Several Geographical Seahares (Syphonota geographica) are clustering together.
The Geographical Seahare is an opisthobranch belonging to the sea hare family (Aplysiidae). Sea hares are usually larger than most species of sea slugs, reaching a total length of approximately 17 cm/6.7 inch. They are green to brown in colour with a cream-coloured marbled patch-like pattern resembling a map, hence their scientific name "geographica." They inhabit inter-tidal zones, shallow seagrass beds, and silty substrates in all tropical areas of the world.
The Geographical Seahare is a nocturnal herbivore that primarily feeds on seagrass species. During the daytime, it buries itself in the sand and substrate. Sometimes the area where it buries itself may become exposed to air as it lies above the low tide line, where the wet sand provides effective protection against the elements, ensuring its survival until the next incoming tide.
Group sex, just like in other sea hares, is not an unusual behaviour for the Geographical Seahare. This behaviour, sometimes called a "daisy circle," occurs when three or more individuals attempt to mate in unison. In such a mating chain, where all individuals are simultaneous hermaphrodites (able to act as both male and female), the first animal in the chain takes on the role of a female, and the last in line acts solely as a male, while all the others act as both males and females simultaneously, either giving or receiving sperm. When large numbers of seahares are involved, the chain can appear as a massive mound.
Sea hare species are also known to swim by undulating their parapodia, which are wing-like structures on both sides of their body. A swimming seahare resembles a mythical flying creature encountered only in fictional stories and fables. Sea hares are among the strongest swimmers among opisthobranchs due to the high position of their parapodia on their back.
The Geographical Seahare may occur in large numbers in a specific spot for a particular period and then not be seen again in that area for several years. These occurrences may be due to specific local conditions. This particular shot was taken at a depth of only six meters during a night dive at Bali's famous muck dive site, Puri Jati, on Bali's northern coast. It was the only time I have ever encountered a large number of Geographical Seahares at a single dive site. When we dived again several weeks later, we weren't able to find a single individual.
Did you notice the two little crabs, one in the lower right corner and another in the lower left corner?
Just like with most of the underwater footage I have collected over the years, the editing process brings the footage to life. For this particular shot, I enhanced the contrast in the images to bring out the marble-like pattern on the skin of these Geographical Seahares. I also increased the saturation of the green colour to distinguish the animal from the darker background and the sand-coloured substrate.
Although there is little action in this underwater videoclip, the footage is quite interesting as it captures a very specific and rarely filmed sea hare mating behaviour: the daisy circle mating chain.
This short underwater videoclip has been filmed in Bali, Indonesia 🇮🇩
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