Jellyfish blowing in the wind and ending up on our beaches
In 2006, biologist Dr John Flux was amazed to find the shoreline at Makara beach (just west of Wellington) littered with vast numbers of little floating jellyfish.
Each jellyfish was roughly the size and shape of slice of lemon, but transparent. They are called ‘‘by-the-wind-sailors’’ because each floats on the sea with a little sail on the upper side of its body. Their Latin name Velella means ‘‘little sail’’.
Being of a scientific mind, Flux tried to count the jellyfish and reckoned there were 10,000 to the square metre of beach, and at least 100 million along the Makara coast. He made further enquiries from the New Zealand Ornithological Society, whose members continually survey birds washed up on our coasts. The bird watchers reported that jellyfish littered the west coast from Northland to Southland. This translates to trillions of by-thewind-sailors.
By-the-wind-sailors are occasionally blown on to coasts all round the world but never in such amazing profusion as round New Zealand so, in 2007, Flux reported on his phenomenal count in the journal of the Marine Biological Association of Great Britain. He counted strandings on Makara Beach again in 2008 and 2012, but this year’s huge strandings were really phenomenal.
Jellyfish have often been headlined round the world in recent years. A huge species clogs fishing nets in Japanese waters, one capsizing a trawler. Others have blocked intake pipes at nuclear power plants and ruined tourist resorts. Newspapers have been quick to demonise jellyfish as ‘‘Deadly Harbingers of the Age of the Jelly’’ or ‘‘Jellyfish Apocalypse’’, but experts are hesitant to say if a global trend exists.
On the one hand jellyfish numbers have risen or fallen spectacularly for 200 years in the Mediterranean Sea, but these days, they are there in big numbers every year. 2015 was a record year for jellyfish in UK waters. On the other hand fewer jellyfish have been counted off the South American coast.
The experts say records of jellyfish numbers are spotty and the eruptions might represent natural cycles of abundance.
Nobody knows why jellyfish appear to be on the increase but there are plenty of theories. Some scientists blame global warming, others blame marine pollution, marine wind turbines and oil-rigs, or more ballast spread from ships.
Others suggest that jellyfish predators, such as fish, have been wiped out in some seas. Jellyfish numbers can build up very quickly as they can clone themselves by simply dividing in two.
A curious thing about by-thewind-sailors is that some of them have left-handed sails, some righthanded. Release a few of them in the open sea and the left-handers will be blown in one direction and the right-handers in another direction. Flux finds that most velellas blown on to New Zealand coasts are right-handers, probably blown here from the southern Tasman Sea. Some strandings were left-handers, others mixed.
It has been known for some time that penguins and petrels eat a lot of jellyfish but Flux was surprised to see gulls feeding on them at Raumati beach last month.