Cannibalistic Jellies

 

Every time you go there you encounter a whole new set of animals and there always seems to be one that predominates".

 

That was a comment I made to the crew before we departed from the UK on an Imax filming expedition to the Great Barrier Reef in November 1993. We were bound for the Northern end of the Reef - a continental Island aptly named Lizard Island. Apt because it is prolifically populated by four foot long Monitor Lizards, locally called Goannas. Lizard Island, with its close neighbours Palfrey and South Island, is a granitic remnant of some vast and long gone volcanic eruption. The highest point on Lizard Island is about a thousand metres above sea level and it is reportedly this peak to which Captain Cook climbed to see his way out from within the Barrier Reef when he explored the Australian coast in 1770. Between the three island peaks lies a shallow lagoon containing its own mix of habitat, from Mangrove to Forameniferan gravel and from coral bommies to fringing reef. The Island is nine miles inside the outer barrier reef and about thirty miles off the mainland coast of Queensland. Lizard itself is about three miles by four miles and it is home to the Australian Museum of Natural History's marine research laboratory, which is a well run, much patronised field station of considerable merit.

 

I’ve had the privilege of spending more than a year of my life on Lizard over the past sixteen years. Until the last two most recent trips, I did not fully appreciate just how true was that comment to the team. With the knowledge of hindsight, I can say now that every one of the five extended visits to Lizard has brought with it a characteristically different assemblage of oceanic pelagic drifters - and indeed it was the drifters, that huge planktonic biomass of animals and plants - that we were primarily there to shoot. What was exciting about these more recent trips was that we were there to film these beautiful and bizarre creatures not only on the largest film format in the world but also in 3-D. Imagine animals smaller than a pin-head drifting through the auditorium, that seats 500 people, the size of hot air balloons! From a technical standpoint, this was a major challenge. We shipped in excess of eight tons of equipment to do it. But, that is a different story. This account is about just one of the strange encounters we had on the second of the two most recent expeditions.

 

Early in the trip, we were out near the edge of the lagoon reef only a mile from base. The previous night had introduced a wind change from the prevailing South East trades to the more interesting North Easterlies. These winds tend to draw in a warmer water current and with them usually come a more tropical, drifting population. Up to now, by far the most dominant large drifter had been the ubiquitous common jellyfish, Aurelia aurita. No previous trip had ever seen such an overwhelming abundance of these four to five inch jellies. Perhaps the change in prevailing wind would change our drifter.In the water, we were made instantly aware of the changing state of the currents, as we were continually in and out of cold and warm patches of water. In due course, our crude weather-watch rewarded us. Coming through the reef from the North were still a number of Aurelia, but scattered amongst them were a few dozen glassy-transparent lobate ctenophores flashing their iridescent comb plates and for all the world looking more like mantelpiece ornaments than animals. These were Mnemiopsids. Like most comb jellies, Mnemiopsis is generally a microfeeder. There are accounts however, of small fish being taken by this comb jelly which as an adult can be four to five inches long. We certainly have seen this comb jelly capturing half-inch long shelled pteropods which remained clearly visible within the attacker for hours to follow. More usually however, lobates are microfeeders. Typically they ensnare their prey in streams of mucus which are then wafted into the oral grooves by beating cilia. Copepods, crab larvae, mollusc veliger larvae and a host of decapod shrimp larvae are the most common victims.

 

On this particular day, scattered through the population, were a few pale purple hydromedusae - in this case Aequoria. Noticeably they were a bit ragged - they had obviously weathered a storm or been nibbled by sergeant-major fish or possibly even been damaged coming through the outer barrier. We were frustrated, because it was these that were one of our principle shooting subjects and their poor condition ruled out any filming. Nonetheless we collected both the lobate ctenophores and the medusae and were beginning to think of returning to base when we suddenly spotted something new. About the size of a fist and cobalt blue in colour, abreast our boat drifted a ragged looking jellyfish. A scream, a polythene bag and a splash later, we had the beast bucketed and on board. Against the white of the bucket, it appeared a bit pinker, but it was strangely messy to look at. It was actively alive but rather flaccid. Only then did I notice that entangled amongst the tentacles was what looked like a small Aequoria. Later in the day, that observation was to trigger a thought that in due course would turn out to be spectacularly true. The term hydromedusan is applied to jellyfish that spend part of their lives as hydroid-like polyps on rocks and beneath overhangs. Aequoria is seldom seen as a polyp but somewhere round the reef it must grow in great carpets. The medusa phase builds up into huge numbers in the late summer and they must all have come from polyps.

