Title: A within-site comparison of intertidal and subtidal populations of Astrangia poculata

Abstract: Astrangia poculata (Northern-star coral) exists in both the intertidal and subtidal habitats in southern New England. As such, they inhabit exceptionally dynamic environments. Though subtidal populations have been well studied, few studies exist examining basic physiological parameters between adjacent intertidal and subtidal populations. The objective of this study was to compare factors controlling intertidal coral resilience that allow them to withstand extreme environmental fluctuations. Corals were collected from the intertidal and subtidal zones at Fort Wetherill, Rhode Island, then acclimated to lab conditions at Southern Connecticut State University. We exposed intertidal and subtidal colonies to thermal challenges of either heat or cold stress (5°C, 15°C, 18°C, 22°C, and 27°C) based on historical averages in the region. To assess physiological differences between intertidal and subtidal populations, we measured feeding responses, fluorescent yield, and dissolved oxygen (DO) concentration both before and after exposure to thermal challenge. Temperature had a significant impact on feeding responses, with a collapse of all feeding behavior in the 5°C treatment after all corals in this group entered a winter dormancy period called quiescence. We observed an inverse relationship between temperature treatment and DO concentration, with higher DO produced by corals in cold temperature treatments and low levels of DO, or DO consumption, in the warm temperature treatments. Intertidal or subtidal collection site significantly impacted fluorescent yield, with intertidal corals exhibiting higher and more variable fluorescence than subtidal corals. All corals in the 5°C treatment entered quiescence, regardless of collection site, allowing for measurements on quiescent A. poculata to be taken for the first time in a laboratory setting. The results of this study have important implications for the fields of temperate coral resilience, intertidal coral communities, and cnidarian dormancy.