Non‐native species are a global issue for marine protected areas

The global extent of marine protected areas (MPAs) is increasing as nations strive to meet UN conservation targets, yet non‐native species (NNS) are a critically overlooked stressor that threatens MPA conservation goals. Despite evidence that marine NNS affect protected species and habitats, there is limited understanding of the pervasiveness of this threat and the extent to which resource managers are responding to it. We disseminated a questionnaire targeting MPA practitioners and scientists to determine the overall state of knowledge and perception of NNS in MPAs. We received 151 responses from individuals in 47 countries and territories, including a total of 116 MPAs of which 73 were reported to have NNS present. Although NNS are a prevalent issue in MPAs and are the subject of some monitoring, management, and research, preventative measures are largely absent, so that more focused attention on NNS will be required to achieve conservation goals. Marine protected areas (MPAs) reduce biodiversity ？？declines by mitigating anthropogenic impacts, including overfishing, habitat degradation, and, to some extent, climate change (Roberts et al. 2017). MPAs that prevent extractive activities increase fish biomass and diversity of large, predatory fishes (Edgar et al. 2014). There has been a substantial increase in MPAs (ranging from lightly to fully protected) following the international agreement to protect 10% of the ocean by 2020 (Aichi Target #11, Sustainable Development Goal #14) (Lubchenco and Grorud‐Colvert 2015). As of August 2019, MPAs cover 4.8% of the global ocean (www.mpaatlas.org). However, adequate human and financial resources to manage and mitigate anthropogenic impacts within MPAs are critical for protection to be effective (Gill et al. 2017). Non‐native species (NNS) are a major threat to marine biodiversity (Molnar et al. 2008), but are often overlooked as an anthropogenic stressor that may hinder the conservation efforts of MPAs. There are several documented cases of marine NNS deterring conservation goals. For instance, NNS have altered invertebrate community composition (Kaplan et al. 2018), outcompeted native species (Gallagher et al. 2017), and restructured benthic habitat (Coma et al. 2011) in MPAs in Canada, Ireland, and the Mediterranean, respectively. The Dutch–German–Danish Wadden Sea MPA contains 66 NNS, whose diverse presence, without considering impact, compromises the conservation goal of maintaining the ecosystem in its natural state (Buschbaum et al. 2012). The spread of NNS from unprotected areas into MPAs is highly