I have not completely abandoned
my blog although it certainly looks like it. I have so much respect for people
that maintain blogs whilst travelling as you
get so caught up doing things that things like this take a such a low priority.
Excuses aside, I will try to be more consistent.
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| The Portuguese Man o' War from Stradbroke Island |
Portuguese Man o’ War
The idea for this blog came from
a beach on Stradbroke Island. I was walking along and came across a small blue
jellyfish that had washed ashore. I recognised it as a Portuguese Man o’ War,
commonly known in Australia as a ‘bluebottle’. It immediately reminded me of a
lecture from 2nd year that taught me that this particular species of
jellyfish is not a single organism. It is in fact not a common jellyfish but a
siphonophore, a colony of highly specialised, minute individuals called zooids,
which make up a fully functioning animal. These zooids are physiologically
assimilated and work in unison to function as a single organism. Zooids are so
reliant on each other to function that they are completely incapable of
independent survival. The Portuguese Man o’ War is composed of 4 separate
entities: the sail (pneumatophore), defense (dactylozooid), reproduction
(gonozooid) and feeding (gastrozooid).
The jellyfish generates carbon monoxide from a gas bladder to help
inflate the sail along with other gases (Nitrogen, Oxygen and Argon) which
diffuse into the gas bladder, allowing floatation. The sail itself is capable
of deflation in the event of a surface attack allowing temporary submersion to
avoid a potential predator. The long tentacles that protruding from the base of
the sail are normally 10 meters long but can be as long as 50 meters. These
tentacles each contain stinging cells known as nematocysts (I will go into more
detail about them later). These venom-filled stingers fish below the jellyfish
and kill small sea animals. Contractile cells within the tentacles then
manoeuvre the prey to the gastrozooids for digestion via enzyme secretion.
Although a sting is not fatal to humans, they do cause severe pain and skin
irritation (as David found out at Manly beach a couple of weeks ago).
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| A much larger specimen. indicated are the various Zooids that make up the Portuguese Man O' War. |
The life of a
jellyfish
A heading like this is unlikely
to suggest major excitement however jellyfish are actually sexually reproducing
carnivores....that just unfortunately look like a floating plastic bag. Their
reproductive cycle is pretty cool though. Firstly, the male and female expels
sperm and eggs into the water column whereby they unite and form a larvae
(known as a planulae). Each planulae will drift until they settle on something
solid on the ocean floor. The planulae anchor themselves into position and
continue their development into fixed polyps. Polyps themselves can reproduce
asexually (refresher on asexual reproduction http://stannagescience.blogspot.com.au/2015/06/lesbian-lizards-of-south-america.html)
and produce many clones of themselves. This developmental stage can last for
months or even years. It has been suggested that transition into the medusal
stage only occurs when the organism detects that conditions are suitable for
survival of the adult. At which point, the polyp elongates, allowing the mature
medusa to bud off and begin its life as a free-swimming organism.
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| Visual demonstration of the life cycle of jellyfish |
The lifespan of jellyfish is
unsurprisingly short. They tend to live somewhere in the region of a several
hours to a couple of months. Some larger coastal jellyfish can survive up to 6
months but again, being so low on the food chain doesn’t make for an easy
existence. Interestingly, there is an unusual species of jellyfish, Turritopsis gohrnii, which has been
observed to have the capability of reverting back into its polyp stage,
essentially restarting its own life cycle making it effectively immortal.
Imagine growing old only to be able to revert back to being a newborn baby to
begin life all over again.
Obviously, jellyfish do not
possess the complex central nervous system found in higher vertebrates such as
ourselves, however, neural cells within each organism are not just randomly
scattered around. Recent research into the jellyfish neural architecture has
discovered that there is evidence of neural condensation, locations where the
neurons coalesce to form definitive structures. These act as information
centres, taking in sensory information and translating it into an appropriate
stimuli. They do more than just ‘float about’!
The Sting
Jellyfish
are in fact very dangerous creatures. They sting their prey using nematocysts
which are located within specialised cells called cnidocytes, a characteristic
of all Cnidaria. When contact is made with a jellyfish tentacle, millions of
nematocysts are triggered and when they penetrate the skin, high pressure
causes them to burst and inject venom into the victim. Not all jellyfish venom
causes adverse effects on humans however there are many that can lead to fatal
encounters. Most notably by Cubozoa, the
box jellyfish which is well known for causing cardiac arrest and lifelong scars
to its victims. Aesthetically distinct because of their square, box-like bell, these
animals have been named as the most venomous on earth by some scientists.
Researchers have discovered that box jellyfish venom contains porins that
rapidly penetrate red blood cells, allowing potassium to leak out. When the
plasma potassium levels get too high, there is no more electromotive force and
therefore the heart cannot beat. As if that wasn’t enough to keep you well away
from the water, a detached tentacle can still sting you days after it has left
the jellyfish, not to mention the fact that box jellyfish tentacles have been
measured up to 6 meters long!
Conclusion
They
may not be the most exciting animals in the world, but they are fascinating.
They can be beautiful to observe and significantly more intricate to study than
what you would expect. They have been roaming the seas for over 500 million
years and don’t show signs of disappearing any time soon.
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| They're not half bad to look at either. |
Thanks again for reading. Heres hoping it won’t take another
6 months to produce another article!
