While biogeographical limits of tropical fauna have been studied with increasing latitude, little is known about their lower depth distributions. For non - photosynthetic, warm - water fauna, decreasing temperature with increasing depth eventually limits their depth distribution. However, the nature of this lower thermal threshold, which has habitat management implications, has not been studied to date. In the Au’au Channel, Hawai’i, the temperature regime along a depth gradient near previously identified lower depths limits for warm - water azooxanthellate corals was characterized to determine whether the lower depths limits were consistent with acute stress causing colony mortality or chronic stress inhibiting growth, rep roduction, and/or larval settlement. Data suggests that lower depth limits are associated with a minimum required exposure (e.g., 5 - 7 months) to water >22°C. This lower depth limit appears to be decoupled from the lower temperature limits of colony survival.