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Mediterranean invasive species factsheet

Similar species Ceuta and the Balearic Islands), France (including
Microcosmus squamiger can be confused with the Corsica), the Tyrrhenian Sea (coast of Italy) and
very similar and also alien species Microcosmus Malta. Given its presence in harbours, marinas and
exasperatus. The species differ in some internal aquaculture farms, it is thought to have been
characters, such as the shape of the siphonal introduced in the ballast waters of shipping vessels,
spines, which in M. squamiger are fingernail shaped in fouling on ships and recreational boats, and
and short, while in M. exasperatus they are pointed through aquaculture.
and longer.
Ecological impacts
Microcosmus squamiger can form dense
aggregations (from about 500 up to about 2,300
individuals per square metre) in the shallow
sublittoral zone, closely carpeting rocky areas and
becoming a major structure-forming organism that
colonizes all the available substrate and alters local
native communities. It can be found on natural and
artificial hard substrates, in or close to harbours and
marinas.

Economic impacts
Microcosmus squamiger is considered a pest to
bivalve culture in some areas, where it competes for
food and space. It is also a nuisance fouler on ships,

MIcrocosmus exasperatus recreational vessels and other submerged man-
made structures.

Management options
Strict controls on aquaculture procedures and
transport as well as regulations and management
concerning fouling on commercial and recreational
vessels may prevent further introductions.

Further reading

Rius M. et al., 2009. Population dynamics and life cycle of
the introduced ascidian Microcosmus squamiger in the
Mediterranean Sea. Biol. Invasions 11, 2181–2194.
Rius, M. et al., 2012. Tracking invasion histories in the sea:
facing complex scenarios using multilocus data. PLoS ONE
Microcosmus exasperatus. Photo: Shih-Wei
7, e35815.
Brief history of its introduction and
pathways
Microcosmus squamiger is native to south-east
Australia and has now spread to temperate waters
worldwide. It was first recorded as introduced in the
Mediterranean Sea in the 1960s (as M. exasperatus), Drawings: Juan Varela
and it is now very common around the western
Mediterranean in Morocco, Tunisia, Spain (including

92 AMonitoring Marine Invasive Species in Mediterranean MPAs: A strategy and practical guide for managers