FROM Ireland to Spain and as far away as Australia and Hawaii, jellyfish are becoming more numerous and more widespread, showing up in places where they have rarely been seen before.
These see-through marauders are stinging swimmers, forcing beaches to close, clogging fishing nets and blocking the cooling water intake of power stations.
Two Portuguese man o’war were found on a beach in Co Waterford last month and on Friday last, a young girl had to be hospitalised after suffering a severe reaction to a jellyfish sting at Barleycove beach on the Mizen Peninsula.
Irish Water Safety has warned swimmers that there is an increased likelihood of encountering jellyfish around the coast as they are floating on unusual warmer currents that are tracking towards Ireland.
Most people put their increasing presence down to higher than normal summer temperatures this year and last, but that is only half the story, according to marine scientists who fear that the explosion in jellyfish clusters may be signalling an alarming deterioration in the health of the world’s oceans.
They point to a combination of overfishing of natural predators, like tuna and sharks, rising sea temperatures caused in part by global warming and pollution that has depleted oxygen levels in offshore shallows.
“These jellyfish near shore are a message the sea is sending us saying, ‘Look how badly you are treating me’,” marine biologist Dr Josep-María Gili told the New York Times.
“The problem on the beach is a social problem but the big problem is not on the beach. It’s what’s happening in the seas,” said Dr Gili who has been studying jellyfish at the Institute of Marine Sciences of the Spanish National Research Council in Barcelona for more than 20 years.
Within the past year, there have been beach closures because of jellyfish swarms on the Côte d’Azur in France, the Great Barrier Reef of Australia, and at Waikiki in the United States.
Closer to home, several jellyfish ‘hotspots’ have been identified in the Irish Sea where they already have had negative impacts on tourism with beach closures around Dublin as far back as 2005, reflecting the fact that it is not an entirely new phenomenon here.
Dr Gili’s counterpart in Ireland is Dr Tom Doyle of UCC’s Coastal and Marine Research Centre which is based at the Naval Centre in Haulbowline.
He sees jellyfish from a wider perspective, acknowledging their troublesome nature but seeing in them the possibility of economic potential and even tourism.
He is part of a bilateral research project called EcoJel, a collaboration between UCC and Swansea University in Wales that aims to assess the opportunities and detrimental impacts of jellyfish in the Irish Sea.
“There is a concern that the abundance of jellyfish is increasing globally as a result of climate change and degradation of marine ecosystems under the pressure of human activities,” say the research scientists. “In many places in the world, jellyfish blooms have already proved they can have critical socio-economic impacts, eg clogging fishing nets and causing mass mortalities of farmed salmon.”
They are also suspected to prey on certain fish eggs and larvae, limiting the recovery of already weakened fish stocks.
But the EcoJel team also sees opportunities related to jellyfish, suggesting that it may be possible to harvest jellyfish for export to the far-east market where they are a delicacy.
They also see the potential of developing recreational spots for divers to swim with blooms of giant jellyfish, similar to the experience offered by ‘Jellyfish Lake’, a well-known dive site in the Pacific island of Palau.
Wildlife enthusiast Calvin Jones believes a lot more research needs to be done to be certain that this is a permanent phenomenon. “I hear a lot of anecdotal evidence that jellyfish numbers are on the increase around the Irish coast, and that jellyfish blooms are more common than they used to be. But I’m not sure we have the data to back up those assertions yet,” he says.
Jones, a freelance writer, birder and lifelong wildlife enthusiast, is founder and managing editor of IrelandsWildlife.com, a website devoted to expanding our knowledge of nature’s wild creatures.
“Around the world you’ll find examples where researchers have demonstrated unequivocally that jellyfish numbers are on the rise — but pinpointing the exact cause is tricky,” he says. “We simply don’t have enough long-term data to make that kind of analysis.
“If there has been a rise in jellyfish numbers around the Irish coast over recent years then it is likely to be linked to broader changes in the marine ecosystem. Things like the removal of key ocean predators through overfishing, warming coastal waters thanks to climate change, coastal pollution and a host of other factors will all play a part.
“I don’t think we can say with any degree of confidence what’s happening with jellyfish populations around Ireland — but I believe it’s a reasonable assumption that whatever it is, it’s a symptom of our ongoing impact on our delicate coastal environment.”
Jellyfish in fresh water were unheard of — but not any more. In August of last year, a non-native freshwater jellyfish was found in small numbers at three locations in Lough Derg. The tiny jellyfish which are harmless to humans, were first spotted by angler Pat Joyce. Samples were collected by Inland Fisheries Ireland officers who took them for investigation to Dr Doyle and his team in Cork.
He confirmed the identification of the jellyfish as Craspedacusta sowerbyi and also discovered that all individuals were females. This species is native to the Yangtze River system in China, but during the last 130 years it has colonised most continents.
According to Inland Fisheries Ireland, it is probable that the discovery of this jellyfish relates to the wonderfully warm summer that we experienced in Ireland last year, when water temperatures in many watercourses exceeded 25C for prolonged periods. Jellyfish were also reported on Lough Erne.
“This probably stimulated the budding off of the medusae or jellyfish, which pulsed in the warm water in search of plankton prey,” says the IFI.
What concerns them most, though, is how these tiny creatures found their way into Irish lakes.
“The fact that the two watercourses from which the jellyfish was recently recorded are both internationally renowned navigation waterways suggests that boating and perhaps ballast water from newly introduced craft may represent an important causative agent,” says Dr Joe Caffrey, senior research officer with the IFI.
“Boats and cruisers are commonly imported from abroad and are introduced into our waters without having to prove that they were cleaned and disinfected before leaving their country of origin.
“This practice is unacceptable and poses a significant threat to biodiversity in our waters and to their functionality, be it as recreational, amenity or municipal waters. It is imperative that boats being imported into this country carry certificates of disinfection prior to being granted entry if we are to stop the ever-increasing spread of harmful invasive species.”