Page 77 - Invasive_Species_2013

Mediterranean invasive species factsheet

Similar species late 19 th century, five years after the opening of the
Pteria hirundo is a native oyster up to 7 cm long. It is Suez Canal (1869). Therefore the primary pathway
easily distinguished by its highly irregular shell of introduction was the opening of the canal. Since
shape, in which the valve hinge is straight with two then the species has successfully spread through the
longer asymmetrical lateral ‘ears’. south-eastern basin, while in the western basin it
occurs only sporadically. Commercialization of
The non-native pearl oyster Pinctada margaritifera
molluscs for mariculture and shipping activities are
can be distinguished by its larger size (up to 20 cm),
other reasons for its spread. As larvae can survive in
regular radial ribs arranged in concentric rows and
the water column for up to 30 days, they can also be
greyish green shell with white or yellowish radial
transported in ballast waters, while juveniles and
rows of scales.
adults can be part of the assemblages encrusting
ships’ hulls (fouling).

Ecological impacts
The gregarious behaviour of P. imbricata radiata in
forming extensive oyster beds can modify the
structure of habitats and native communities. It may
also potentially outcompete other filter-feeding native
organisms for food and space. Its broad tolerance of
Pteria hirundo temperatures and air exposure as well as some
pollution, and its expanding distribution earn it a
place among the worst alien species in Europe
(European Environment Agency, 2007).

Economic impacts
These have not been quantified but fouling by rayed
pearl oysters can affect mussel farms. In the Arabian
Gulf, where it is a native species, its economic
impact is positive as it is exploited there for its natural
pearls.

Management options
Suggested prevention measures include conducting
local public awareness campaigns combined with the
monitoring of populations, which makes early
detection possible. Rayed pearl oysters should be
removed from seed bivalves intended for mariculture
purposes. A suggested control action is physical
hand removal of new populations by MPA
technicians.
Pinctada margaritifera. Photo: Jaxshells
Further reading
Brief history of its introduction and http://www.ciesm.org/atlas/Pinctadaradiata.html
pathways http://www.europe-aliens.org/pdf/Pinctada_radiata.pdf
Katsanevakis S, et al., 2008. Molluscan species of minor Drawings: Juan Varela
Originally from the eastern Indian Ocean, Arabian
commercial interest in Hellenic seas: Distribution,
Gulf and Red Sea, the rayed pearl oyster was first exploitation and conservation status. Mediterranean
recorded in Egyptian Mediterranean waters in the Marine Science, 9 (1):77-118.

74 Monitoring Marine Invasive Species in Mediterranean MPAs: A strategy and practical guide for managers