Jellyfish, Vavu'a, Kingdom of Tonga
Wednesday, September 15, 2010 at 7:14PM 
“jellyfish, Jellyfish” I yelled as the boat powered through the calm water of the harbour to the jetty. The Tongan crew reduced power to the twin Yamaha engines bringing the boat to a crawl and gave me questioning glances – why was this Australian yelling about jellyfish after diving with Humpback Whales and calves….. Many people find jellyfish spineless, uninteresting, blubbery blobs of marine gelatine at the whim of the ocean currents and prevailing wind – not so!
Jellyfish evolved during the Precambrian Explosion roughly 545 million years ago. Since this time, jellyfish (or Medusa) have evolved into many distinct species. Many species are very similar if not identical to those in the Cambrian Period. As such, these species have the distinguished name “living fossils”.
Whilst it’s true that jellyfish are at the mercy of the wind and currents, many species have the ability for locomotion. Swimming (the jellystroke) is accomplished by muscular contraction of the dome-shaped umbrella, or bell, which forces water out of the cavity and propels the medusa in the opposite direction. When the muscles relax (after contraction) the bell expands again as water enters the cavity. Rather than swim horizontally, many jellyfish move vertically within the water column to take advantage of surface winds and or sunlight. Some species migrate to great depths during the evening to rise again to the water’s surface at first light.
LEFT: I photographed this jelly looking towards the surface of the water from a depth of roughly 7 meters using a 16-35mm f2.8 lens @ 16mm f14.
All jellyfish have stinging cells called nematocysts. The nematocysts are usually located within the arms or tentacles of the jellyfish and are used to immobilize prey that floats by. The arms then either deliver the prey to a cupola (bell) or digest the meal from the actual tentacle. Although some jellyfish have tentacles that trail from the cupola for up to several meters, most are not dangerous to humans and lack nematocysts “harpoons” powerful enough to penetrate human skin. A few species, however, are exceptionally dangerous to swimmers and divers and include the Portuguese Man of War (Physalia physalis) and Box Jellyfish (Chironex fleckeri).
As I slipped into the harbour water I immediately noticed that although the water visibility was quite good, the hue of the water was a light green. As clouds obscured the sun the water become dark and gloomy. I could see several jellies and I snorkelled amongst them looking each over in turn attempting to find a decent specimen to photograph. At one stage the jellies seemed to consolidate themselves and I couldn’t see much further than the next jellyfish; thankfully I was wearing a thin lycra skin which I knew provided ample protection if I brushed against any nematocysts. I was seeking a jelly that was not at the water’s surface as I wanted to place the sun directly behind the jelly to obtain a starburst effect. Finally, I discovered what I thought was a good-looking jellyfish, and diving down to a depth of 7 meters I positioned my housing beneath the jellyfish’s cupola shooting towards the surface. Interestingly, it appeared that every time I positioned myself close the jellyfish it manoeuvred away from me, sometimes descending and at other times ascending. I had initially thought a “jelly shot” would be easy but after 15 minutes snorkelling and repeatedly diving to 7 odd meters I was beginning to think otherwise! The Tongan boat crew were getting anxious – not so much for the elapsed time but more to do with sharks. They continually reminded me that these waters were home to tiger sharks and I must admit some trepidation when I began to think of what exactly was around and below me in the this green gloom.
LEFT: Jellyfish with light rays. To capture the light rays I ensured that the sun was part was in the frame and the f stop was greater than f14 (16-35mm f2.8 @f14), no strobe light.
So next time you see some jellies in the sea, think how old they, overcome your anxiety of getting stung, jump into the water and check them out – you’ll be surprised at how graceful and beautiful they are and will never again refer them to them as “spineless jelly blubbers”.
Reader Comments (3)
Hi Iain - where are you? No coffee lately. Love the pictures of the spineless jellyfish. I've often seen these but have never thought of getting into the water with them - next time I will though
Fantastic shots! really love your choice to include the lightrays streaming through, and interesting how challenging it was for you to get them to cooperate for this shot.
Thanks Pat - I've always enjoyed swimming with jellies.