Community dynamics and physiology of Symbiodinium spp. before, during, and after a coral bleaching event

Community dynamics and physiology of Symbiodinium associated with Orbicella (= Montastraea) faveolata were examined before, during, and after a thermally induced coral bleaching event in Puerto Morelos, Mexico. We combined microsampling molecular genotyping with in situ pulse-amplitude modulated fluorometry to correlate colony variability of Symbiodinium population identities and the phenomena of partial coral bleaching. Pigmented nonbleached portions of O. (= M.) faveolata were compared with bleached portions of the same colony. During bleaching, maximum quantum yield of photosystem II (PSII; F_v: F_m) was significantly lower and highly variable (range 0.110 to 0.680) compared with previous summers in which coral bleaching was absent (range 0.516 to 0.661) and recovery (range 0.480 to 0.716). Differential susceptibility to environmental perturbation of F_v: F_m corresponded to distinct genetic identities of Symbiodinium. Analysis of ribosomal deoxyribonucleic acid (rDNA) internal transcribed spacer 2 (ITS2) revealed regions of the coral colonies that had phylotype A3 prior to bleaching were more resistant to the bleaching perturbation than adjacent bleaching-prone patches that harbored phylotypes B17 and C7. During environmental perturbation, regions of the colonies containing predominantly Symbiodinium phylotypes A3 or D1a retained significantly higher F_v: F_m values than adjacent regions with phylotypes B17 and C7. Following bleaching, rapid recovery of symbiotic algal densities greatly exceeded normal seasonal oscillations. During recovery we document shifts in Symbiodinium populations and increase prevalence of Symbiodinium types A3 and D1a, phylotypes known to have enhanced thermal tolerances. Thermal tolerance of Symbiodinium spp. influences the changes of coral-Symbiodinium communities during disturbance events and the dynamics of coral-Symbiodinium repopulation.