Alien Species Threaten the Delicate Baltic Sea

Alien or introduced species are species that have moved from one marine ecosystem to another through human activity. Since the early 1800s, about 120 alien species have entered the Baltic Sea, around 70 of which have remained there permanently. The number of new introduced species is rising all the time due to increased marine traffic. Alien species can cause dramatic changes in the Baltic Sea ecosystems by edging out native species.

Where do the introduced species come from?

Most of the introduced species come to the Baltic Sea in ballast waters or attached to ship hulls. Some of the species have also been used as fish food and some have even been planted for fishing purposes. Some crustaceans origin from artificial water reservoirs and certain alien species have also accidentally spread from aquariums, fish markets or research laboratories.

Alien species of the Baltic Sea come primarily from the North America and the Caspian and Black Sea regions. It’s been estimated that up to 4000 different species travel daily around the world in ships! Increased marine traffic, bigger cargos and quicker ships mean shorter travelling times also for the alien species making it easier for them to stay alive. Also the climate change eases up the adaptation process of some of the species.

Why do these species spread out so easily?

• Baltic Sea is a very sensitive ecosystem. Species of both high and low salinities live in the brackish water and face their physiological limits all the time making them highly vulnerable to changes of any kind.
• Baltic Sea isn’t particularly rich in species. There’s plenty of room and nourishment for alien species and little competition. Alien species don’t usually have any natural enemies in the new environment, so it’s easy for them to breed and spread out quickly.
• Some introduced species can change their way of reproduction according to the conditions. These species reproduce asexually in good conditions, and as the conditions get poorer, e.g. in the wintertime, they can form long-lasting dormant eggs as their breeding product. For instance Fishhook waterflea (Cercopagis pengoi) produces dormant eggs that sink to the sea bed and hatch out after the winter.

What kind of alien species are there in the Baltic Sea?

Bay barnacle Photo: Ilppo Vuorinen

There are different kinds of alien species; fishes, fish parasites, invertebrates and toxic algal species. The most well-known and harmful alien species are:

• Bay barnacle (Balanus improvisus)
• Fishhook waterflea (Cercopagis pengoi)
• Red-gilled mud worm (Marenzelleria viridis)
  
• Conrad’s false mussel (Mytilopsis leucophaeta).

Two species that are a threat and must be researched more thoroughly are:

• Round goby (Neogobius melanostomus)
• Zebra mussel (Dreissena polymorpha).

Some of the alien species are already a part of the ecosystem and can no longer be considered as strangers. A good example of an already established species is the bay barnacle that arrived to the Baltic Sea as early as the 1840s. Read more about the most common introduced species here.

What can be done to prevent future problems?

It’s impossible to try to wipe out all alien species or even to completely prevent their spreading. That’s why it’s essential to pay attention to ballast waters and develop technical innovations in shipping to prevent introduced species’ access to the Baltic Sea. A good way is to control ballast water intake: ballast waters shouldn’t be taken from the middle of an algal blooming or too near the sea bed.

When it comes to technical solutions to destroy the alien species, different methods have been developed. These include heating, filtration and ozone-, ultraviolet- or ultrasound processing. Lowering of pH value as well as chemicals or electric pulses can destroy the unwanted species.

But are the inrroduced species a threat or a part of normal life cycle? These species influence the power structure of native species. They set whole trophic webs in danger and potentially cause economic losses. On the other hand, some alien species are a new food source for the native fish. All in all, more research and new control methods are needed to protect delicate ecosystems like the Baltic Sea.

IMO’s Ballast Water Convention

International Maritime Organization (IMO) has prepared a convention on ballast water handling in 2004. The contract becomes valid step by step, when at least 30 countries ratify it. Read more about the convention at IMO's webpage .