This study examined the physiological responses and trophic transfer of paralytic shellfish toxins (PSTs) from the mussel Perumytilus purpuratus to the carnivorous gastropod concholepas under different temperature scenarios simulating present (14 °C) and projected warming conditions (18 °C). Controlled mesocosm experiments were conducted using two diets containing varying concentrations of Alexandrium catenella cells to simulate low- and high-intensity harmful algal blooms (HABs). The results indicate that there was no significant effect of diet or temperature on the physiological response of C. concholepas, despite the high levels of toxins determined in its tissues as a result of constant exposure to prey with PSTs. Feeding rates and absorption efficiency of C. concholepas showed evidence of acclimation to chronic exposure, while metabolic indicators such as oxygen consumption increased under toxin exposure and elevated temperatures. Toxin profiles indicated active biotransformation, including desulfonation and desulfation processes, producing more toxic analogues such as saxitoxin (STX) and neosaxitoxin (NEO). Both P. purpuratus and C. concholepas exhibited high tolerance to PST accumulation, with toxin levels exceeding regulatory limits, particularly under warming conditions. These findings underscore the potential ecological and food safety risks associated with the combined effects of HABs and ocean warming in southern Chile, where A. catenella blooms are becoming increasingly frequent and intense.