Improving and expanding the portfolio of grazers available for coral co-culture and reef restoration – Phase II

This report contains information on activities conducted in FY 23-24 intended to build on past work developing a suite of invertebrate grazers that can be employed in coral co- culture, active reef restoration, or both. Specifically, we investigated the snail Lithopoma americanum, the sea urchins Diadema antillarum and Tripnuestes ventricosus, and the crabs Mithraculus coryphe and Maguimithrax spinosissimus. While L. americanum and M. coryphe were identified as having significant impediments to culture, specifically reproductive dysfunction at various points in the pre-larval life cycle, important progress was made and spawns of both species were eventually obtained. Previous limitations to spawning in T. ventricosus were overcome during this project, which allowed for insightful comparisons of growth rate between cohorts of both species. Due to their dual utility in coral co-culture as small juveniles and for direct stocking as reef grazers as larger individuals, both urchins are promising candidates. The same is true for M. spinosissimus. Grazing rates for both crab species were measured individually and in tandem, with M. spinosissimus in particular demonstrating great promise in algal control. While the project team failed to observe any successful hatches in M. coryphe until shortly before the end of the study, the observation of successful and near complete embryonic development is encouraging. The project team plans to continue working on the development of hatching and settlement techniques for the species beyond the life of the project. Further, the results of grazing assays indicate that cultured M. spinosissimus and wild M. coryphe are complementary in function rather than redundant and represent strong candidates for both co-culture with corals and for stocking onto Florida’s Coralm Reef to support and facilitate improved restoration outcomes. Ultimately, the results obtained during this project represent a positive contribution to coral reef conservation and restoration generally as well as SCTLD response specifically. Sexual propagation in land-based systems will be a vital component of SCTLD recovery in terms of rebuilding lost genetic diversity, and all of the species for which knowledge was generated in this project have demonstrated utility in co-culture of small coral recruits. Concurrently, production capacity is increasing for some of the grazer species that are of interest in direct stocking on the reef, specifically D. antillarum and M. spinosissimus. These species and others may eventually aid in addressing the macroalgal overgrowth that is hampering recovery of Florida’s Coral Reef.