A novel system for intensive Diadema antillarum propagation as a step towards population enhancement

Abstract

The long-spined sea urchin Diadema antillarum was once an abundant reef grazing herbivore throughout the Caribbean. During the early 1980s, D. antillarum populations were reduced by > 93% due to an undescribed disease. This event resulted in a lack of functional reef herbivory and contributed to ongoing ecological shifts from hard coral towards macroalgae dominated reefs. Limited natural recovery has increased interest in a range of strategies for augmenting herbivory. An area of focus has been developing scalable ex situ methods for rearing D. antillarum from gametes. The ultimate use of such a tool would be exploring hatchery origin restocking strategies. Intensive ex situ aquaculture is a potentially viable, yet difficult, method for producing D. antillarum at scales necessary to facilitate restocking. Here we describe a purpose-built, novel recirculating aquaculture system and the broodstock management and larval culture process that has produced multiple D. antillarum cohorts, and which has the potential for practical application in a dedicated hatchery setting. Adult animals held in captivity can be induced to spawn year-round, with some evidence for annual and lunar periodicity. Fecundity and fertilization rates are both consistently very high, yet challenges persist in both late stage larval development and early post-settlement survival. Initial success was realized with production of 100 juvenile D. antillarum from ~ 1200 competent larvae. While the system we describe requires a significant level of investment and technical expertise, this work advances D. antillarum culture efforts in potential future hatchery settings and improves the viability of scalable ex situ production for population enhancement.

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

“…Larval rearing followed the methods established in Pilnick et al (2021). Fewer than 1 million embryos were incubated at 25-26°C in semi-circular 40-L culture tanks with pulsed aeration.…”

“…Still, speculative factors including environmental toxins, water quality, and general culture methods precluded reliable development through metamorphosis (Leber et al, 2009). Outstanding restoration goals led to the development of a novel recirculating aquaculture system (RAS) to investigate larviculture bottlenecks and improve the feasibility of scaled production (Pilnick et al, 2021). These culture efforts represented the rst attempt to culture D. antillarum within a RAS and has to-date produced over 1,000 juveniles.…”

“…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).…”

“…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).…”

Assisted Natural Recovery: A Novel Approach to Enhance Diadema antillarum Recruitment

“…Three different methods have so far been attempted to help restore D. antillarum populations, and all rely on the restocking of juvenile or adult individuals. These are either obtained by translocating wild D. antillarum from recovered populations (Macía et al, 2007;Burdick, 2008;Dame, 2008), by collecting settlers and headstarting them till the juvenile stage in a landbased nursery (Williams, 2017;Williams, 2022) or by culturing juveniles in captivity through their larval stages starting from gametes (Pilnick et al, 2021;Wijers et al in prep).…”