EASIN - European Alien Species Information Network

Thread Discussion: Aplysia dactylomela: pathways [thread closed]

Author: Argyro ZENETOS
Created On: 4/16/2014 9:33 AM

Closed On: 8/27/2014 1:21 PM
Closing User: Argyro ZENETOS

Responsible Member(s):
Argyro ZENETOS

Closed On: 8/27/2014 1:21 PM
Closing User: Argyro ZENETOS

Argyro ZENETOS
4/16/2014 9:33 AM

In the MedPAN factsheet (PDF provided by EASIN), three hypotheses are made for the introduction of the species in the Mediterranean: 1) it arrived in ballast water; 2) it spread through the Suez Canal; 3) it spread naturally through the Gibraltar Strait (if this is the case it should not be considered an alien species as such, but a tropical Atlantic species colonizing the Mediterranean through natural range expansion). In EASIN, the species is regarded as alien introduced by shipping. Is there enough evidence to disqualify the other two hypotheses?

Argyro ZENETOS
4/16/2014 10:14 AM

In a recent publication by Valdes et al, (2013) molecular analysis results revealed that all the specimens collected in the Mediterranean have an Atlantic origin. Thus spreading via the Suez Canal as supported by Crocetta and Galil (2012)is to be excluded. The limited sample size does not allow identification of the dispersal pathway of A. dactylomela into the Mediterranean, but the colonization sequence is consistent with a “natural” dispersal event (Valdes et al., 2013). However, as the first introduction event was reported from the central Mediterranean and the species is still absent in the western Med (excepting the 2013 record from the Egadi Islands (western Sicily) (Mannino et al., 2014) the ship mediated introduction cannot be excluded as a pathway. refs Crocetta F, Galil BS (2012) The invasive spotted sea hare Aplysia dactylomela (Mollusca: Gastropoda: Aplysiidae): New records and spread pattern in the Mediterranean. Vie et Milieu 62: 43–46 Mannino et al.(2014). First record of Aplysia dactylomela (Opisthobranchia: Aplysiidae) from the Egadi Islands (western Sicily).Marine Biodiversity Records, page 1 of 4. # Marine Biological Association of the United Kingdom, doi:10.1017/S1755267214000190; Vol. 7; e22 Valdés A., , Alexander J., Crocetta F, , Yokeş Mb, Giacobbe S., Poursanidis D., Zenetos A., Cervera Jl, Caballer M., Galil Bs., Schembri Ps., 2013. The origin and dispersal pathway of the spotted sea share Aplysia dactylomela (Mollusca: Opisthobranchia) in the Mediterranean Sea., Aquatic Invasions, 8, 4: 427–436

Argyro ZENETOS
4/16/2014 10:14 AM

Fabio CROCETTA
4/30/2014 12:58 PM

The current status of Aplysia dactylomela Rang, 1828 is still debated since at present it remains unresolved if its Mediterranean spreading has been a human-mediated or a natural event, even though the second hypothesis seems to be the more likely (Valdes et al., 2013). Therefore, it cannot be listed as an alien with confidence (due to the absence of a certain human introduction). However, it also cannot be listed as cryptogenic (see Carlton, 1996: a species that cannot be included with confidence among native nor among introduced ones) due to its large sizes and unmistakable color pattern, that would not have left it overlooked in the Mediterranean Sea for at least two centuries (therefore also excluding it is a native species). Therefore, in cases as such, where should be it included? Under "questionable" (= its alien status is questionable)?

Fabio CROCETTA
8/27/2014 1:07 PM

This species was left as alien (possible alien) and the pathway remained as shipping, waiting for further molecular data.

Argyro ZENETOS
[Closing post]
8/27/2014 - 1:21 PM

No closing text.

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