Bursatella leachii
Πληροφορίες
This species occurs most commonly in shallow, sheltered waters, often on sandy or muddy bottoms with Caulerpa prolifera, well camouflaged in seagrass beds, and occasionally in harbour environments. If disturbed or touched it can release purple ink.
Its behaviour varies with the time of day, as it is more active during the daytime and hides at night. In the early morning sea hares are found clustered together in groups of 8–12 individuals, and they disperse to feed on algal films during the day. They reassemble again at night.
Bursatella leachii is a hermaphroditic species with a very fast life cycle and continuous reproduction. When mating, one individual acts as a male and crawls onto another one to fertilize it. A large mass of tangled strings of purple eggs is produced and the larvae develop within 20 days. Sexually mature sea hares appear after 2–3 months.
There are no similar species in the Mediterranean Sea. In contrast to Aplysia, Bursatella leachii does not have large mantle flaps and cannot swim. Other species, such as the endemic Tethys fimbria and the genus Melibe, have large oral hoods (ceratas) used in the capture of food and a set of prominent cerata (outgrowth structures) along each side of the body.
Originally found in warm temperate and tropical waters throughout the world, this species was probably introduced into the Mediterranean through the Suez Canal, although ballast waters discharged from cargo ships (water pumped into the ships elsewhere as ballast to adjust buoyancy) could also explain its occurrence in harbours. The first record of the species in the Mediterranean Sea was in Israel in 1940. Subsequently, the species was also recorded from Turkey, Malta, Italy (Taranto, Sicily, Lecce, Naples, Venice, Sardinia), Slovenia, Croatia and around the Spanish coast, including the Balearic Islands and Almería in the Alboran Sea. It has been also reported in the Nador Lagoon (Morocco) and in other coastal lagoons and littoral areas around the Mediterranean.
No studies have yet quantified the ecosystem impact of this species in the Mediterranean. The sporadic high densities reported at some sites and its habit of feeding on microalgal (cyanobacterial) mats may influence the dynamics of some natural habitats.
In its native waters, ragged sea hares can reach very high densities (more than 600 individuals per square metre) and they are believed to adversely affect commercial shrimping operations. Positive economic impacts include the existence of a small aquarium trade for this sea hare and the potential pharmacological use of its ink gland.
Ibáñez-Yuste A., Garrido-Díaz A., Espinosa-Torre F., Terrón-Sigler A., 2012. Primera cita del molusco exótico Bursatella leachii de Blainville, 1817 (Mollusca: opistobranchia) en el litoral mediterráneo andaluz. Chronica naturae, 2: 25-31.
Zakhama-Sraieb, R., Ramzi S., Y Charfi- Cheirkhroucha, F., 2009. On the occurrence of Bursatella leachii De Blainville, 1817 and Pinctada radiata (Leach, 1814) in the Gar El Melh lagoon (NE Tunisia). Aquatic Invasions. Vol 4, Issue 2:381-383
http://www.ciesm.org/atlas/Bursatellaleachi.html
Tanrikul, T. T.; Akyol, O., 2012. First report on reproduction of Lessepsian ragged sea hare, Bursatella leachii (de Blainville, 1817) (Mollusca: Gastropoda) in Izmir Bay (Aegean Sea, Turkey). Journal of FisheriesSciences.com, Vol. 6 No. 2 pp. 96-98.
