Subtropical thermal variation supports persistence of corals but limits productivity of coral reefs

Concomitant to the decline of tropical corals caused by increasing global sea temperatures is the potential removal of barriers to species range expansions into subtropical and temperate habitats. In these habitats, species must tolerate lower annual mean temperature, wider annual temperature ranges, and lower minimum temperatures. To understand ecophysiological traits that will impact geographic range boundaries we monitored populations of five coral species within a marginal habitat and used a year of in situ measures to model thermal performance of vital host, symbiont, and holobiont physiology. Metabolic responses to temperature revealed two acclimatization strategies: peak productivity occurring at annual midpoint temperatures (4-6ºC lower than tropical counterparts), or at annual maxima. Modeled relationships between temperature and P:R were compared to a year of daily sub-tropical sea temperatures and revealed that the relatively short time spent at any one temperature, limited ...