Development of larviculture protocols for the long-spined sea urchin (Diadema antillarum) and enhanced performance with diets containing the cryptophyte Rhodomonas lens

Abstract

Slow or nonexistent natural recovery of the Caribbean long-spined sea urchin (Diadema antillarum) following a mass mortality event in [1983][1984] has prompted interest in hatchery-origin production and restocking to aid coral-reef restoration. A critical rst step is the ability to propagate D. antillarum from gametes, at scale. However, a unique larval biology and di cult and lengthy culture period of ~ 40 days has resulted in inconsistent success over the past 20-plus years. The purpose of this study was to develop protocols for rearing D. antillarum within a novel 1800-L recirculating aquaculture system capable of scaled production. Five separate experiments investigated larval development in response to diet quantity, diet composition, and initial stocking density within 40-L replicate culture tanks. The initial experiment was used to develop a microalgae reference diet consisting of Tisochrysis lutea and Chaetoceros sp. and revealed similar growth and survival between high quantity (40.0×10 3 cells ml -1 ) and low quantity (10.0×10 3 cells ml -1 ) treatments at 21 DPF. Experiments 2-4 examined diet quality by comparing carbon-equivalent microalgae compositions. Mixed diets containing Rhodomonas lens outperformed the reference diet in multiple experiments and a tripartite diet containing all three species resulted in signi cantly higher survival at 42 DPF. The highest growth overall occurred from a monoalgal R. lens diet, which indicated that this species is critically important. Further observations of density-dependent growth dynamics revealed that initial stocking densities > 1 larvae ml -1 signi cantly reduced growth over 28 DPF. Data generated were used to establish fundamental larviculture protocols that have since led to the production of over 1,000 juveniles. Adult D. antillarum were collected in March 2018 from reefs at < 8m depth off Marathon, Florida by the Florida Fish and Wildlife Research Institute under Florida Keys National Marine Sanctuary permit # FKNMS-2018-023. These broodstock were transported to a land-based restoration aquaculture facility operated by The Florida Aquarium in Apollo Beach, FL. Urchins were quarantined in a RAS within a greenhouse for 45 days. Following quarantine, 14 broodstock were transferred to 450-L berglass tanks within a 2,400-L seawater RAS. Broodstock husbandry adhered to methods previously described in Pilnick et al. (2021).Spawning was induced via thermal shock following methods described in Leber et al. (2009) andMoe (2014). Broodstock were transferred to a polyethylene tank lled with 150-L of 1-µm ltered 35 ppt arti cial seawater (ASW) (Tropic Marin, Wartenburg, Germany). Water was heated to 5°C above holding temperature and aeration was provided. Eggs were collected in a 60-mL syringe following release from females and gently rinsed in 2-L egg collectors with 35-µm mesh. Typically, males released

Effects of ethylenediaminetetraacetic acid on growth and survival of long‐spined sea urchin Diadema antillarum larvae

“…This contrasting response to EDTA exposure durations was likely due to a difference in larval density and resource allocation, i.e., at lower survival more space and food resources were available per larvae, which might have contributed to higher growth. Contrasting growth of long-spined sea urchin larvae has also been observed due to differences in larval survival in other studies (Pilnick et al 2022;Wijers et al 2023). Heavy metals induce oxidative stress during embryogenesis via production of reactive oxygen species (ROS) that lead to DNA damage and abnormal development (Rainbow 2002).…”

“…Developing a reliable large-scale larviculture technique for the long-spined sea urchin has been a longstanding challenge due to a lengthy larval duration, negative buoyancy in the culture vessel, and unique larval biology (Leber et al 2009). Novel systems for long-spined sea urchin culture have recently been developed and the nutritional requirements have been explored by our lab and collaborators (Pilnick et al 2021(Pilnick et al , 2022Hassan et al 2022;Wijers et al 2023). Several challenges remain, however, to improve larval survival to competency and metamorphosis.…”

Restoration of herbivory on Caribbean coral reefs: are fishes, urchins, or crabs the solution?

“…The larvae of D. antillarum need constant, gentle water movement during culture because they are negatively buoyant (Leber et al, 2009;Pilnick et al, 2021;Wijers et al, 2023). The microalgae Rhodomonas (either R. lens or R. salina) seems essential for rearing D. antillarum at a larval density between 0.1 and 2 larvae/mL (Eckert, 1998;Nedimyer and Moe, 2006;Pilnick et al, 2022a;Wijers et al, 2023). Improving survival of urchins during their sensitive planktonic larval and early benthic juvenile stages will be necessary for large-scale production of juvenile D. antillarum for restoration.…”

The 2022 Diadema antillarum die-off event: Comparisons with the 1983-1984 mass mortality

“…-Efforts to restore wild populations have advanced significantly since the 1983 die-off. New and developing technologies and techniques for D. antillarum rehabilitation include in-situ collection of settlers followed by head starting the settlers in the lab and restocking them on the reef as juveniles (Williams et al, 2017;Williams, 2022), new or improved culture methods (Pilnick et al, 2021;Pilnick et al, 2022;Wijers et al, 2023) and assisting natural recovery by providing suitable settlement substrate (Hylkema et al, 2022a). Except for culture, all approaches rely on natural larval supply, which may be severely reduced if upstream populations were eradicated by the 2022 die-off.…”