Ocean warming and multiple source populations increase the threat of an invasive bryozoan to kelp beds in the northwest Atlantic Ocean

Abstract

Climate change is expected to create more favourable climatic conditions for many invasive species, increasing their abundance and range. One such invasive species is Membranipora membranacea, an epiphytic bryozoan causing defoliation of kelp beds in the northwest Atlantic Ocean (NWA). The impact of M. membranacea is directly linked to its abundance, which is anticipated to increase due to climate change. Additionally, further range expansion may threaten Arctic kelp beds in the future. We constructed a species distribution model (SDM) to predict the abundance of M. membranacea in the NWA under present and future climate scenarios. We also assessed the effect of a possible additional invasion of M. membranacea from populations in Norway. The projected future abundance distribution of M. membranacea in the NWA differed substantially depending on the future climate scenario employed, but the bryozoan was predicted to occur in the Arctic at low abundances regardless of the scenario. However, we also found that populations of M. membranacea in Norway achieve much higher abundances at lower temperatures than NWA populations and could pose a dire threat to kelp beds in the NWA and southern Canadian Arctic if introduced in these regions. Although the SDMs performed well under internal validation, estimating the impact of M. membranacea is complicated by the context-dependent response of kelp communities to coverage by the bryozoan. Nonetheless, this study provides valuable predictions of the response of an ecologically significant invasive species to climate change with findings of broader relevance to the study of other invasive organisms.