Back in September, I posted an article about the summer invasion of sea jellies in Monterey Bay, CA. I was there to conduct an underwater video workshop for the BLUE Ocean Film Festival and found me and my students surrounded by thousands of sea nettles.
I learned that these mass gatherings of sea jellies of various species were becoming more frequent worldwide. However, scientists were unsure as to the reasons why. There were certainly some likely possibilities including pollution, loss of predators, and climate change, but as far as most scientists were concerned, it was all inconclusive. There's much we don't know about these beautiful invertebrates, so making definitive statements is difficult at best.
But the invasions continue. The BBC News reports of a rise in sea jelly, or jellyfish, swarms in the United Kingdom. And scientists there are beginning to subscribe to the same suspicions I referenced in my previous post.
"It's not only beach-goers who have to watch out. Torness nuclear power plant in Scotland recently had to shut down after moon jellyfish blocked the water intake system. Several tonnes of the creatures had to be cleared out.
Some areas, including the Irish Sea and the east coast of Scotland, have been invaded by so many they now resemble a 'jellyfish soup', says the Marine Conservation Society (MCS). So why do they appear to be on the increase?
According to research there is strong evidence that an increase is linked to three main factors - pollution, overfishing and possibly climate change.
Overfishing means jellyfish do not face their usual predators and competitors, which usually regulate population growth. Large fish, which eat jellyfish, have been drastically reduced by bad fishing practices, says Ocean 2012, a pressure group which campaigns to stop overfishing. So have smaller fish which compete for food with the stingers.
It is argued that climate change can cause more favourable conditions for jellyfish, with their adaptability giving them an advantage over some other sea creatures."
Sea jelly swarms - also known as blooms, like plankton blooms - apparently have occurred in the cold North Atlantic waters from Ireland to Scotland to England. A few research organizations have been conducting tagging studies and surveys to learn more about their distribution, but the sparse data comes in slowly so, once again, conclusions are hard to come by.
Says Dr. Victoria Hobson of Ecojel, a 3-year old research project on the abundance and distribution of sea jellies, "This [the lack of research] also makes it difficult to get a handle on how numbers have changed. Even in recent years people are doing a lot more watersports so are spotting more. With the development of smartphones it is also much easier to report those sightings. It makes it difficult to interpret if there are actually more jellyfish or just more sightings."
Sea jelly invasions can have serious economic consequences. In Nambia, swarms of sea jellies have consumed or pushed out many local fish species, depriving subsistence-level fisherman of any catch whether for sale or for their own consumption. And in developing nations hard hit by either civil strife or severe drought conditions (or both), a loss of a local food source can have grave implications.
In more developed nations, like Japan or Great Britain, sea jelly swarms can spoil entire commercial catches. In 2007, a jellyfish invasion wiped out Northern Ireland's only salmon farm, killing over 100,000 fish.
Beautiful to look at, fascinating to watch, and sometimes dangerous to the touch, sea jellies can be seen as an indicator as to the health of the oceans and whenever they appear en masse, we should all take notice. It could mean a lot more than just the need to be careful where you step on the beach or in the surf.
Read about UK's sea jelly invasion in the BBC News.
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