24 MARCH 2022 • WORLD AQUACULTURE • WWW.WA S .ORG over the past ~20 years due to an extremely difficult and lengthy larval culture process of around 40 days and lack of existing information. Beginning in 2018, researchers based at the Florida Aquarium Center for Conservation (CFC) in Apollo Beach have been working to address these knowledge gaps. Although commercial echinoderm aquaculture methods are well established, aspects of long-spined sea urchin larval biology are unique and prevent application of these general methods for successful development in culture. Primarily, the negatively buoyant and mechanically fragile echinopluteus larvae necessitated the creation of a unique semicircular culture vessel with pulsed aeration (Leber et al. 2008, Moe 2014). Long-spined sea urchin also exhibit extreme sensitivity to water quality, specifically dissolved heavy metals (Bielmyer et al. 2005), and likely have specific nutritional requirements (Eckert 1998). A novel experimental recirculating system was designed and built at the CFC to investigate appropriate larval diet requirements within a hatchery production setting (Pilnick et al. 2021). An initial trial established a reference diet containing two microalgae species, Tisochrysis lutea and Chaetoceros sp., and compared larval success between a high density (40,000 cells/mL) diet and a low density (10,000 cells/mL) diet over 21 days-post fertilization. The average larval growth rate per day was 6.6 percent in the high-density treatment, however larval body size and survival was similar overall between treatments. Further experimentation comparing the effects of different carbon-equivalent microalgae diet combinations revealed enhanced performance from specific diets. In one experiment, two diets containing Rhodomonas lens resulted in significantly larger larvae and a higher proportion of surviving larvae compared to the reference diet after 21-days post-fertilization. Data generated were used to establish fundamental larviculture protocols that have since produced over 700 juvenile long-spined sea urchin (Fig. 8). Although these efforts represent the most successful instances of longspined sea urchin aquaculture to date, more research is needed before being able to fully implement a successful hatchery production process for restoration. Roe Enhancement of the Purple Sea Urchin Collected from Barren Grounds and Fed Prepared Diets Renee E. Angwin, Brian T. Hentschel and Todd W. Anderson Sea urchins are an edible delicacy worldwide. Also known as uni or roe, urchin gonads are a highly prized seafood in Europe and Asia, especially in Japan. Only 17 of the over 850 species of urchins are commercially valuable, and only two of those – red urchin Mesocentrotus franciscanus and purple urchin Strongylocentrotus purpuratus – are native to the west coast of the United States (Harris and Eddy 2015). The red sea urchin fishery began in 1971 in southern California to develop an underutilized species and to curb destructive grazing on giant kelp (Kalvass and RogersBennet 2002). In contrast, purple sea urchins have very limited commercial value due to their smaller size and lower roe yield, and a robust fishery for purple urchins has not yet fully developed (Parker and Ebert 2002). Purple urchins have long been considered a pest because they voraciously consume kelp (Parker and Ebert 2002, House et al. 2017). In recent years, overgrazing by purple urchins has transformed lush kelp forests into barren grounds devoid of kelp and associated inhabitants (Ling et al. 2015, Filbee-Dexter and Scheibling 2014). This formation of urchin barrens has been largely attributed to the loss of top predators and increasing oceanic temperatures, both of which create opportunistic windows for urchins to overgraze kelp habitat as natural controls and sources FIGURE 8. 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. Reprinted from Pilnick et al. (2021), https://www.nature.com/articles/s41598-021-90564-1.
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