A welcome can of worms? Hypoxia mitigation by an invasive species
Invasive species and oxygen-depleted bottom waters are both considered significant threats to Baltic Sea ecosystems. Nevertheless, a recent study suggests that a non-native worm may actually help in the remediation of previously hypoxic regions.
Since the 1950s, low oxygen regions of the Baltic Sea have grown largely as a result of increased
nutrient-loading due to human activities, which has lead to a loss of habitat for animals that are
unable to tolerate hypoxic or sulphidic bottom waters. When conditions improve, the absence of
a native community leaves the system vulnerable to colonization by non-native species, which may
have the potential to change the system on a large scale.
At present, the Baltic Sea is home to 77 known established invasive species. One such example
is Marenzelleria spp., a non-native worm first observed in the Baltic Sea in 1985, which has become
one of the dominant benthic taxa in the northern Baltic Sea.
Invasive species affect sediment geochemistry
The rapid growth of Marenzelle
ria populations in the Stockholm archipelago coincided with lower than expected bottom water
phosphorus concentrations, prompting speculation that Marenzelleria was responsible for reducing
eutrophication in the region.
Daniel Reed (Baltic Nest Institute) and Joanna Norkko (Åbo Akademi University), together
with colleagues from the BONUS+ HYPER project, set out to discover whether the Marenzelleria
invasion could explain the observed improvement in water quality. Simulations with a reactive-
transport model revealed that colonization of sediments by dense Marenzelleria populations affects
sediment geochemistry in a complex manner, but ultimately increases the retention of phosphorus
in sediments.
Indeed, on a regional scale the change is large enough to alleviate eutrophication as
a result. Contrary to the negative connotations usually associated with invasive species, the study
showed that they have the potential to provide unexpected yet useful ecosystem services.
This work was published recently in Global Change Biology and will be featured as aResearch
Highlight in Nature Geoscience in October.
Full reference:
A welcome can of worms? Hypoxia mitigation by an invasive species, Global Change Biology (2011), Joanna Norkko, Daniel C. Reed, Karen Timmermann, Alf Norkko, Bo G. Gustafsson, Erik Bonsdorff, Caroline P. Slomp, Jacob Carstensen and Daniel J. Conley. DOI: 10.1111/j.1365-2486.2011.02513.x
