Epsilon Open Archive

Abstract

Invasive species are spreading across the globe, putting pressure on habitats, biodiversity, and key ecosystem processes underpinning ecosystem services. The development of reliable and cost-effective management strategies for these species depends on on-going assessment to justify choices and mitigation initiatives. The invasive macrophyte, Elodea canadensis Michx., is one such invasive species spreading deeper into the boreal region of Scandinavia. I aimed to identify a set of traits that contribute to the success of E. canadensis in Swedish boreal lakes and investigate impacts on biodiversity (macrophyte and macroinvertebrates assemblages) and ecosystem functions (biofilm metabolism, leaf litter decomposition and nutrient uptake). I achieved this through field studies in six boreal lakes (three invaded by E. canadensis), together with a mesocosm experiment. In the experiment, I varied macrophyte diversity and the relative abundance of two invasive macrophytes and quantified macrophyte productivity and nutrient uptake after a drought treatment. In the field, I found that E. canadensis started regrowing earlier in the spring than native species. The invasive macrophyte also grew faster as density of its conspecifics increased. Diversity composition of both macrophytes and macroinvertebrates inhabiting the macrophytes differed between invaded and uninvaded lakes. Multiple aspects of ecosystem functioning differed between invaded and uninvaded lakes. The biomass accrual, gross primary productivity of respiration of biofilms, and rates of leaf decomposition were all elevated in invaded lakes, as was entrapment of particulate organic matter. Biofilms were overall nitrogen limited, but nutrient limitation was lower in the invaded than uninvaded lakes. In the mesocosm experiment I found that positive effects of macrophyte diversity on productivity and nutrient uptake decreased as the number of invasive species increased, with only limited evidence that the invasive species altered the impacts of drought.

Although E. canadensis is a well-established invasive species, it still impacts biodiversity and functioning in boreal lake ecosystems. In combination with its potential to spread further north, highlights the need to prioritise this and other similar species in management.