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or into empty cargo holds when offloading cargo, and is protected areas are leading to an increase of marine
discharged when loading cargo or bunkering (fuelling). introductions into many MPAs, with severe ecological
Ballast water therefore consists mostly of port or near-port impacts on biodiversity in some cases.
waters that can contain many viable alien organisms even
after long voyages. After these organisms are flushed into Less obvious, although considered the third most important
a new port environment, some of them may begin to source for the introduction of alien aquatic species, are
crowd out native species and disrupt local ecosystems. aquarium and ornamental escapees (IUCN, Lowe et al.,
2000). The dumping of unwanted organisms, escapes from
Shipping is also an important vector for secondary
tanks and breeding farms, the drainage of water containing
introductions — the dispersal of an alien beyond its
organisms from tanks and public aquariums and the direct
primary location of introduction. The widely invasive algae
release of unwanted pets are activities that can bring alien
Caulerpa taxifolia and Caulerpa racemosa var. cylindracea
species into the marine environment. A good example of an
were spread across the Mediterranean by ships, fishing
aquarium species turned invasive is the killer alga Caulerpa
boats and recreational craft. Several Red Sea aliens such
as the mussel Brachidontes pharaonis have also spread taxifolia, an alga that now continues to spread through the
as far west as Sicily in ship fouling. Additionally, shipping Mediterranean.
trade routes have ensured that the Mediterranean exports
biota as well as importing it: the Indo-West Pacific portunid Ports and small marinas act not only as gateways for alien
crab Charybdis hellerii, which has been present in the species but also as reservoirs. They can produce a constant
eastern Mediterranean since the 1920s, has been spillover of new invaders into surrounding areas, where MPAs
transported in ballast tanks to Latin America, and other may be located, and thereby contribute to their successful
species such as the veined rapa whelk, Rapana venosa, establishment.
native to the Sea of Japan, have spread to the Aegean and
Adriatic Seas, possibly by larval transport in ballast waters The growth of marinas in many Mediterranean coastal areas
from the Black Sea. in recent years could be providing a platform for the spread
of invasives as these sites are closely associated with the
Mariculture movements of vessels (fishing or recreational boats or

The increasing market-driven demands for exotic fish and commercial ships) carrying alien species as hull fouling.
shellfish and the decline in wild fisheries have created a surge Although antifouling paints help to control fouling, hulls are
of marine aquaculture (mariculture) along the shores of the still an important means of transport for invasive species.
Mediterranean in the last 30 years. Production of shellfish has
increased exponentially, and two commercially important Likewise, small fishing and recreational boats clearly have a
shellfish, the American oyster Crassostrea gigas and the high potential for spreading marine organisms. On arrival,
Manila clam Ruditapes philippinarum, were intentionally transported alien species may release gametes that
introduced into the Mediterranean for this purpose in the successfully colonize new areas or they may be discharged
1960s and 1970s, respectively. from boats and their fragments may re-grow, establishing
new populations. Fishing gear, bait products, propellers and
Unrestricted transport of commercially important alien anchors, recreational equipment such as scuba-diving gear,
oysters has also resulted in numerous unintentional and other types of commercial fishing tools have also been
introductions of pathogens, parasites and pest species.
Oyster farms have served as gateways into Mediterranean implicated in the transport of non-native fauna and flora.
coastal waters for other associated species as well as
several non-native algae. At Thau lagoon, for example, the
spread of the brown alga Sargassum muticum has locally
displaced the native alga Cystoseira barbata by blocking
light penetration and thus inhibiting the growth and
recruitment of the native species. Similarly, the slipper
limpet Crepidula fornicata, native to the Atlantic coast of
North America, also arrived with culture animals in the
mussel beds near Toulon (France) in 1957. Parasitic
copepods, such as Mytilicola orientalis and Myicola
ostreae, and the toxic dinoflagellate Alexandrium catanella
are examples of associated alien species introduced into
some areas that may render commercial molluscs and
other species unfit for human consumption.
Other pathways by which aliens enter
MPAs
There are also multiple other vectors or pathways that can
bring invasive species into MPAs. Increasing maritime traffic,
visits by recreational boats and aquaculture farms in or near Izola port, Slovenia. Photo: M. Otero

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