Evaluating the impact of an increase in sea water temperature on the palmerolides of the Antarctic benthic tunicate Synoicum adareanum

: Global change is producing significant ecological impacts in Antarctic marine organisms, although most of them are still understudied. Here, we report the changes in the chemical profile of the colonial tunicate Synoicum adareanum in response to gradual temperature increases in controlled aquarium experiments as a proxy to determine the effects of global warming. This is the first study on the effects of increasing seawater temperature on the natural products of an Antarctic tunicate. From specimens collected at Livingston Island in the South Shetland Islands in January 2022, we isolated the known palmerolides A, B, D, F, and H (1-5). Palmerolides are a family of macrolides which are considered to play a defensive role against natural predators and exhibit also very potent pharmacological bioactivities. Our metabolomic study based on UPLC-HRESI-MS analysis demonstrated the impact of increasing temperatures on the natural products of S. adareanum, with a significant and massive increment of the amounts of all palmerolides as well as the onset of tunic necrosis at 4-5 °C. Further understanding these mechanisms at the molecular level in Antarctic marine benthic organisms may offer insights into how these ecosystems may respond to global change.