There are a range of ecological interactions such as predator-prey and competitive interactions occurring constantly in all systems throughout the world. These interactions can have profound ecological effects on communities, influencing their structure and diversity. In addition, these interactions can have significant implications for species restoration efforts and management decisions. The abalone Haliotis iris is a culturally important species which has been the focus of targeted restoration efforts within the East Otago Taiāpure for 15 years. Despite these restoration efforts, H. iris densities at many reefs in the Taiāpure continue to decline. The present study attempts to highlight the importance of the predator-prey and competitive interactions occurring between Haliotis iris, Astrostole scabra (seven-armed sea star), and Cookia sulcata (Cook’s turban), in hopes of understanding if their interactions have the potential to threaten the recovery of depleted H. iris populations and affect restoration efforts within the Taiāpure. Field surveys of H. iris, C. sulcata, and A. scabra populations in the East Otago Taiāpure were completed at three paired sites, repeating a survey that had been completed in 2012. Using a series of experiments H. iris and C. sulcata feed selectivity in which bladder kelp (Macrocystis pyrifera), Asian seaweed/Wakame (Undaria pinnatifida), southern bull kelp (Durvillaea antarctica), sea lettuce (Ulva lactuca), and Flapjack seaweed (Carpophyllum flexuosum) were offered was examined, and grazing rates were investigated. Astrostole scabra prey preference and indirect consumptive effects were also assessed.

Field surveys identified decreases in H. iris density across all sites when compared to data from comparable surveys completed in 2012. On average across all sites, density has decreased from approximately four individuals per m2 in 2012 to 1.5 individuals per m2 in 2023. The areas where the majority of H. iris were found were also where the largest number of A. scabra were found, however, A. scabra density was not correlated with H. iris density. Site was found to be a significant factor influencing A. scabra density. Cookia sulcata densities showed decreases of animals at two of the six surveyed sites in 2023 compared with 2012. H. iris and C. sulcata significantly consumed the largest amounts of D. antarctica compared to the other four species and there were no significant differences in grazing rates between the two species. Haliotis iris grazing was found to be significantly higher when a predator chemical cue was present, whereas C. sulcata consumed similar amounts across both experiments. In the A. scabra prey preference experiments, H. iris was selected for the most by A. scabra, followed by C. sulcata. In conclusion, a further increase in A. scabra abundance and density may seriously threaten the restoration efforts and recovery of important H. iris populations. Continued monitoring of the abundance of both A. scabra and H. iris populations is crucial, and if A. scabra populations continue to increase their removal from restoration sites may be required. Cookia sulcata appear to be a generalist intertidal grazer and do not compete with H. iris for food, even though they prefer similar species. Cookia sulcata is also a preferred prey item for A. scabra, but when given the choice, will select H. iris more often.