A comparison of in situ and on-vessel larval rearing for coral seeding

Coral sexual recruitment is critical to reef recovery yet often fails on degraded reefs. Coral seeding is one approach to artificially increase the densities of coral settlers on reefs and can be applied in many ways. A thorough comparison of seeding-method performance is needed to inform restoration decisions yet is difficult to undertake given the cost and complexities around employing multiple methods simultaneously. Here, we first designed a vessel-based coral-spawning aquaculture system. Then we undertook an experimental comparison of the performance of larvae reared in the on-vessel system with those reared in in situ rearing pools (SECORE coral rearing in situ basins [CRIBs]). We parameterized survival estimates and assessed post-deployment survival of spat generated using each method. We also quantified survival of spat reared in situ and deployed across six sites on an inshore reef system of the Great Barrier Reef. Larval survival was lower when rearing in situ than on the vessel (3.8 vs. 66.1%, respectively), but settlement behavior and post-settlement survival were comparable between rearing treatments, with yield averaging 66 and 72% after 3 months of deployment, from CRIBs and culture tanks, respectively. Spat survival was also comparable across treatments, averaging 5 ± 8%. On-vessel rearing was more costly but supported higher survival, increased portability, and enabled more control and manipulation of rearing conditions. By contrast, in situ methods were low-cost, deployable from shore, and low-maintenance. Armed with this information, managers and practitioners can determine the most appropriate method(s) for a given restoration project.