Locality-based community science facilitates early detection and monitoring: the case of an extralimital population of a brachyuran crab

Practitioners of community science who are based at a locality and who are familiar with the local ecosystem can provide opportunities to supplement formal monitoring efforts.Between 2021 and 2023, we established a working relationship with a yearround resident recreational fisher who was engaged with monitoring as a community scientist.As a result, the first extralimital record of Portunus segnis (commonly known as the blue swimming crab) in temperate waters of South Africa was detected in January of 2020 in the Kowie River on the south coast.Following this discovery, two additional specimens were found in the estuarine reaches of the same river in December 2021.This report provides evidence of a population of P. segnis persisting outside its native tropical range and, in addition to morphological identification, species verification was confirmed using genetic barcoding.The circumstances of finding these specimens underscore the importance of establishing and maintaining relationships between local resource users and researchers to facilitate the identification and monitoring of introduced and range expanding species and to provide formal scientific documentation and rapid communication of species occurrences and persistence outside their native range.