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 2½ 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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