Integrating grazing and food supplementation in coral restoration to enhance settler survival and growth

Sexual coral propagation faces a significant bottleneck due to high post-settlement mortality, impeding large-scale reef restoration. This study assessed the effectiveness of co-culturing Diploria labyrinthiformis settlers with the herbivorous gastropod Cerithium lutosum and supplementing their diet with a commercially available food source, Reef-Roids, to enhance settler survival and growth. Settlers were reared for 10 weeks under controlled conditions in one of four treatments: Control (C), Feeding with Reef-Roids (F), Grazing by C. lutosum (G), and combined Feeding + Grazing (FG). Settlers in the Grazing treatment exhibited the highest survival at 87% after 10 weeks, significantly outperforming those in the Control (43%) and Feeding (48%) treatments. The combined feeding and grazing treatment improved survival rates to 74% and resulted in the highest growth rates, with settlers in this group averaging 11.98 ± 2.38 mm², approximately 3.4-fold larger than the control and 2.6-fold larger than the feeding group. The feeding treatment alone did not significantly enhance survival or growth, underscoring the critical role of grazing in mitigating algal competition and promoting settler development. The results highlight the efficacy of grazing by C. lutosum (G and FG) in improving both survival and growth of coral settlers, substantially surpassing the outcomes of ungrazed treatments (F and C). This study highlights the potential of integrating microherbivores, such as C. lutosum, in ex situ coral nurseries. By regulating algal growth, these grazers minimize the need for labor-intensive maintenance, offering a scalable and cost-effective strategy to mitigate the high mortality rates of coral settlers.