Recolonization behavior of rapa whelk (Rapana venosa) and common starfish (Asterias rubens) eradicated from mussel bed

ABSTRACT This study aimed to investigate the recolonization behaviour of the rapa whelk (Rapana venosa) and the common starfish (Asterias rubens) on the mussel beds in their natural habitat. The monitoring studies were carried out seasonally on an island covered by a complete mussel bed in the Sea of Marmara (Turkey) between 19 October 2020 and 9 August 2021. Inhabitant rapa whelk and common starfish on the experimental study island (ESI) were tagged, then moved 10 m away from ESI. The recolonization potential of tagged invaders was monitored for 14 days with underwater surveys after their local eradication each season. The percentage of returned rapa whelk to the ESI was higher than common starfish end of the monitoring period. Rapa whelk moved non-stop towards the mussel bed, reaching the ESI at the latest 6th hour. Common starfish reached the mussel bed much later (at the 15th hour) than rapa whelk. The common starfish began to leave the ESI at the end of the 7th day, while the rapa whelk addicted to the ESI for 14 days. Re-invasion behaviour varied significantly seasonally, and both invaders reached the ESI much later in winter. During the monitoring periods, the highest invader densities were seen in the patches with the most abundant mussels, indicating continued uninterrupted feeding. The re-invasion duration and daily feeding activities support the spread of these invaders and could be considered a threat to marine resources.