Previously unknown in the Maltese islands, sea bottom-loving ‘upside-down’ jellyfish Cassiopea andromeda showed up in a Sliema harbour four years ago.

The first jellyfish to enter the Mediterranean from the Indian Ocean via Suez Canal was possibly not even noticed at the time. It was 1869 when the canal joining the two bodies of water was completed and opened to sea traffic.

Today, native species in the Mediterranean are facing no fewer than 682 invading alien species, some brought in from other marine environments by ballast water from shipping. Others make their way slowly but surely northwards and westwards from Suez, as far as Spain and beyond.

These alien invaders are entering the Mediterranean at a steady rate of over a dozen new species per year – higher than anywhere else in the world. In 1903, a species of jellyfish previously unrecorded in the Mediterranean was seen in waters off Cyprus. Normally residing in shallow waters, the same species, Cassiopea andromeda, was spotted in Marsamxett harbour four years ago.

Countries with their shores on the eastern Mediterranean have been feeling the impact of these alien invasive species ever since.

Power and desalination plants are severely challenged when jellyfish blooms threaten to overwhelm them

Power and desalination plants on this coastline are severely challenged when jellyfish blooms threaten to overwhelm them. In 2011, the Hadera power plant on the Israeli coast was forced to shut down when a gelatinous mass of these stingers clogged its cooling water intake.

Outbreaks or ‘blooms’ of this tropical invader – the nomadic jellyfish Rhopilena nomadica – can have both economic and environmental consequences. Photo: Shaun Arrigo

Seven desalination plants producing half of Israel’s drinking water are also at risk. In the event of a ‘jellyfish attack’, engineers would need to increase energy-intensive backwash cycles, resulting in a higher discharge of chemicals into the marine environment.

At an international conference on the impact of jellyfish blooms held in Malta last month, specialist Bella Galil, from Israel’s National Institute of Oceanography, described how the threat was spreading to coastlines extending around the Mediterranean Sea after hitting the Levant.

Huge swarms lasting up to six weeks in summer are causing hospitalisations for stings with lingering adverse effects. It’s not good for tourism and disrupts fishing, clogging nets and making it difficult to sort yields.

Invasive alien species of jellyfish affect populations of native species, leaving them strikingly and irreversibly changed, and there is no going back. Up to 30 per cent of alien species substantially affect ecosystem functions. It is impossible to eliminate them… the only thing we can do is adapt.

The temperature of the Mediterranean is possibly still low enough to discourage some thermophilic species that prefer warmer waters, but this has been changing in the past decade.

Voracious feeders, competing with plankton-eating fish for the same food source, jellyfish can be opportunistic feeders, including tuna small fry among their prey. Even the seemingly innocuous ‘blue sailor’ velella vellella has an insatiable appetite for fish larvae.

In warm waters the jellyfish can digest faster, which means they devour even greater quantities. A swarm can be as long as 180km by two kilometres wide and 40 metres deep.

Even when quite far offshore they still can still pose a hazard to humans. Fine filaments from the ghostly white Rhopilena nomadica can break off and be swept towards the shore, giving bathers the sensation of ‘swimming in a sea of nettles’.

In 2011, an invasion of Australian jellyfish forced closure of six beaches in Spain after over a hundred swimmers were treated for stings.

Conference host and senior lecturer at the International Ocean Institute – Malta Operational Centre, Alan Deidun spoke on the Spot the Jellyfish campaign, which started off as an educational activity for children supported by Malta Tourism Authority.

Forecasting and mapping of jellyfish blooms are important tools for beach management. This month a reporting system will be set up on beaches whereby anyone can send data and photos to the Med-JellyRisk website. The national contact point for the project, which also involves partners from Italy, Spain and Tunisia, is the University’s Department of Biology.

In warm dry years there are more arrivals, and the summer ahead is predicted to provide ideal conditions for these invaders in the Mediterranean. Even when the jellyfish seem to have disappeared during the colder months, they may simply have descended to their winter quarters deep in sea canyons.

A coastal survey of jellyfish in marine conservation zones at Bizerte, Sousse and Monastir was presented by Prof. Nejib Daly, a specialist in zooplankton and ecology from Tunisia.

According to a University of Malta survey involving local fish farmers, jellyfish blooms have so far posed no significant impacts to the aquaculture business although most operators believe the invaders are on the increase. At least five different species have been spotted in large numbers around fish farms in Maltese waters.

The mauve stinger has been known to have a negative impact on farmed fish health in other countries as it can irritate the gills and even transmit fish pathogens. A large bloom can clog cooling water intake on inboard motor boats used by the industry.

Bogue (vopi), a small fish which used to be more abundant around local shores, is a valuable predator of the infamous mauve stinger, being partial to the gonads of this particular jellyfish.

A dissertation on the socio-economic impact of jellyfish blooms on Maltese beaches was presented by Gwyneth Tanti.

The fried egg jellyfish (a mild stinger) is under scrutiny by Italy’s Inter-University Consortium of Marine Sciences, which is interested in its anti-cancer properties. In general, jellyfish are a largely unexplored pharmacological research area. The perception of jellyfish outbreaks in local seas may change as more is learned about them.

Supporting local authorities to prevent damage by jellyfish includes training for lifeguards and a first aid handout for jellyfish stings as part of the Med-Jelly Risk project. Treatment of stings varies widely depending on the type of jellyfish, although in all cases a basic rinsing with sea water and removal of tentacles with a plastic card is advisable.

Anti-jellyfish nets as a tool to keep bathing zones safe were demonstrated at St George’s Bay on the second day of the conference. These floating barriers against jellyfish made by Ribola, an Italian net-making family of four generations, have the potential to reduce public health costs from treatment of jellyfish stings. The nets must be removed when sea conditions are expected to reach Force 4.

A smartphone app offers the public a jellyfish risk meter for each beach and a handy indication on how to treat a sting for different species.

www.jellyrisk.eu