Aplysia punctata, commonly known as the Spotted Seahare, or Dotted Seahare, was first described by Cuvier in 1803. They have a wide distribution and are commonly found around Europe and North Africa. Currently, there are over 1,500 research-grade observations on iNaturalist and over 6,000 from the Global Biodiversity Information Facility (GBIF).

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Key identifying features

Sea hares are very distinctive, particularly when underwater. Their upright rhinophores (sensory tentacles) and broad, oval oral tentacles are clearly visible and give them their common name, as they resemble the ears of a hare.

They also have two large fleshy lobes called parapodia along the sides of their body. These parapodia can be used for swimming and may occasionally allow the Seahare to glide briefly through the water. When the parapodia are spread open, the thin internal shell may sometimes be visible.

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Colour variations

Sea hares show noticeable colour variation, which is influenced by both age and diet.

Juveniles are commonly red in colour, as they primarily feed on red algae. As they mature, their diet may shift towards brown seaweeds, and adults are therefore more often brown. Diet is considered the main factor influencing their colouration.

Overall, body colour can range from red to dark brown and sometimes yellow, often helping them blend in with the algae they are feeding on. Many individuals also have circular or oval light or dark rings or spots across their bodies.

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Reproduction

Sea hares breed during the spring, when their populations often increase noticeably. During this period, individuals can lay thousands of eggs in long, spaghetti-like ribbons.

Sea hares are hermaphrodites, meaning each individual has both male and female reproductive organs. However, they still mate with other individuals to reproduce. During breeding, they often form chains, where one individual acts as a female, another as a male, and middle individuals can act as both simultaneously. These breeding chains can sometimes involve several sea hares lined up together.

After the breeding season, all the adults die, as their maximum lifespan is only one year. The larvae hatch from the eggs and develop through a planktonic stage before settling and growing rapidly. By the following spring, adults can reach lengths of up to 20 cm.

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Similar species

Sea hares belong to the genus Aplysia, which contains several species that can look very similar to one another. Because of this, identification can occasionally be challenging.

The most reliable ways to distinguish between species are by considering their size, overall body shape, and geographic location. Colour alone is not always a dependable feature, as it can vary depending on diet. Sometimes, larger species rely on seeing specific features, such as the rhinophores, while they are underwater, to effectively identify them.

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Predators

Sea hares have a range of potential predators, including crabs, fish, and starfish. However, no species is known to specialise in feeding primarily on sea hares. Instead, they are usually eaten opportunistically and only occasionally. Predators are more likely to consume eggs or juveniles rather than fully grown adults.

Sea hares possess several defence mechanisms that reduce their risk of predation. One of the most well-known is their ability to release a cloud of purple ink when threatened. This ink is both distasteful and mildly toxic to many animals. It can also interfere with a predator’s sense of smell and taste, sometimes causing hesitation or changes in behaviour that allow the sea hare time to escape.

Prey

Sea hares feed primarily on algae, and their diet influences both their growth and their colouration. By consuming green, red, and brown algae, sea hares can match the colour of their surroundings, providing effective camouflage from predators.

Studies have shown that sea hares achieve the best growth rates when feeding on certain algae species, including Sea Comb (Plocamium cartilagineum) and Gutweed (Ulva intestinalis). The body’s ability to change colour depending on the algae consumed helps them blend seamlessly into their environment.

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Occurance Data

For the most up-to-date distribution records, see:

National Biodiversity Network (NBN) - Europe (mostly UK) database of species occurrence

iNaturalist - most up to data records of the species occurrence

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References

Barnes, H.(1963) Oceanography and marine biology. Aberdeen: Aberdeen UniversityPress.

Carefoot,T. H. (1967) Studies on a sublittoral population of Aplysia punctata. Journalof the Marine Biological Association of the United Kingdom 47(2): 335–350.

Carefoot,Thomas H. (1967) Growth and Nutrition of Aplysia Punctata Feeding on aVariety of Marine Algae. Journal of the Marine Biological Association of theUnited Kingdom 47(3): 565–589.

Carefoot,Thomas H., Pennings, S. C., and Danko, J. P. (1999) A test of novel function(s)for the ink of sea hares. Journal of Experimental Marine Biology and Ecology234(2): 185–197.

Sabatini, M. 2008. Aplysia punctata Dottedsea hare. In Tyler-Walters H. and Hiscock K. Marine Life InformationNetwork: Biology and Sensitivity Key Information Reviews, [on-line].Plymouth: Marine Biological Association of the United Kingdom. [cited20-02-2026]. Available from: https://www.marlin.ac.uk/species/detail/2017