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VOL. 76 (2), 189-208, 2010 THE IGNORED STOWAWAYS: WORLDWIDE...

maintained by asexual growth constitute the population genetic
structure of many phytoplankton species (26), also exotic genotypes
cold arrive to far regions via biofouling. Some of these non-
indigenous introduced species or genotypes could proliferate in
remote areas and become invasive species.

Long-distance transport of toxin-producing microalgae it is par-
ticularly worrisome. Three harmful microalgae species (Prorocen-
trum lima, Pseudonitzchia pungens and Crysochromulina polilepis
implicated in DSP, ASP and mass mortalities of fish respectively)
were detected in a small area (less of 3 cm2) of biofouling in one
boat. This provides robust evidence on the magnitude of biofouling-
associated transport problem. During the 1950s Margalef (one of the
best phytoplankton taxonomists) analyzed the microalgae species
composition in the Ría de Vigo, NW of Spain, (27-29) providing
extensive list of phytoplankton species composition. However, Mar-
galef never detected several microalgae species that constitutes the
main problem of harmful algal blooms (HABs) in the Ría de Vigo
nowadays. Could have arrived recently these algae to Ría of Vigo via
ships biofouling? Since Ría of Vigo with other Rías of NW of Spain
(i.e. Pontevedra, Arosa, Muros and Lorbé) is the most important
area for shellfish aquaculture in European Union (i.e. mussels, coc-
kles, oysters, clams and scallops) the economic impact of HABs
species introduction of could be enormous.

The key to explain microalgae species transport via ships bio-
fouling is know the mechanisms that allow to these species to sur-
vive long time attached to antifouling paint. Apparently, adaptation
to biofouling paints is not easy. Growth and photosynthetic perfor-
mance of the experimental strain Dc1M was irreversible inhibited by
TBT concentrations many times lower than those used in antifouling
paints. Antifouling paint on the bottom of Nunclon wells-dish plates
rapidly destroyed wild type Dc1M cells. Since adaptation to anti-
fouling paints seems to be difficult, the classic evolutionary point of
view assumes that genetic adaptation at such extreme conditions is
a gradual process (reviewed in 30).

In contrast, here we propose an alternative explanation for adap-
tation of microalgae to antifouling paints. When the experimental
strain Dc1M was cultured in TBT, usually cultures show massive
destruction of the sensitive cells by the toxic effect of TBT. However,

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