نبذة مختصرة : The Northern Star Coral (Astrangia poculata) is an understudied temperate scleractinian coral that provides unique opportunities to understand the roles of phenotypic plasticity and local adaptation in coral physiological tolerance limits. Astrangia poculata inhabits hard bottom ecosystems from the northwestern Atlantic to the Gulf of Mexico and withstands an annual temperature range up to 20°C. Additionally, A. poculata is facultatively symbiotic and co-occurs in both symbiotic (“brown”) and aposymbiotic (“white”) states. Here, brown and white A. poculata were collected from Virginia (VA) and Rhode Island (RI), USA and exposed to heat (18-32°C) and cold (18-6°C) temperature assays during which photosynthesis (P), respiration (R), and symbiont photochemical efficiency (Fv/Fm) were measured. Thermal performance curves (TPCs) of respiration revealed differences consistent with local adaptation of the RI and VA populations to their natal thermal environments. RI corals exhibited higher respiration rates overall, and higher respiration at 6, 15, 18, 22, and 26°C. Additionally, thermal optimum (Topt) analyses show a 3.76°C (brown) and 6.88°C (white) greater Topt in the VA population, corresponding to the warmer in situ thermal environment in VA. In contrast to respiration, no origin effect was detected in photosynthesis rates or Fv/Fm, suggesting a possible host-only signature of local adaptation. This study is the first to consider A. poculata’s response to both heat and cold stress across symbiotic states and geography and provides insight into the effects of future climate change on valuable hard bottom communities along the East Coast of the US.
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