The Transfer of Harmful Aquatic Organisms and Pathogens with Ballast Water and Their Impacts - Global Maritime Transport and Ballast Water Management: Issues and Solutions - page 47

fi lter-feeding molluscs toxic. However, there are national programmes that regularly
monitor for these toxins to ensure that both cultured and wild molluscs are safe for
human consumption. Sudden outbreaks of toxic dinofl agellate species have taken
place world-wide and have been attributed to ballast water releases (Hallegraeff
1993 ; David et al. 2007 ). On occasion their occurrence and also collapses of
blooms of non-toxic species can cause de-oxygenation events to result in losses to
aquaculture production, fi shery landings and high mortalities of bottom living spe-
cies. Although monitoring programmes exist, human casualties are also reported
each year due to consumption of toxin contaminated seafood and it was found that
ballast water and the sediment contained in the tanks, are one of the main (if not
the main) transfer vectors of potentially toxic dinofl agellates (Hallegraeff 1993 ;
David et al. 2007 ).
Transfer and Impacts of Cryptogenic Species
There are many species whose status is unclear because they may be native species
that have recently been recognised or undergone an outbreak and their native range
is not clearly known. Those species not demonstrably native or introduced are
termed cryptogenic species (Carlton 1996 ). There are several examples that include
the fouling brackish water barnacle Balanus improvisus , the bivalve Mya arenaria
and the ship-worm Teredo navalis . Due to the taxonomic uncertainties many phyto-
plankton species (i.e., dinofl agellates and diatoms) are seen as cryptogenic species
as many are now known from many different world regions and their identifi cation
is often a highly specialised skill, improved in recent decades using new technolo-
gies (Gómez 2008 ). This group of species is of special concern as many are poten-
tially toxin producers which affects many resource users (see above).
Mya Arenaria
Already the Vikings sailed the seas and their activities may have resulted in the
introduction of the North American bivalve Mya arenaria to Europe (Petersen et al.
1992 ). It was suggested that Vikings when returning from North America may have
kept live Mya arenaria onboard either intentionally as fresh food, or unintentionally
may have imported them with the solid ballast on their vessels. Excavations at
Haithabu, Germany, a Viking trade hub in the Baltic Sea, revealed enormous num-
bers of ballast stones at and near the landing pier (see Fig. 4 ), supporting the
probability of a species introduction with this solid ballast.
Viking ships are likely to have explored sheltered estuaries in North America,
and these environments would likely have had large numbers of Mya arenaria .