Last week we observed a Spotted sea hare (Aplysia dactylomela) depositing a string of eggs. This is quite a special sight and a great opportunity to share some interesting facts about this rather fascinating sea slug. First of all, the Spotted sea hare is a simultaneous hermaphrodite, which means that it has both male and female reproductive organs and can act as either sperm donor, sperm recipient or both (1). In fact, when two Spotted sea hares mate, they can switch roles between sperm donor and recipient (2). You might even observe entire chains of mating sea hares! But enough about sea hare copulation now.
Spotted sea hares secrete a purple, very toxic and distasteful ink when they feel threatened. Both seagulls and scavenging crabs, who would normally devour a good piece of sea hare or baitfish, rejected those tasty treats as soon as sea hare ink was present in the water (3,4). The purple pigment is derived from red algae (5). And speaking of a balanced red algae diet - it is also important for their offspring. Sea hares make their own sunscreen in the form of (Mycosporine-like) amino acids, which they obtain from red algae.The more red algae they eat, the more natural UV protection is present in their spawn (which is the spaghetti-like gelatinous string on the photo that can contain up to 83 million eggs!) (6).
All in all sea hares live a short but fervent life that usually ends after less than a year, during which they mate in chains of up to 30 individuals, lay up to 41.000 eggs per minute and fend off predators with purple poison.
References
(1) Lederhendler, I., Tobach, E. 1977. Reproductive roles in the simultaneous hermaphrodite Aplysia dactylomela. Nature 270, 238–239.
(2) Zaferes, A., Skolnick, A., Tobach, E. 1988. Interindividual contact and copulation in Aplysia dactylomela, Marine Behaviour and Physiology, 13:3, 221-238.
(3) DiMatteo, T. 1981. The inking behavior of Aplysia dactylomela (Gastropoda: Opisthobranchia): Evidence for distastefulness, Marine Behaviour and Physiology, 7:4, 285-290.
(4) DiMatteo, T. 1982. The ink of Aplysia dactylomela (Rang, 1828) (Gastropoda: Opisthobranchia) and its role as a defensive mechanism, Journal of Experimental Marine Biology and Ecology, Volume 57, Issues 2–3, Pages 169-180.
(5) Arruda Bezerra, L.E.,Urano Carvalho, A.F., Aires Barreira, L., Rodrigues Nogueira, V.L., Feitosa Silva, J.R., Vasconselos, I.M. 2004 . The relationship between seaweed diet and purple ink production in Aplysia dactylomela rang, 1828 (gastropoda: opisthobranchia) from Northeastern Brazil. Journal of Shellfish Research, vol. 23, no. 2, 581- 584.