staghorn coral

Bachelor thesis research project

The previously dominant, reef-building Acropora cervicornis abundance decreased drastically across the greater Caribbean area since the 1970s. This is mainly due to the white band disease (WBD) and coral bleaching events. They have been considered a critically endangered species by the IUCN Red List since 2008 and restoration efforts are paramount to assist recovery of this species population. The exceptionally high growth rate and possibility of fragmenting this species, make it very suitable for coral gardening. This technique grows coral colonies from small fragments in ex- or in-situ coral nurseries before out-planting them into the natural reef. To test which locations are best suited for focusing future out-planting efforts, all previous out-planting trials have been analyzed to select three promising locations. In this research, two rebar frames have been installed at each of these locations. Per location, one frame was equipped with 20 fragments of the genotype ‘HiC’ and the other one with 20 fragments of the genotype ‘LL’. For the following 70 days fragment health, survival, growth rates, sediment settlement, and turbidity have been measured biweekly. The growth rates at location ‘Nursery’ and ‘Big Rock Market’ did not differ, however, at location ‘Hole in the Corner’ the genotype HiC had a significantly higher growth rate compared to the other locations and genotypes. The high amount and variation of turbidity and sedimentation at the Nursery make this location unsuitable for out-planting efforts. Sedimentation at Big Rock Market was exceptionally low and consistent, which could benefit out-planting efforts, but faster growth rates at Hole in the Corner will yield more coral. Because the locations are approximately 1.5km apart and both are considered suitable, it is recommended to outplant at and in between both locations instead of focusing out-planting efforts on one location, in order to increase the resilience of the out-planting efforts against natural stressors such as new outbreaks of the WBD.

Abstract Coral reefs are some of the most diverse and valuable ecosystems worldwide. Since the 1970’s the coral populations of Acropora spp. around Bonaire Island have been declining due to White Band Disease (WBD) and due to heavy storms and hurricanes (i.e., hurricane Lenny in 1999). Acropora cervicornis is one of the species selected as restoration target because its critically endangered status according to the IUCN red list and its ecological value as reef builder. Promoting genetic diversity is key to aid the recovery of degraded populations and give this species higher chance to survive in the long-term. In this study, we measure growth and healing, as phenotypic traits of propagated corals to assess the different genotype performance in the nursery phase. Linear length and tissue regeneration have been monitored for 8 weeks for 10 different genotypes (n=5), respectively with in situ measurement and image analysis. The preliminary results suggest that some individual fragments can grow up to one centimeter per week and achieve complete tissue regeneration from cutting and handling damage in 15 days. Being able to determinate the differences in performance from various coral genotypes can help nursery based coral restoration to be more performant. Indeed, selecting coral genotypes that can grow and regenerate faster is a considerable advantage for coral restoration practitioners that could therefore optimize their outplanting efforts.