An aquarium experiment to measure impacts of non-native worms
Coastal ecosystems have highly valuable goods and services for human society and provide important ecological functions (such as primary and secondary productions and nutrient cycling).
Invertebrates living in those areas, such as worms, play an important role by linking organic material with predators, providing food to fish for instance. However, in the last decades, these areas have been experiencing increasing threats, mainly due to human activities. They are particularly vulnerable to species introductions. The Baltic Sea is a very special environment with its brackish water, young ecological age and low number of species. This contributes to nonnative species establishment.
The number of worm species is very small in the northern Baltic. Consequently, the introductions of two worms, Boccardiella ligerica and Marenzelleria spp., represent a substantial increase in polychaete diversity. Usually, species invasions are considered as a major threat to ecosystem functioning. However, given Boccardiella abundance in some brackish habitats, this species may play an important role in estuarine food webs, as a consumer of phytoplankton and detritus, and as food for small fishes and predatory invertebrates in low salinity regions. Regarding Marenzelleria worms, they have a different way to move in the sediment than the local species. They could then be potentially positive for the ecosystem by bringing new functions in the Baltic. In consequences, predators could also benefit from their presence.
The invasive worm Marenzelleria spp. is one of the most successful nonnative species in the Baltic Sea. First observed in the Baltic Sea in 1985, they quickly colonized the entire sea, occupying a dominant position in the communities.
The invasive worm Boccardiella ligerica was first found in southwestern Finland in 1963. They are small and live in a tube constructed of mucus and sediments.
Aims, questions, issues
Questions we want to adress:
How these worms impact other invertebrates (species and functions) in sediment?
Do those two different species of invasive worms have a different impact?
What are the consequences of these effects on predators?
How to answer those questions?
In order to answer our questions, we decided to set up an aquaria expriment at Husö Biological Station on Åland Islands (Finland).
24 aquaria have been set-up in order to measure and compare the differential impacts of two different non-native worm species (Marenzelleria spp. and Boccardiella ligerica) on invertebrate and bacterial communities. In order to understand implications for predators, we used sand gobies (Pomatoschistus minutus).