- Colour: it has a thin, transparent, upright sail set diagonally on top of a blue flat oval disc containing many air chambers, which keeps it afloat.
- The By-the-Wind Sailor is, in fact, a colony made up of different types of polyps, including some that are specialised for catching food, defense, or reproduction.
- Size: its blue oval disc is up to 5 cm across.
- Diet: small fish and other small marine animals that are caught just below the surface of the water. It doesn't have any tentacles but rather unique stinging cells which trap food as it sails along. The food is moved along to its mouth, which is in the middle of the underside of its disc.
- Movement: it is pushed along the sea surface by wind blowing against the sail on its float, which is angled at 45 degrees to the wind. Some floats are positioned north-west to south-east, while others are positioned south-west to north-east. This means that the same wind will push individuals in opposite directions, preventing all of them being washed up on the shore to die, even if the wind blows some toward the coast.
- Breeding: By-the-Wind Sailors are hermaphrodites (i.e. both male and female). The specialised reproductive polyps release both eggs and sperm into the water. When the eggs have been fertilised by the sperm, they develop into larvae that subsequently metamorphose into individual polyps. A By-the-Wind Sailor colony forms when one polyp divides to form new types of polyps which become specialised for different functions.
What to Observe
- Presence (to establish the first and last sighting of the season)
ClimateWatch Science Advisor
We don't yet know whether water temperature affects where jellyfish are found. Data on their distribution will help determine whether their range is changing and how climate change may impact their distribution.
When To Look
In the warmer months, around summer time.
Where To Look
- In coastal waters around Australia. It is more common on exposed ocean beaches after strong onshore winds have blown it in from the tropical north.
Bennett I 1987. W. J. Dakin's classic study: Australian Seashores: a guide to the temperate shores for the beach-lover, the naturalist, the shore-fisherman and the student. Angus & Robertson.
Davey K 1998. A Photographic Guide to Seashore Life of Australia. New Holland Press, Sydney.
Edgar GJ 1997. Australian Marine Life: the plants and animals of temperate waters. Reed Books.
Nichols D 1979. The Oxford Book of Invertebrates. Oxford: Oxford University Press.
- Blue Bottle Jellyfish (Physalia utriculus): its float is an air sac (not a flat, oval disc like the By-the-Wind Sailor) and it has long blue tentacles which can be up to 10 metres long.
- Blue Button (Porpita porpita): has short tentacles fringing its disc and doesn't have a sail like the By-the-Wind Sailor.
Did You Know?
Its scientific name comes form the Latin word ‘velum' which means a curtain, veil or sail.
It is preyed on by two groups of molluscs of the families Glaucidae (colourful sea slugs) and Janthinidae (purple or violet snails).
Its air chambers keep it on top of the water and it is incapable of being submerged for long.