Abstract Summary
Recent back-to-back episodes of heat-induced coral bleaching in Florida and elsewhere have driven the need to test interventions that increase the resilience of restored corals to anticipated future warming. One potential intervention is the application of sublethal doses of bleaching stress to induce compensatory responses in reef corals during recovery that would increase their resistance to subsequent thermal stress (“stress hardening”). We trialed different methods for stress-hardening corals as part of a restoration program in Miami, FL, and used quantitative PCR (qPCR) and chlorophyll fluorometry (I-PAM) to assess changes in the structure and function of algal symbiont communities (Symbiodinium spp.). We tested the effect of high irradiance and the herbicide Diuron (DCMU: 3-(3,4-dichlorophenyl)-1,1-dimethylurea) on the bleaching and recovery of 8 genotypes of the threatened Caribbean staghorn coral Acropora cervicornis. For high light stress, we exposed corals to ~2,000 umol photons/m2/s PAR, which decreased photochemical efficiency (Fv/Fm) and resulted in visible bleaching within 3 weeks. These corals were then allowed to recover in the field and further changes monitored using qPCR. We also tested the effect of short-term exposure (1h, 2h and 6h) to three concentrations of DCMU (0.45mg/L, 4.5mg/L and 41.85mg/L) on coral bleaching and recovery. All concentrations resulted in rapid (< 1 h) decreases in Fv/Fm in A. cervicornis, but these values returned to normal after one day of recovery, suggesting longer exposure times are needed to induce symbiont expulsion. We will report on continued trials using longer DCMU exposure times and the use of subsurface rafts to expose corals to high light in the field. Continued efforts are needed to quickly test the efficacy of low-technology methods of stress hardening corals that can be scaled and incorporated into restoration efforts.
