Marine Stingers And Their Deadly Touch

In this blog post I will be covering a mechanism of delivering venom that is a lot different than what has been covered so far. The animals that utilise this method are found in a marine environment, where venomous animals are quite common. There are over 1300 species of venomous fish that occur in the world’s oceans, as well as sea snakes and venomous molluscs such as the cone shell and the blue-ringed octopus. These organisms utilise mostly conventional methods of delivering venom such as spines in fish, fangs in sea snakes, or simply through the saliva in the case of a blue-ringed octopus.

The animals that will be covered in this post, however, are the Jellyfish. They are members of the phylum Cnidaria, which also includes organisms such as hydra and sea anemones. Almost everyone who lives in a coastal area and frequents the beach would be familiar with the sting of a jellyfish, although the severity of the sting depends on the both the species involved and the length of tentacle that has contacted the skin. That being said, many people will stop swimming when they are known to be present. I can say from personal experience that diving under a wave and surfacing with a bluebottle completely wrapped around your face and neck is a fast way to kill a good mood, not to mention the bright red tattoo left behind for a few days. 

While species such as the bluebottle are somewhat painful, they are not dangerous to humans. Venture into the warmer waters of tropical Queensland, however, and swimming during the summer months becomes more dangerous. Chironex fleckeri, or the Box Jellyfish, and species of irukandji make swimming during the summer months a dangerous venture without a stinger suit, or within a stinger net. The box jellyfish can kill a human being faster than any other venomous animal on the planet. A large enough sting can stop a person’s heart in under two minutes. In terms of venomous animals, there are none more potent than the box jellyfish. It is difficult to see in the water, and it is not very big, reaching sizes of up to 25cm across the bell. Symptoms of a box jellyfish sting include immediate severe pain, which may radiate up the affected limb, as well as red or purple tracks where the tentacle touched the skin, and cardiac arrest can occur within minutes from a large enough sting. There is an effective antivenin for the box jellyfish, however, which is more that can be said for the next species of dangerous jellyfish. 

The whip-like tracks of a box jellyfish sting.

Irukandji jellyfish, of which there are four species, also inhabits the waters of tropical Queensland. The species that will be covered in this blog post is Carukia barnesi. It is tiny, and almost invisible in the water, making it far more difficult to detect in comparison with the box jellyfish. It can also make its way into stinger nets, moving unseen through the gaps in the netting. The sting of an irukandji cannot kill as quickly as the box jellyfish, however the aftermath is far more painful.  The sting does not cause undue pain immediately, however after 20-30 minutes, what’s known as irukandji syndrome sets in. Symptoms of the irukandji include nausea, severe headaches, cramps and lower back pain, chest and abdominal pain, anxiety, and can cause tachycardia and a pulmonary edema. These symptoms can last up to 30 hours, and may not completely go away for 1-2 weeks. There is no antidote to the venom of an irukandji, and painkillers do not seem to work with victims. The only option left is to deal with the pain until it abates.

The size of the Irukandji makes it almost impossible to see in the water.

 

So how can these seemingly simple animals be so deadly? We know they sting using their tentacles, but they aren’t like any other venom delivery system we've covered so far. Being able to see something with the naked eye makes it more tangible, and less frightening. The unknown element is always the scariest, and the way that jellyfish deliver their potent venom seems to play on this fear, especially since all it takes is to be brushed by a tentacle for the venom to enter your body. The venom is delivered through specialised cells known as nematocysts, often simply referred to as stinging cells. They consist of a capsule containing a coiled up hollow tube under great tension, surrounded by a stiff membrane. When the cell fires, the coiled tube inverts and springs out of the cell at high speed. It then penetrates the skin of the victim and delivers venom through the hollow tube. Nematocysts are a defining characteristic of Cnidarians, and are only present in this phylum.

Each tentacle of the box jellyfish has up to 5000 nematocysts, so it is easy to see how being brushed by a tentacle can be so dangerous. While touching a tentacle will cause the nematocysts to fire, they are not in fact triggered by touch. Instead, they are triggered by chemicals present on the skin of the victim. This is an adaptation to preserve energy by preventing unnecessary firing of the cells, as nematocysts can only be fired once, and are energy-expensive to create. The actual mechanism of activation involves the sudden release of calcium ions into the cell. This creates substantial osmotic pressure, at which point water rushes into the cell, inverts the coiled tube and the cell fires. This all takes place in a few microseconds.

This diagram shows the pahses of the firing nematocyst.

We have now read about the characteristics of two of the most dangerous jellyfish, but we have not yet learned how it is that nematocysts actually evolved in cnidarians. This is exactly what will be covered in the next blog post.

 SOURCES:

 Mini-Collagens in Hydra Nematocytes 1991
EvaM.Kurz, ThomasW.Holstein, BarbaraM.Petri, JiirgenEngel and Charles N. David - Accessed 15 April 2014


http://animals.nationalgeographic.com.au/animals/invertebrates/box-jellyfish/ - Accessed 15 April 2014

http://www.biosci.ohio-state.edu/~eeob/daly/nematevolution.htm- Accessed 15 April 2014

http://health.nt.gov.au/library/scripts/objectifyMedia.aspx?file=pdf/26/02.pdf&siteID=1&str_title=Box%20Jellyfish.pdf- Accessed 27 April 2014



Images:
http://en.wikipedia.org/wiki/Irukandji_jellyfish  - Accessed 2 May 2014
http://local.brookings.k12.sd.us/krscience/zoology/webpage%20projects/sp11webprojects /boxjellyfish/boxjellyfish.htm - Accessed 2 May 2014
http://www.csulb.edu/~zedmason/emprojects/charlie/moffet.html - Accessed 2 May 2014