Karen Boswarva looks at the science behind the defensive / offensive mechanisms of jellies visiting her Orcadian shores
OCEANSCIENCE
The speed of a sting
Karen Boswarva looks at the science behind the defensive / offensive mechanisms of jellies visiting her Orcadian shores
Summertime. The late hazy sunsets far out west. Seabirds filling the cliffs and skies, laden with juicy sand eels. A glistening, calm sea bursting with life and itching to be explored. Getting in the water has never felt so good!
As you walk along the shore, small gelatinous blobs deposited on the ebbing tide appear to melt into the sand. They are vast and colourful, capturing light like stained glass, shining bright blue, purple, or copper. Some have fluorescent pink rings, others display the remains of long, thick frills or tendrils. We are curious, getting as close as we dare, yet scared to touch for we know what these formidable creatures once were.
A SEEDS( safety, equipment, exercise, discipline and signals) brief in summer will include some forgotten essentials. You’ ll be told to drink plenty of water, wear sunglasses, sun cream, and a hat! You’ ll also be warned of jellyfish. The tendrils of lion’ s mane have a habit of attaching to shot lines and finding that one tiny bit of exposed skin between the lips and nose( yes, my eyes teared at the memory too).
Jellyfish belong to a big group of animals called Cnidarians( silent c). This includes all anemones, sea fans, sea pens, and hydroids. Their common trait is that they all possess stinging cells called nematocysts.
Nematocysts are cells produced within the Golgi apparatus, the packaging centre of a cell. The specialised cell or nematocyte is a secretory product comprising peptides, proteins, phospholipids, glycoprotein, sterols, bioactive amines and carbohydrates. These nematocysts are mainly used for defence and capturing prey but can also be used for locomotion.
Despite large variation in size and shape, nematocysts share a common design. A cylindrical capsule with a long, hollow thread attached. The thread is inverted and coiled within the capsule, sometimes armed with spines and ready for the attack!
A slight chemical or mechanical stimulus is all that’ s needed and the thread expels like a harpoon, driven by hydrostatic pressure of 15 megapascals( that’ s 150 ATM!). The pressure causes the tubercule( thread) to invert and expel at an acceleration of up to 40,000G! That makes it one of the fastest known biological processes. To compare, the mantis shrimp, renowned for its speedy punches, reaches 10,400G per clout, the equivalent acceleration of a. 22 calibre bullet.
Parcels of toxins – the painful part – located outside the capsule are attached to the threads just before release. The delivery of toxins into an animal’ s tissues stuns or kills prey and give predators a nasty surprise.
“ Approximately 150 million people per year are exposed to jellyfish stings”
Human skin is thick with many layers, some thicker than others. This barrier helps to protect us from the larger nematocysts. It’ s why the tenacles of an anemone feel sticky( if you’ ve ever touched one). The smaller toxin-filled harpoons can get through our skin cells though, causing mild to severe reactions from burning and itching sensations, redness, swellings, and sometimes even death.
Approximately 150 million people per year are exposed to jellyfish stings, most with nothing worse than a good story to tell after. Scientists are still trying to create an effective barrier for those who work and play in the sea, a super-hydrophobic surface to act as a nematocyst repellent. The tricky part is getting a hydrophobic substance to stay on the skin when submerged in water. So, any engineers reading this, get your thinking caps on!
Some animals have cleverly adapted, using nematocysts for their own benefit. Species of nudibranchs feed on cnidarians to steal their toxins, incorporating them into their own tissues as protection, a process called kleptocnidae. A genius way to avoid predation.
It may sting to admit it, but you’ ve got to admire these fiery wee beasties of the animal kingdom. �
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