 

We now could broadly identify our new found acquisition. It was a Lion's Mane jellyfish of sorts. The genus was Cyanea, but the species was definitely not capillata - the big orange Cyanea. Possibly this was Cyanea lamarcki, which off our coasts is usually considered a more southerly species. The Lion's Mane jellyfish is usually considered to be the largest in our oceans. North sea individuals around our coasts may be 2 feet in diameter and have tentacles 40-50 feet in length. In the Arctic Ocean, Cyanea capillata has been recorded 6 feet in diameter with tentacles fully extended up to 60 feet. Such a jelly would weigh more than a quarter of a ton - 99% of it water! Most of us seldom see Lion's Manes with extended tentacles, but on one of our previous trips to Lizard Island, we had taken a boat across to the mainland and there, in no more than 7 or 8 feet of water, we had encountered a number with tentacles streaming out in the current like a great cream- coloured pathway behind them. As soon as we entered the water, they had withdrawn the tentacles to the more familiar 2 or 3 feet.

 

We returned to base, refreshed water in buckets and retired our catch to the shady cool of the tank-room. While we changed, grabbed a quick lunch and prepared to do photographic justice to our soft-bodied coelenterates, I wondered how on earth we were going to cope with such active creatures. Uncharacteristically, for this trip we had come partly prepared! A month or two before departure, we had engineered a pre-fabricated tank system that we hoped would enable us to set up in the relative control of the laboratory tank room. We were about to put the system to its test.

 

We began by transferring about a dozen Aurelia into the tank, followed by one small Cephea that we had also caught. Finally we introduced the Cyanea. As the different individuals sorted themselves out and began to respond to the current within the tank, it was noticeable that the Aurelia and the Cephea still looked like smoked glass, but the Cyanea now appeared a beautiful pale salmon pink colour. The slightest current would waft the tentacles all over the place. The very frilly edges to the lips of the mouth were like a silky Victorian bedspread, all convolutions, pleats and tucks. As the bell rather lazily pushed its owner around the tanks, this voluminous skirt of lips and tentacles flared and pencilled in response.

 

Every now and again the skirt or a tentacle would brush across an Aurelia. It was very noticeable that the tentacles were either very sticky or firing off nematocysts when this contact was made. For some hours we watched the activity of the jellyfish and we closely monitored the tank, its flow and its seams! Tanks are always tricky and those prefabricated eight thousand miles away are worse than most! Needless to say, a small leak did appear but an adjustment to our cramping system sorted that one out.

 

While we were engaged in this spell of animal husbandry, I thought back to when we had caught the Cyanea. I remembered the small Aequoria in its tentacles and I began to theorise as to why a jellyfish with a goodly sting (personal experience of Lion's Mane jellyfish!) would have such a voluminous skirt and why it was so sticky towards other jellyfish. Could it be that this was a jellyfish-eating jellyfish? Within an hour of that thought, we knew the answer.

 

After a number of "sticky" encounters with the Aurelia in the tanks, our pink Cyanea bumped more forcibly into a common jellyfish nearly twice its size. This time several tentacles and plenty of the skirt came into contact and this time they stuck firm. Within two or three minutes the embrace was secure and as we watched, an insidious process began. Those frilly lips on the skirt that had initially swaddled the Aurelia pulled back and in their place four transparent, much more simple flat lobes began to flow over the surface of the Aurelia's bell. These were the lips proper. The frills were just extensions of the mantle and seemed to be more sensory in function, whereas these were obviously more gastric. Here was the beginnings of a gargantuan swallowing act. Within a further few minutes the lips had well and truly embraced the bell of the Aurelia.

 

Two hours it took for the Aurelia to be fully ingested and nothing other than a mucus-covered core of tissue to be let drop to the bottom of the tank. For the three of us who had laboured so long to prepare the tanks and get the flow system set appropriately, it was a fitting experience and all credit should go to Justin Peach and Chris Parks for their efforts to overcome the numerous technical difficulties which accompanied their efforts to help us collectively achieve the tank system that made possible the photos in this article.

 

What we didn't know at that stage was that a month later we were going to catch another Cyanea whose activities were going to eclipse those we had just witnessed. On this occasion we caught Cyanea in the deep water channel and again we had plenty of Aurelia available. Every day of our three month trip was characterised by seeing huge wind-rows of these jellyfish, we must have seen millions throughout the trip. Again the catch was made before lunch. This time, before we grabbed a bite and changed, we put the Cyanea in a very large holding tank in which there were only a sea hare and a couple of medium-sized upside-down jellies (Cassiopea) lying in characteristic fashion on the bottom of the tank. They were fine - no Cyanea would scrabble around on the bottom. How wrong can you be? Within six hours both Cassiopea had been caught, digested and their remains spat out!

 

We were staggered. We transferred the Cyanea to the filming tank and introduced several Aurelia. Within four hours two of those had been also devoured and our photos show that the Cyanea actually coped with them both at once. In ten hours our Cynea had completely destroyed four jellyfish larger than itself!

 

There is no doubt, in our minds, that Cyanea lamarcki, (if that is its name), is a most effective jellyfish cannibal.

 

IMAGE QUEST is supplying this to you on a strictly confidential basis. The contents is original material by PETER PARKS and incorporates some facts new to science.

 

We request that permission is sought from the author before materials are in any way commercially used or exploited.

 

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