MARINE NATURE NOTES

Otago Daily Times, Issue 22422, 17 November 1934, Page 5

MARINE NATURE NOTES

Written for the Otago Daily Time*. By David H. Qbaham, F.R.M.S., : F. 2.5. JELLYFISH. Jellyfish are usually looked on as •visitors to Otago water during the late summer months when the temperature of sea is considerably warmer. They | are then found stranded on our beaches. Last Monday, however, two small specimens -were posted to me from Brighton .for information as to their methods of feeding, and more particularly as to of stinging. Of jellyfish in general I may say that, though they are said to be denizens of the temperate and tropical seas, they are also inhabitants of the frig’d waters. One remarkable point in relation td those found in cold seas, as compared; with/to while the jellyfish , found in Otago waters are generally dull and obscure, those found further north and in the torrid zone appear in all the splendour of tropical Colours. 'The land has its flowers blooming ia our 'gardens, over the countryside and in the bush, but the ocean also has its flowers, and the jellyfish with its wonderful purples, goldenyellow and ruby-red tints adorn ‘and ornament the eca in sunny' regions. There are few more beautiful sights than to sit in a rowing boat and watch jellyfish passing in shoals through the water, pulsating as if the whole being were but* a transparent heart, with their delicate fringed tentacles trailing behind, and now and again rolling over as if in the joy of living. • The body of the ordinary jellyfish as found on these shores is a transparent, jelly-like bell, decorated at the edges with long stinging tentacles. In tffe middle of the undersurface is the mouth, which is surrounded with larger * tentacles and generally at the end of u short tube that droops down like the handle of an umbrella. If at any time anyone wishes to watch the pulsating of ‘ the jellyfish, let me advise him to place one in a :basin ol sea water. Living specimens sdiicli I hays[ kept in captivity gave me a great deal of interest and instruction, for each one can bo observed to beat rhythmically almost like a heart. Each; beat consists of a* simultaneous contraction of the. whole of the creature, which has the peculiar effect of raising the'iianiaal upwards through the water. After each beat the bell or disc expands again. This is on account of its elasticity. The Contraction is brought about hy a layer of iinuscleS in the disc dr hell. Those kept in captivity sometimes heat slowly and sometimes quickly, and •at other times do not appear to beat at all as though they are resting. Whenever t have been watching these anima’s in their natural habitat they appeared ;to heat more rapidly than when kept in “captivity. It is this strange beating movement that gives , the jellyfish its method of progression through the water. V The jellyfish bell is nothing more or less than an arrangement of nerves and muscles, and there is only one answer to all. the, questions .which are put to, it: • It can pulsate, it can vary the pulsating by pulsing or beating more strongly or more slowly and that is all. The nervous system of the jellyfish may be compared to a telephone system, where only ,a’ tangle of wires is the result. The raising of one receiver would call up hundreds of subscribers, or,, if one spoke loud enough, -every subscriber in the •system. It will" be seen, therefore, how lowly the hand how wonderful to find an. animal • made.'up almost entirely, of water, and shrink to ; a mere nothing when doned. When iii Auckland, where .larger i, be found washed ashore,. I haye-often secured; half a hundredweighfcCof them and placed : the -lot in- ■ a punctured cask, with fine holes to allow, drainage,, whore the sun could i/ strike on them. Within a few days all that was left was a light varfiish. All ■ the rest had been absorbed by the sun or drained away. . ‘ My observations show that these watery animals have the power to swim .on the surface or,sink to lower depths. At times when the weather is calm and the sun is shining, the surface of the water may be seen with thousands of moving jellyfish, but as soon as the sky becomes : stormy looking, the temperature drops, and the jellyfish sink to more tranquil depths defore the waves become too rough. The jellyfish, in spite of its watery nature and its beauty, is in reality a ,voracious carnivore. It seizes it* prey (which may be anything from minute worms to small fish) by means of the long, trailing tentacles which, like the sea anemones’, are armed with stinging batteries of minute nettle cells. Each cell carries a tiny, micro/icopic bag filled with a fluid, and at the same time draws out into a whip-like process which lies coiled within this tiny bag. Now when any animal touches these tentacles and nettle cells, tbe cells explode and the thread, which is bailed, is shot violently out and into the body of whatever' animal touched it. Vv’hat is the result? The animal is pricked by the'barbed thread which has been lying in the Lag in a poisonous fluid, and when some of this enters the wound a paralysis takes place. The prey is then pushed into the mouth and moved into the stomach, where it is digested with remarkable speed. In captivity these jellyfish have' been seen by the writer to wallow small fish three inches in length, after having first caught them with their delicate and inoffensive looking tentacles. It is said that jellyfish can seize animals much larger than themselves, and,.after playing with tnem its an angler does a trout, swallow and digest them at their leisure. It is these small barhed needles or threads that produce that burning sensation when a bather comes in contact with them. These mushroom-like animals with their delicate tentacles, insignificant as they, may appear, are formidable weapons against all minute or even larger animals with which they come into contact. While jellyfish consist for the most part of water, and may appear of no immediate use to man, indirectly their services are not to be despised, for they serve to nourish the colossal whale. My experience shows that they also form part jof the food of the sunfish, and makes me wonder how many of them a fish of these huge dimensions would have to swallow to obtain a small amount of nourishment. It seems doubtful if the jellyfish that inhabit our shores contain sufficient potent poison in them stings to produce serious results. That certain kinds in other parts are dangerous is quite true, and one often finds support to this in overseas papers where a jellyfish has produced valvular „■disease of the heart directly caused by the poisoning of the stings. Here in New Zealand, more . especially in Auckland, bathers swim in and out amongst shoals of jellyfish so abundant that they are touolrng them the whole time. I have often been swimming in Auckland with children and encountered these animals all the time we were in the water without even a stinging sensation. To seme, however, the touching of a jellyfish with the skin produces a sting not unlike a nettle, and at times raises blisters similar to those produced by this plant, but for the most part they may be handled with impunity.