Tracking the coastal bioinvasion by mussels in Hong Kong

Invasive species are key drivers of global biodiversity decline and threats to marine conservation. Hong Kong, being a trade and transport hub with large volumes of shipping traffic, is particularly susceptible to marine bioinvasions and the subsequent ecological and economic consequences. While invasive bivalves have been recorded in Hong Kong, notably the mussel Xenostrobus securis, their distribution and population characteristics have not been recently documented. Here, we used field surveys to update occurrence records of this mussel and found it persists at sites in Tolo Harbour where it was previously recorded, and also occurs at multiple sites within Tolo Harbour where it was previously absent, and in Victoria Harbour where previous records did not exist. Population characteristics of X. securis were similar to those quantified at survey sites where it was recorded previously, indicating the species has reached a relatively stable equilibrium. We also found that the similar native species, Brachidontes spp., had increased in abundance, and the abundance of another significant invader, Mytilopsis sallei, had reduced. Notably, we documented the occurrence of another invasive bivalve, Mytella strigata, which was previously unreported in Hong Kong, highlighting the persistent risk of the arrival of novel species. With the increasingly widespread documentation of X. securis and record of yet another invasive species within the region, we suggest more research is required for monitoring and management of these species, and efforts should be made to quantify their ecological and economic effects.