Reef Restoration Foundation Hastings Reef Coral Nursery Monitoring: December 2019 - July 2020

This document outlines the methods, analysis and results that answer three key questions for the Reef Restoration Foundation: 1. Is there an impact of harvesting fragments on donor colonies? 2. Do nursery corals perform better than reef corals in the natural reef environment? 3. How do different species perform in the nursery? Data was collected in December 2019/ January 2020, April 2020 and July 2020 to answer these questions at Hastings Reef. For question 1, we found that harvesting fragments from donor colonies had no significant detrimental effects on those donors. Net and relative growth was not affected, colony mortality did not increase, and colonies were not more susceptible to adverse health outcomes in terms of bleaching, predation and disease. For question 2, we found there were significant linear growth advantages for corals within the nursery. Net linear growth after 6 months in the nursery was more than double the linear growth of reef corals. Importantly, nursery benefits in net linear growth were not realised at 3 months. Relative linear growth also was significantly greater in the nursery than on the reef. We also found that nursery corals appear less susceptible to predation and disease than reef corals, with none observed on any nursery corals. Nursery corals were, however, more susceptible to bleaching. Bleaching was almost 3 times greater in the nursery than for reef colonies. Mortality increased significantly over time for nursery corals but not reef corals. However, the variation around mortality estimates for reef corals was large due to the much smaller sample size than in the nursery. It should be noted that within each of the three sampling periods mortality did not differ significantly between nursery and reef corals. For question 3, we found that no one species was a stand out in terms of linear growth. A. muricata was the best performing species for net linear growth, adding significantly more linear growth to that species’ fragments, particularly compared to A. cerealis which had the smallest net linear growth. This result was likely in part due to different starting points in fragment size: A. muricata fragments were the largest when placed in the nursery and A. cerealis were the smallest. Because of this, relative linear growth is likely a better indicator metric when comparing species. In addition, A. muricata findings were somewhat expected; this species is known to have one of the fastest linear growth rates of all Acropora spp. in the Indo-Pacific (Jinendradasa and Ekaratne 2002). Relative linear growth indicated that after 3 months A. microphthalma lagged significantly behind all other species; however, after 6 months in the nursery this species had caught up and all four species had similar relative linear growth. There was significant bleaching in the nursery in April 2020, with 54% of fragments bleached. This was a significant increase from 25% bleaching in January. By July, no bleaching was recorded in the nursery. A. elseyi was the most resistant species to bleaching. Mortality of fragments increased significantly in the first 3 months in the nursery, from 3% at the time of attachment to 28% after 3 months. Mortality then plateaued between 3 and 6 months. No species was significantly more (or less) prone to mortality. No predation or disease was recorded on any nursery fragments