What drives the winter behaviour and ecology of the temperate coral Astrangia poculata? An examination of thermal and nutritional cues

In temperate ecosystems, accessing subtidal environments in the winter is challenging, and therefore, winter ecology and seasonal variation are understudied. For the temperate coral Astrangia poculata, winter is thought to be a period of biological ‘reset’, in which many cellular processes slow or stop, and the microbiome and symbiont community shift dramatically. The period of quiescence, when corals enter a dormant state with limited feeding or metabolic activity, is primarily driven by cold temperatures. However, other ecological drivers of quiescence remain unclear. Here, we documented quiescence in symbiotic and aposymbiotic colonies of A. poculata over a four-month winter period at two depths. First, we confirmed that quiescence is strongly associated with water temperatures under 6°C. Although we quantified a thermocline associated with depth, there was no influence of depth on quiescence. Symbiotic corals were more likely than aposymbiotic corals to enter quiescence, and higher chlorophyll α concentration was associated with lower quiescence, indicating a nutritional link to quiescence in A. poculata. Finally, we compared our results with previous quiescence observations and determined that the dormancy period is shorter in warmer winters, which has implications for the future ecology and behaviour of A. poculata in an era of global change.