To test whether food consumption in Haliotis squamata is a function of temperature (Experiment 1), we produced agar-pellets containing Ulva lactuca powder (Xi'an XiaoCao Botanical Development Co., Ltd, China). For the assays, in which we tested whether the diet composition of H. squamata changes with temperature (Experiment 2), fragments of living macroalgae from the Bay of Tidung Island, Thousand Islands, Indonesia, were used. We collected specimens of the red macroalga Gracilaria salicornia and algae belonging to several species of the Amphiroa (Rhodophyta) and Sargassum (Phaeophyceae), respectively, on 22 July 2018. In Experiment 1, food consumption rates of H. squamata were measured after the abalone had been acclimated to five temperatures levels, ranging from 27–33°C at 1.5°C intervals to identify the appropriate temperature range for Experiment 2. After a laboratory acclimation period of 7 d, during which the abalone were kept at 27°C, H. squamata specimens were transferred individually to plastic containers (1.5 L) to allow acclimation to the target temperatures. Each plastic container served as an experimental unit and was placed in one of five water baths. After all abalone had spent 3 d at 27°C, we started to increase the water temperature by 1°C per day (0.5°C in the morning and 0.5°C in the evening). To ensure that all target temperatures were reached on the same day, temperature rise in the different water baths was initiated successively. After all targeted temperatures were reached, we kept the abalone at these temperatures for another 3 d and then we conducted the feeding assays, which lasted for 24 h. In Experiment 2, thallus fragments from the three different algae were offered simultaneously. Furthermore, we ran the feeding assays with acclimated herbivores (AH) and non-acclimated algae (NA) as well as with non-acclimated (NH) herbivores and acclimated algae (AA). As in Experiment 1, H. squamata individuals were acclimated individually in plastic containers within different water baths, whereas macroalgae were kept together in larger aquaria (105 L and 201 L). Hence, Experiment 2 consisted of five experimental groups. In the first, the herbivore nor the algae were acclimated to elevated temperatures, but were kept at 27 °C. The two experimental scenarios (i.e. AH + NA and NH + AA) were both realized at two temperature levels and these combinations of experimental scenario and temperature constituted the four remaining experimental groups (Fig. 1). The feeding assays again lasted for 24 h and were conducted on 9 August 2018. We provided thallus tips to herbivores, which were similar to each other with regard to their surface area.
