Two new alien crustacean invaders Grandidierella japonica (Stephensen, 1938) and Neomysis americana (SI Smith, 1873) in Belgium

The Japanese aorid amphipod Grandidierella japonica (Stephensen, 1938) and the North American opossum shrimp Neomysis americana (S.I. Smith, 1873) are reported here for the first time in Belgium. Both G. japonica and N. americana were found in hyperbenthic samples taken from just above the sediment surface during long-term monitoring of the Schelde estuary. Grandidierella japonica was detected for the first time in 2018 and has since appeared regularly in low numbers. Neomysis americana has probably been overlooked for some time and was found in high numbers (n = 155/40 m3) for the first time in July 2012. Since N. americana has been found with regular occurrence and in fairly high numbers (n = 0-3530/40 m3), a well-established population is assumed. The arrival of N. americana probably went unnoticed for some time due to confusion with the native species Neomysis integer.