ABSTRACT  

Global warming and heavy metals have become the major threat to the growth and reproduction of corals. However, unlike scleractinian corals, in the context of widespread coral degradation worldwide, there are few reports on the response of octocorallia corals to high-temperature stress and heavy metals. In the present study, we conducted indoor simulation experiments using Junceella squamata. We evaluated the physiological response of these corals under high-temperature stress at 33 ◦C and cadmium (Cd) stress by comparing the composition and diversity of their symbiotic bacteria and analyzing differences in their transcriptome. The results show that high-temperature stress has more severe adverse effects than cadmium stress. High-temperature stress disrupts coral symbiotic relationships, leading to an increase in alpha diversity associated with disease-causing bacteria, which may increase the risk of infection and potentially contribute to coral mortality. Meanwhile, cadmium stress increases the instability of the coral holobiont, potentially disrupting DNA stability and RNA transcriptional regulation. However, an increase in Cd-tolerant bacteria may help corals respond to cadmium stress. This study reveals the effects of harmful substances on coral and highlights the urgent need for action to protect octocorals in the face of environmental stress.