Exploring substrate associations of the non-native anemone Diadumene lineata on an open ocean coast in the SW Atlantic

Diadumene lineata is one of the most widely distributed sea anemones in the world. It is usually found in estuaries, gulfs and bays over a broad range of substrates such as oysters, rocks, seaweeds and docks. In this study, we report the presence of D. lineata in a rocky outcrop located on an open ocean sandy beach on the Argentinian coast. We analysed the occurrence, abundance and size of anemones on two biogenic substrates: the native mussel Brachidonthes rodriguezii and the invasive oyster Magallana gigas. The probability of occurrence of the anemone was significantly higher in oysters compared to mussels, and since M. gigas is scattered and sparsely distributed among the mussels, we suggest that oysters may provide a more suitable substrate for the growth and reproduction of the anemone. Larger mussels and oysters supported a greater number of anemones, indicating a non-random distribution that favoured larger individuals within the patches. A marginally significant relationship was observed between the size of anemones and oysters, suggesting that larger oysters offer better growth conditions for this species. We propose that the presence of D. lineata on the open ocean sandy beach is associated with the previous record of M. gigas in the area, suggesting a potential invasional meltdown process between these exotic species.