Floating Jellyfish

All jellyfish float to some extent due to the fact that their bodies are 95% water when they are fully grown, this makes them a similar density to the water and hence allows them to float in the water. There are some jellyfish though which are capable of an amazing feat of floating on the surface of the water; this is not only a peculiar sight but also an interesting ability that the jellyfish possesses.

One such jellyfish is the Velella Velella which is also known as the "By the wind sailor" and "Purple sail" or "Little Sail". This is the most commonly encountered species of jellyfish which floats freely on the surface of the ocean anywhere it wishes to all over the world. These Velella are usually under 7cm in length and are a beautiful deep blue in color and have a very unusual small sail which is rather stiff and is used to catch the winds in order to propel the jellyfish over the surface of the water. In rough wind conditions these "by the wind sailors" can end up stranded in the thousands on beaches. These jellyfish are carnivores and catch their food which is usually plankton by using their poisonous tentacles which hang down in the water below them. These toxic tentacles are harmless to humans. These jellyfish are solely at the mercy of the winds which means they not only have little or no control over their direction but also that they are prone to being stranded.

Another surface dwelling jellyfish is the Portuguese man of war, also known under other names such as the "Blue bottle" or "blue bubble" or just plainly the man of war. The jellyfish is named from a Portuguese war ship style of the fifteenth and sixteenth centuries which was called the man of war. Unlike most jellyfish this one is not just one animal but actually a colony of four kinds of very small yet highly advanced creatures. These jellyfish are well known for being present in blooms of thousands and also for the very painful stings they posses. The float of this jellyfish acts as a sail and the rest of its' body hangs down below the waters surface. This jellyfish has no means in which to propel itself but moves along with currents, the winds and the tides. The Portuguese man of war has a bladder full of air which acts as a sail allowing it to float on the waters surface. The sail is see through with a tint which may be blue, purple or mauve. The sail can be anywhere from 9 to 30cm in length and can be as high as fifteen centimetres above the surface of the water. The jellyfish releases gas into its sail which is of a similar composition to the atmosphere. In order to survive the sail must stay moist and to accommodate this the jellyfish may roll a slight amount from time to time in order to wet the sail. In the event of an attack the sail can be deflated this allows the jellyfish to submerge under the water for a short period of time.

These surface dwelling jellyfish are very interesting to see and can often be found stranded on beaches. To learn more about these species of jellyfish and many other species please visit our Jellyfish Species List Section.

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Written by Nathan Dickerson and Sudarsana Sinha.