WWW.WA S .ORG • WORLD AQUACULTURE • MARCH 2022 25 ( C O N T I N U E D O N P A G E 2 6 ) of kelp replenishment are altered (Ling et al. 2015, Filbee-Dexter and Scheibling 2014). Along the California coast, high densities of purple urchins have resulted in more than 93 percent loss of kelp in some locations (CDFW Aerial Kelp Surveys 2016). These herbivores subsist on very little food and can rapidly acclimate to adverse conditions, making them challenging to control (Kelly et al. 2013, Ling et al. 2015). Catastrophic regime shifts to urchin barrens are difficult to reverse; virtually all urchins must be removed to facilitate the return of kelp (Ling et al. 2015), which can only occur through severe disturbance (Ebeling et al. 1985). Malnourished purple urchins within barrens (Fig. 9) have little to no roe and presently have no economic value. With global catches of commercially harvested urchin species in decline, interest in urchin aquaculture, also known as echinoculture, has been increasing (LiyanaPathirana et al. 2002, Dale et al. 2005, Cuesta-Gomez and Sanchez-Saavedra 2017, 2018, Baiao et al. 2019). Removing purple urchins from barrens and ranching them for roe enhancement can create an economically viable product that also contributes to kelp forest restoration. Using land-based aquaculture techniques in conjunction with specially formulated prepared feeds, barren urchins can be transformed from empty, malnourished pests into roe-rich seafood in less than ten weeks (Gagnon et al. 2017, James et al. 2017). Roe enhancement is more economically sustainable than traditional echinoculture that begins with larvae that require up to three years to grow to adult size (Eddy et al. 2015, Walker et al. 2015), and trials have shown promising results with Evechinus chloroticus in New Zealand (James 2006), Strongylocentrotus droebachiensis in Norway and Canada (James et al. 2017, Gagnon et al. 2017), and Loxechinus albus in Chile (Lawrence et al. 1997). Roe enhancement is not currently employed in the United States and has not been tested rigorously on S. purpuratus. The recent expansion of barrens caused by overabundant purple urchins provides an enormous opportunity to sustainably exploit these high-density populations and transform their lowquality gonads into a valued seafood resource. The outcome of such an opportunity can help reinvigorate the California urchin industry, restore kelp forests from degraded barrens and enhance the ecosystem services kelp forests provide to impacted coastal communities. In this study, we collected purple urchins from barrens and fed them whole kelp or two different formulations of algal-based prepared feed in a recirculating aquaculture system (RAS). The gonad index (GI) of urchins fed the two prepared diets doubled in 6 weeks, increased from a barren condition to a marketable yield (GI > 15 percent) in nine weeks (Fig. 9), and was significantly greater than the GI of urchins fed kelp. Analyses of proximate constituents and amino acid composition of gonad tissue also revealed differences among the roe of urchins fed the three diets for 9 weeks. In particular, one of the two prepared feeds resulted in a significantly greater amount of bitter-tasting amino acids in enhanced gonads compared to urchins fed kelp, while the other prepared formulation indicated a more natural flavor profile, suggesting superior suitability for commercial applications. Our results highlight an untapped potential to produce quickly a highly valued seafood product from seemingly low-value purple urchins. Echinoculture could thereby serve as a tool to stimulate urchin industries that also facilitates the restoration of kelp forests from urchin barrens. Purple Urchin Barrens: An Opportunity for Aquaculture and Fisheries toWork Together to Solve an Environmental Issue Luke Gardner, Helaina Lindsey, Katherine Neylan, Walan Chang, Katrina Herrmann, Max Rintoul and Katherine Roy Sea urchin barrens are characterized by an overabundance of sea urchins and coralline algae where kelp forests once dominated a marine ecosystem. The prevalence and duration of these barrens appears to be increasing globally on temperate coastlines. This is of concern for marine resource managers as the barrens generally result in a reduction in habitat diversity and productivity. Recently, California and Oregon, USA, are undergoing an ecosystem switch from kelp forests to urchin barrens, which are persisting and expanding from the Central California coast north into Oregon. Significant reduction of urchin populations from barrens usually results in restoration of kelp forests. However, the large geographical scale of this barren represents a logistical challenge for economic urchin removal. Conventional fisheries mediated FIGURE 9. (Left) A typical barren urchin at the start of the 9-wk experiment. Miniscule gonads are thin orange streaks lining the aboral surface of the inner test. (Right) A typical urchin after 9 weeks on a prepared diet. Plump orange gonads (roe, uni) have developed to a marketable size. FIGURE 10. Week 1 (left) vs. week 10 (right) after culture of purple urchins in an aquaculture system fed different diets. The urchin on the left is representative of the starting gonad condition of the study (gonads are indistinguishable) and is typical of purple urchin inhabiting an urchin barren. The urchin on the right was fed the formulated diet resulting in a gonad condition that is commercial marketable.
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