Purple sea urchins ( Strongylocentrotus purpuratus ) are an abundant urchin species in the eastern North Pacific, with a habitat range spanning the entirety of the west coast of the United States. In many areas, unchecked population growth has resulted in the destruction of kelp forests, urchins’ primary food source in the wild, and the creation of “urchin barrens”. An emerging industry of small-scale producers focused on the harvest and ranching of wild-caught urchins for the uni market provides an opportunity to diversify the domestic aquaculture sector and promote long-term aquatic ecosystem health.
For the last two years, the Bozeman Fish Technology Center (Bozeman, MT) has been working with The Nature Conservancy and UC Davis Bodega Marine Laboratory (Bodega Bay, CA) to develop an open-source diet formulation for purple urchins being cultured for the uni market. Here, we will present results from two 8-week feeding trials as well as qualitative outcomes of how select diets performed in a commercial farm setting. Feeding trial 1 tested four experimental diets (20% crude protein, 6% fat) and examined how formulations using various protein sources (marine animal, terrestrial animal, terrestrial plant, and marine plant) a ffected pellet stability, palatability, gonad growth (gonadosomatic index, GSI ), and product quality. Generally, the marine animal and marine plant formulations performed well and a blend of the two was used to develop an enhanced base formulation for use in feeding trial 2. In feeding trial 2, four experimental diets were tested against a commercially available urchin diet. The four experimental diets consisted of the enhanced base formulation as well as the base formulation with the addition of one of three different carotenoid sources: Panaferd (0.27% diet dry weight), b-carotene (20% product; 0.25% diet dry weight), or dulse (13.94%) . Generally, the experimental diets increased GSI similarly or better than the commercial diet . Further, the diets with the addition of a carotenoid source resulted in an increase in the % mango color of the uni with Panaferd and b-carotene at 40-43% and dulse at 33% compared to the base experimental diet at 20% . Currently, the availability of dried dulse is limited in the United States encouraging the use of Panaferd or b-carotene in future formulations.
Three additional feeding trials are scheduled to examine: (1) protein and starch nutrient targets, (2) ingredient selection, and (3) the use of an algae finishing diet. These upcoming initiatives and how they support the development of a domestically-available urchin diet will also be discussed.