Jellyfish blooms are likely to be a common sight this summer with rising ocean temperatures one of the main causes of
substantial population growths.
NIWA forecasters have identified a marine heatwave in the waters to the north of the North Island and are keeping a
close eye on sea surface temperatures around the country which have all been above average since October.
NIWA marine biologist Diana Macpherson says jellyfish blooms occur when water temperatures rise, which causes an
increase in the amount of food available for jellyfish to eat.
"Jellyfish numbers increase as a result, then prevailing winds and currents can gather them up into dense groups and
strand them on beaches," she says.
Jellies are important in marine food webs. Their role can be as a predator, prey or as decomposing scraps of food for
suspension feeders in the water, or for bacteria on the seafloor.
Jellyfish blooms can impact industries involved in marine activities such as salmon farms or invade beaches and sting
swimmers. Scientists are discovering that human impacts such as overfishing, pollution and warming oceans are
exacerbating the problem of jellyfish blooms. Unlike most ocean dwellers, jellyfish are set to actually benefit from
these impacts.
While there are about 223 species of Scyphozoa jellyfish worldwide, just 22 are found in New Zealand waters. However,
the term "jellyfish" is used to describe a diverse range of jelly-like creatures including true jellyfish, hydromedusae,
siphonophores, box and stalked jellyfish, comb jellies (Ctenophora) and salps (Chordata).
Diana describes them as one of the most evolutionary primitive group of invertebrates.
"They have no brain, no bones and no heart but they reproduce, eat, and defend themselves or catch prey with astounding
stinging cells called nematocysts, which work a bit like a harpoon that contains venom."
Those stinging cells are what sometimes gives jellyfish a bad reputation but not all are stingers- and comb jellies and
salps don’t sting at all.
"They are all a natural part of the ecology of all oceans. They are resilient and good at what they do."
Her advice in the event of being stung by a jellyfish is to flush the area with seawater to remove the stinging cells,
carefully pluck off any tentacles that might be stuck on, then apply heat to relieve the pain and deactivate the venom.
Using urine to relieve a sting is a popular misconception - there is no way of telling its pH and chemical make-up so it
could actually make the pain worse.
Most stings in New Zealand waters are not serious but jellyfish should be avoided when possible.
Despite their harmful potential, Diana says jellyfish are beautifully mesmerising. One of her favourites is Periphylla
periphylla, the Santa’s hat or helmet jelly. It is a deep-sea species found in all oceans, including in the Ross Sea,
Antarctica. It has a bioluminescent twinkle, a dainty sparkling effect thought to provide camouflage by creating
confusion about its true size and shape, and its red stomach in the dark deep waters looks black and becomes invisible.
The opaque red also helps to hide glow emitted from any recently eaten bioluminescent prey.
Other species likely to be seen at New Zealand beaches include:
- The lion’s mane (Cyanea rosea) - the biggest jellyfish species seen in our waters with a bell that can reach two
metres in diameter and tentacles that can grow up to 36 metres long. It is a pinky brown colour at the top of its bell
and creamy to whitish at its margin, and has four frilly oral arms, eight clusters of tentacles and each cluster has
more than 100 individual tentacles. They occasionally swarm in large numbers and deliver a painful sting.The lion's mane is the biggest jellyfish species in New Zealand waters. Photo: NIWAA lion's mane jellyfish bloom. Stay clear. Photo: NIWA
- The moon jellyfish (Aurelia) - this one has a discus-shaped, ghostly whitish-transparent bell with a scalloped margin
that bears hundreds of short, fine tentacles.. They are capable of only limited motion, primarily drifting with the
current. They are usually up to 25 cm in diameter, potentially up to 40 cm or greater. It can be recognised by its four
pinkish-purple crescent-shaped gonads easily seen through the top of the bell. They have little or no sting. This
species can occasionally bloom in large swarms, which poses potential problem for salmon farms as they can cause mass
fish kills by suffocation from the jellies’ mucus and irritation from their stinging cells.
- Spotted jellyfish (Desmonema gaudichaudi) - known for dark polka dots on their bodies and 30cm long tentacles. Like
the lion’s mane it has four long curtains of oral arms, and its long tentacles are arranged into eight clumps that hang
from inside the bell (rather than the margin) in a straight line, and delivers a painful sting.The spotted jellyfish delivers a painful sting. Photo: NIWAThe common blue bottle is still capable of producing stings even after stranding itself on land. Photo: NIWA
A NIWA e-guide to jellyfish can be found here: https://niwa.co.nz/coasts-and-oceans/marine-identification-guides-and-fact-sheets/Jiggling-Jellyfish