Do corals adapt their annual symbiotic metabolism strategies to cope with seasonal temperature stress and nitrogen pollution?

Abstract

Rising global sea temperatures and localized eutrophication threaten the integrity of the coral-algal symbioses in coastal reef communities. The propensity to adapt host-symbiont metabolic interactions during periods of warming may mediate negative effects to their overall physiology, such as bleaching. Coral species vary in their capacity for heterotrophy which, for corals, relies on passive suspension feeding. This study examines five coral species in Hong Kong (Acropora digitifera, Montipora peltiformis, Galaxea fascicularis, Oulastrea crispata, and Porites lobata) and explores changes in their metabolic strategies from autotrophy to heterotrophy, and vice versa, in accordance with seasonal temperature extremes as an adaptation to cope with unprecedented nitrogen pollution. We monitored host lipid content, in hospite Symbiodinium photochemistry using PAM flourometry, and photosynthesis/respiration (P/R) of the holobiont every month from August 2015 until the present. We have found that during colder, winter months (December/January) A. digitifera and G. fascicularis exhibited higher P/R ratios and greater photochemical efficiency, whereas P. lobata showed no change. These data indicate that some species are adapting their metabolic strategies according to seasonal temperature changes. This adaptation may offset the burden Symbiodinium imposes under conditions of high, localized nitrogen pollution during warmer, summer months (July/August/September).