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.

Figure 1

Conceptual model illustrating D. antillarum restocking via hatchery produced animals. Stages include in situ broodstock collection from wild populations, ex situ broodstock maintenance, larval development within scalable hatchery production settings, settlement and juvenile growout, and in situ restocking on targeted coral reefs. Arrow colors depict current levels of success in achieving each stage; green = achieved reliably at large scale, yellow = achieved somewhat reliably at reduced scale, red = not yet tested. The transition from green to yellow depicts a shift from reliable, successful production of hundreds of thousands of late-stage larvae to relatively fewer metamorphically competent larvae at 28–35 DPF (days post fertilization). Figure by Joseph A. Henry.

Figure 2

Photograph depicting configuration of the 1800-L recirculating larviculture system used to rear D. antillarum larvae.

Figure 3

Representative photographs of D. antillarum development at (a) 2 h post fertilization, first cell division, D = 80 µm, (b) 36 h post fertilization, late gastrula/prism, mid body length (MBL) = 85 µm, (c) 3 d post fertilization, early pluteus larvae, MBL = 90 µm, appendage length (AL) = 190 µm, (d) 21 d post fertilization, 4-armed echinopluteus transversus larvae, MBL = 250 µm, AL = 2000 µm, (e) 28 d post fertilization, metamorphically competent late pluteus larvae with adult rudiment and extended tube feet, MBL = 600 µm, (f) 36 d post fertilization, mid-metamorphic radially symmetrical juvenile resorbing bilaterally symmetrical larval structure, D = 850 µm, (g) 36 d post fertilization, settled juvenile, D = 900 µm, (h) 248 d post fertilization, hatchery reared D. antillarum, D = 1–3 cm.