Improved coral nursery production through contingent heat stress events via depth manipulation

Abstract

Ocean-based coral aquaculture is increasingly employed to generate biomass for active coral reef restoration. As this practice expands in scale and global application, it is important to explore techniques that optimize nursery yield amid climate change and dynamic environmental conditions. Therefore, we constructed three suspended coral nurseries in Malaysia to test whether increasing coral nursery depth protects biomass production from detrimental heat stress impacts while assessing potential trade-offs in growth and survival. The study focused on three coral species: Acropora muricata, Acropora cf. gemmifera, and Montipora aequituberculata. One nursery was maintained at the original source material collection depth of 8.0 m (Shallow), another was lowered to a depth of 15 m (Deep), and the third nursery (Transitional) was gradually transitioned from 8 to 15 m over a 71 day period. Coral growth and survival were monitored for 582 days, representing the longest observational nursery study yet reported in Malaysia. In addition, these data capture the impacts of the first back-to-back coral bleaching events recorded in the region, as well as a period of heavy tropical storm activity (i.e., northeast monsoon season). Ultimately, major findings include (1) species-specific differences in growth and survival across nurseries, (2) A. muricata exhibited the highest growth rates (0.28 ± 0.02 % day⁻¹) in the Shallow nursery, while M. aequituberculata had the lowest (0.16 ± 0.02 % day⁻¹) in the Deep nursery, (3) survival was the highest at 15 m, with A. gemmifera displaying the greatest survival rate (88 %), and (4) significantly lower heat stress response and bleaching in corals cultured in deeper nurseries. These results suggest that depth manipulation could be a viable strategy for mitigating heat stress impacts in coral nurseries while maintaining favorable biomass production. This study provides key insights for optimizing coral restoration efforts in the Indo-Pacific, where climate change increasingly threatens coral reefs.