Evidence of corallivorous gastropod Drupella cornus breeding on the higher latitude reefs of Rottnest Island (32°S), Western Australia

With increasing sea water temperatures, higher latitude temperate and sub-tropical coral reefs are becoming increasingly tropicalised. Although these cooler areas might offer refuge to tropical species escaping the heat, the reshaping of ecosystems can have devastating effects on the biodiversity in these areas, especially when habitat structure is affected. Recently, feeding aggregations of corallivorous gastropod Drupella cornus, a tropical species capable of large-scale reef degradation, were found at Rottnest Island in Western Australia (32°S). We provide evidence that D. cornus spawned at Rottnest Island for 2 consecutive years in 2021 and 2022, and Drupella veligers from an egg case collected at the island hatched and grew at temperatures in the laboratory that were predominantly lower than those at Rottnest Island at the same time. The spawning was possibly triggered by higher than usual La Niña-associated SSTs during the survey period, or the long period of high sea water temperature anomalies recorded around Rottnest Island. A spawning population of D. cornus can greatly affect these higher latitude reef areas, especially when accompanied by increased heat stress. Monitoring and management should be implemented to further understand what effects a breeding population of D. cornus has on Rottnest Island.