An overabundance of the pacific purple sea urchin (Strongylocentrotus purpuratus) along the central coast of California has led to an ecosystem phase shift from kelp forests to urchin barrens. Human intervention in the form of collecting purple urchins from barrens offers some relief to kelp forests, but urchins collected from barrens often do not contain a high yield of high- quality uni. These empty urchins do not have a high market value, and divers do not have an economic incentive to collect them. The collection of empty urchins from barrens and their cultivation in an aquaculture setting increases uni production in empty urchins and incentivizes people to help restore kelp forests by collecting purple sea urchins from barrens.
This study aims to determine an effective, sustainable, and accessible diet for the uni development of purple urchins collected from barrens. Trial 1 highlights the effects of varying diet crude protein (CP) and starch levels on the yield and quality of uni. The composition of the six diets includes 20% CP and 30% starch, 20% CP and 20% starch, 20% CP and 10% starch, 40% CP and 30% starch, 40% CP and 20% starch, and 40% CP and 10% starch. After 8 weeks of feeding the diets, the yield and quality of the uni was assessed. Uni yield was determined by measuring the gonad somatic index. Uni quality was measured in terms of color, firmness, and texture. The L*A*B* values of the uni color were measured using a HunterLab MiniScan EZ 4500L portable spectrophotometer. Additional L*A*B* values were determined using ImageJ software. Firmness of the uni was measured using a Food Tech Corp TMS-Pro Texture Analyzer. Subjective measurements of color, firmness, and texture were collected using a 1-4 scale, 1 being exceptional and 4 being unacceptable. Trial 2 focuses on the influence of different carotenoid sources in a purple urchin diet on the color of the uni. The carotenoids provided in each of the eight diets were beta-carotene, spirulina, dunaliella, spinach powder, astaxanthin, Panaferd, krill meal, and a control diet with no carotenoid source. These diets were fed for 8 weeks, and the yield and quality of the uni was analyzed with similar methods as Trial 1. Carotenoids in the diets were analyzed and compared to the carotenoids in the uni.
The results from this study will help to establish a feeding plan using diets that are economically and environmentally sustainable. By determining a diet for the uni development of purple urchins, this study will encourage commercial divers and aquaculturists to continue collecting urchins from barrens with the confidence that they can raise them to a marketable standard