and of the role these play in marine ecosystems. For example, the campaign recorded a total of 14 gelatinous plantkon species or groups from Maltese waters over the past year, of which eight, marked with an asterisk (*), are new records for Maltese waters.
These include the mauve stinger (Pelagia noctiluca), the by-the-wind sailor (Velella velella), the fried-egg jellyfish (Cotylorhiza tuberculata), the cigar jellyfish (Olindias phosphorica)*, the Portuguese man-o’-war (Physalia physalis), the Mediterranean box jellyfish (Carybdea marsupialis), the crystal jellyfish (Aequorea sp.)*, the moon jellyfish (Aurelia aurita)*, the root-arm medusa (Cladonema radiatum)*, the barrel jellyfish (Rhizostoma pulmo)*, the nomadic jellyfish (Rhopilema nomadica)*, the blue button (Porpita porpita)*, pelagic sea squirts (salps and pyrosomes), and comb jellies (Beroe cucumis, Beroe forskalii and Leucothea multicornis)*.
Dr Deidun prefers using the term ‘gelatinous plankton’ rather than ‘jellyfish’ since the former includes non-stinging species which are also common in Maltese waters. In fact, he points out that at the moment local waters are not completely devoid of gelatinous plankton, as many bathers have reported the presence of salps and comb jellies.
Salps are pelagic sea squirts or tunicates which are much more complex than jellyfish in that they have a rudimentary nervous system and what can be considered as the precursor of the vertebral column in vertebrates.
Salps and comb jellies are both non-stinging species, with the former taking in water through a siphon and filtering out any plankton particles, while comb jellies have sticky, rather than stinging, tentacles.
The latest important discovery made by the Spot the Jellyfish team is that of the dreaded nomadic jellyfish (Rhopilema nomadica) which has plagued the easternmost Mediterranean since its introduction through the Suez Canal in the 1980s.
In fact, this species regularly shuts down electrical power stations as it clogs their cooling water inlet systems, clogs fishing nets and wreaks havoc on the local tourist industry. Dr Deidun points out that the species was only spotted twice in local waters in 2004 and hence there should not be any room for alarm, at least for now.
The Spot the Jellyfish initiative is co-ordinated by Aldo Drago, Dr Deidun and staff of IOI-MOC, and enjoys the support of the Malta Tourism Authority, Nature Trust, Friends of the Earth, Ekoskola, the Blue Flag Malta programme, and, as from this year, Sharklab.
The campaign is an IOI-Kids programme initiative, which follows a citizen science approach and relies on the collaboration of the public, sailors, divers, and especially children and teenagers through their teachers and parents, by recruiting their assistance in recording the presence and location of different jellyfish through the use of a dedicated colourful reporting leaflet.
The leaflet is being widely distributed, and can be directly downloaded from www.ioikids.net/jellyfish, a website that features information and anecdotes about different jellyfish species. Large posters featuring various jellyfish species have also been put up on boards near the islands’ major bays, with the support of the MTA.
The reporting is done by matching the sighted jellyfish with a simple visual identification guide, giving the date and time of the sighting, and indicating the number of jellies seen.
Sightings can also be reported online or submitted through an SMS on 7922 2278, or by sending an e-mail to ioi-moc@um.edu.mt.
Strange jellyfish not included on the leaflet should be caught and kept in a bucketful of seawater before e-mailing the IOI-MOC to try to retrieve and to identify the species. If this is not possible, photos of the jellyfish should be taken.