Rayed pearl oyster Pinctada radiata (Leach, 1814) (Bivalvia: Pteriidae) in the eastern Adriatic Sea – recent observations

Abstract

Adriatic Sea as a part of the Mediterranean is settled by many introduced species which extend their range northward. Among them is the rayed pearl oyster Pinctada radiata, a mollusk of Indo-Pacific origin that colonises habitats throughout the Mediterranean. P. radiata established a population in a fish farm on the island of Mljet in the Adriatic Sea, which was observed in 2017. To determine the status of the population, 48 specimens of P. radiata were randomly sampled from the ropes of a fish farm in 2019. Morphometric parameters were determined using a digital calliper. The recorded parameters showed that shell height ranged from 50.55 mm to 72.98 mm, shell length from 46.66 mm to 71.15 mm, and shell width from 19.98 mm to 58.54 mm. During additional visual survey in 2020 the presence of the spat within population at Mljet fish farm was not observed. It appears that only adult specimens are present, and it is unclear if the population is reproducing. In addition, P. radiata spat was observed in the shallow waters of Lokrum Island in 2021 and 2022, indicating the possibility of survival of larvae naturally dispersing from pre-existing populations. An adult specimen of P. radiata was also observed in Mali Ston Bay on two occasions, in 2009 and 2021. P. radiata, a highly adaptable species that tolerates a wide range of environmental factors, has successfully colonised new habitats.