Economic effects of the invasive worm Marenzelleria spp. in the Baltic Sea

Impacts of alien marine species on ecosystem services have been documented in numerous studies, but studies on the estimation of costs with an explicit quantification of the impact channels are lacking. We calculated costs of the invasive worm Marenzelleria in the Baltic Sea, which affects sea bottoms capacity to store nutrients. A reduced capacity implies higher costs for reaching nutrient reduction targets. Therefore, the costs were calculated by taking the difference in minimum costs of attaining nutrient targets with and without the presence of the invasive species. To this end, we developed a simple dynamic model which captures the effect of the invasive species on the decay rates of nutrient pools in different and interconnected sea basins in the Baltic Sea. Evidence and numerical estimates were found for a decrease in sequestration of phosphorus in the different sea basins caused by the occurrence of the invasive worm. The results indicated a cost of this effect that ranges between 167 billion SEK and 732 billion SEK depending on the effect of Marenzelleria on sequestration of phosphorus. This cost corresponds to 0.02-0.08% of total gross domestic product of the nine coastal countries. However, the cost is unevenly distributed among the countries, where Poland bears the largest part because of its large phosphorus loads and access to low cost options.