Recent massive invasions of the circumboreal sea anemone Metridium senile in North and South Patagonia

The circumboreal sea anemone species Metridium senile is a non-native species in Chilean Patagonia. The species is responsible for the occupation of large tracts of benthic substrate, threatening benthic resources such as sea urchins and barnacles. It has potentially devastating ecological impact on the overall benthic community. Species associated to the genus Metridium have been alluded to in the historical literature on Chilean marine life by various names. We summarize and evaluate their appearance in the literature and suggest eliminating the name Metridium senile lobatum for the South American subspecies. The first appearance of Metridium senile was confirmed in 2005 by the authors from Central Patagonia. Subsequently it was noted as abundant at multiple sites. In North Patagonia, it was first recorded from one site in 2011, followed by one more record in 2013 and several in 2015. In subsequent years, it has been recorded at an increasing number of sites based on our surveying. During our most recent surveys in 2021, we confirmed that it remains abundant at numerous sites throughout North Patagonia. In South Patagonia, it was first reported in 2015 from one site in the Straits of Magellan, and from two further sites around Cape Horn in 2017. It has not been recorded at additional sites nor has it significantly increased in abundance in southern Chilean Patagonia. However, it has been observed to be common at the Becasses Islands in the Argentinean part of Beagle Channel in 2021. Therefore, we recommend starting a monitoring program and putting restrictions on the transport of benthic invertebrates to avoid introducing the species to sites where it is not present yet.