The long-spined sea urchin Diadema antillarum is a keystone herbivore historically responsible for reducing competitive algal overgrowth on Caribbean coral reef habitat. Limited natural population recovery following a mass mortality event in 1983-84 has inspired intensive aquaculture and restocking efforts to restore functional herbivory in support of ambitious coral reef restoration goals. Diadema is difficult to sexually propagate in captivity; culture bottlenecks during various stages of this species’ biphasic life history challenge the viability of scaled production for restoration. Here we report findings from multiple replicated investigations towards improving 1) larval settlement rate, 2) growth and survival of newly settled postlarvae (< ~2 mm test diameter (TD)), and 3) prepared diet selection for intensive juvenile (> ~2 mm TD) growout.
In an initial study, larvae reared in a novel recirculating aquaculture system for 46-49 days were transferred to replicate petri dishes and exposed to a range of potential settlement cues. Significantly higher mean percent settlement (± SE) occurred in response to the calcareous macroalgae Halimeda sp. (58.0 ± 3.7) compared to naturally derived biofilm (30.0 ± 7.1). A subsequent diet study revealed significantly improved postlarval growth response to flocculated live microalgae (flocc; 0.027mm day-1) compared to naturally derived biofilm (0.012 mm day-1) and a benthic diatom Navicula perminuta (0.023 mm day-1) over five weeks. A mixture of postlarvae and juveniles from the same cohort were then grouped by size and distributed to replicate bins containing either flocc or dried nori in a 2x2 factorial experiment. Results suggest that Diadema can be weaned onto prepared foods at ~2 mm TD. Lastly, we describe efforts to develop a water stable diet with high nutrient retention and juvenile growth response by combining blended dried nori with various concentrations (w/v) of alginate and gelatin binder. Experimental results from these efforts will be provided.