Swimming behavior and mortality of the indigenous amphipod Monoporeia affinis in presence of the invasive polychaete Marenzelleria spp. in the Baltic Sea

Abstract

The Monoporeia affinis population has declined drastically in the Baltic Sea since 1999. In the late 1980’s, an invasive polychaete, Marenzelleria spp., established in the Baltic Sea. This experiment aimed to investigate if M. affinis’ swimming behavior and mortality was affected by competition from Marenzelleria spp., and if so the competition was size- or densitydependent. One control series without Marenzelleria spp. and four series with different sizes and densities of Marenzelleria spp. were studied during 20 days, to determine potential effects of Marenzelleria spp.  No statistically significant results were found neither for differences in swimming behavior between treatments, or in amphipod mortality between treatments. However, a statistically significant difference in swimming behavior over time within treatments was found in one treatment. The experiments did not show any negative impact on M. affinis from the presence of Marenzelleria spp