BSEP116B Biodiversity in the Baltic Sea - Helcom

Table 6.7.1. Examples of ecological impacts caused by Ponto-Caspian invasive species in the Baltic Sea,
inland European freshwater bodies and North American Great Lakes (modified and completed from Ojaveer
et al. 2002). Species included: Cordylophora caspia (brackish-water hydroid polyp), Cercopagis pengoi (fishhook
water flea), Chelicorophium curvispinum (brackish-water amphipod), Hemimysis anomala (mysid
shrimp), Dreissena polymorpha (zebra mussel), and Neogobius melanostomus (round goby).
Function/Species
Brackishwater
polyp
Fishhook
water flea
Brackish
water
amphipod
Mysid
shrimp
Zebra
mussel
Modifies rocky bottom or
X X X
sediment substrate
Provides shelter from predators X
X
and currents
Traps and accumulates organic X X X
particles from water
Increases water clarity (= lowers X
X
amount of particles)
Affects large aquatic plants X X
Redirects energy from water to X X X X
bottom or vice versa
Provides prey to plankton- and/
X X X X X
or bottom-eating fish
Provides food for waterfowl X X X X
Excludes competing species X X X
Increases soluble (bioavailable)
nutrients
X
Round
goby
(fish)
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From this point of view, the most unwanted alien
invaders in the Baltic are (1) fishery disrupters, (2)
fouling organisms, and (3) boring species. Impacts
of fishery disrupters are anticipated but not yet
proven. The recently detected comb jellies (Mnemiopsis
leidyi and Mertensia ovum) are now abundant
in parts of the Baltic Sea. The American comb
jelly Mnemiopsis leidyi likely contributed to the
collapse of Black Sea commercial fisheries in the
late 1980s, and a similar collapse in the Caspian
Sea in the early 2000s. Fouling organisms such as
the Ponto-Caspian water flea Cercopagis pengoi
cause clogging of gillnets. The zebra mussel Dreisspace),
changes in habitat (physical and biological),
changes in the trophic web, toxins produced
by alien algal species, introduction of new disease
agents and parasites (or introduction of a species
that is a missing link as host in the life cycle of
a parasite), genetic effects on native species
(hybridization, loss of native genotypes), and, as
a worst-case scenario, extinction or drastic reduction
of native species. In this way, it is possible to
distinguish between the types of impact but not
to assess the scales of impact; much remains to
be explored in the field of invasion biology.
In the most heavily invaded coastal lagoons of
the southern Baltic, several food chains and even
major parts of sea-bottom communities may
be based on introduced species (Leppäkoski et
al. 2002). In these areas, the impacts related to
bottom-living alien animals are relatively well
understood (Table 6.7.1), while there is much to
learn about the ecological roles of planktonic
invaders, such as the fishhook water flea (Cercopagis
pengoi, first found in 1992) and the highly
invasive American comb jelly (Mnemiopsis leidyi,
first found in 2006). The further spread, biology
and feeding ecology (especially their potential
impacts on Baltic food webs) of these species
must be monitored carefully.
Every single species establishment in a novel
region and ecosystem opens new opportunities
for ecological research. These usually unintentional
‘transplantation experiments’ can be used for the
study of concepts such as adaptive strategies, niche
dimensions, interspecific relationships, and dispersal
mechanisms (Leppäkoski 2002).
Socio-economic impacts
The newcomers affect the ecosystem services
available for humans, such as primary production,
degradation capacity, fish production, recreational
uses and amenities.