Addison L. Lawrence

Feeding, Digestion and Digestibility of Sea Urchins

Abstract Sea urchins are omnivores. In the field, they consume the food that is available, although they do have preferences when a choice is present. This results from attractants, incitants, stimulants and deterrents present in potential food, and also its physical characteristics. Abiotic factors such as hydrodynamics, light and temperature and biological factors such as their physiological, nutritional, reproductive state and body size affect feeding. The basic array of digestive enzymes is present, but sea urchins have little capacity to digest insoluble structural carbohydrates. This affects digestibility and capacity for production. Information about feeding, digestion and digestibility is essential to understand the biology and ecology of sea urchins and to develop feeds for their aquaculture.

Chapter 10 – Nutrition

This chapter describes factors affecting nutrition, basic procedures that should be employed to study nutrition, and a synopsis of the current state of knowledge. We are on the frontier of sea urchin nutrition research and feed development. In recent years, much of the interest in understanding sea urchin nutrition has been motivated by interest in aquaculture. Much more research is needed before we know daily quantitative nutritional requirements for defined culture conditions, have clear and concise answers to questions pertaining to the role of specific nutrients in sea urchin biology, and formulate cost-effective, nutritionally complete, and environmentally friendly feeds. Recent advances in molecular technologies have the potential to revolutionize our knowledge of nutrient effects and interactions.

Production and economic optimization of dietary protein and carbohydrate in the culture of Juvenile Sea Urchin Lytechinus variegatus

Juvenile Lytechinus variegatus (ca. 3.95± 0.54 g) were fed one of 10 formulated diets with different protein (ranging from 11- 43%) and carbohydrate (12 or 18%; brackets determined from previous studies) levels. Urchins (n= 16 per treatment) were fed a daily sub-satiation ration equivalent to 2.0% of average body weight for 10 weeks. Our objective was (1) to create predictive models of growth, production and efficiency outcomes and (2) to generate economic analysis models in relation to these dietary outcomes for juvenile L. variegatus held in culture. At dietary protein levels below ca. 30%, models for most growth and production outcomes predicted increased rates of growth and production among urchins fed diets containing 18% dietary carbohydrate levels as compared to urchins fed diets containing 12% dietary carbohydrate. For most outcomes, growth and production was predicted to increase with increasing level of dietary protein up to ca. 30%, after which, no further increase in growth and production were predicted. Likewise, dry matter production efficiency was predicted to increase with increasing protein level up to ca. 30%, with urchins fed diets with 18% carbohydrate exhibiting greater efficiency than those fed diets with 12% carbohydrate. The energetic cost of dry matter production was optimal at protein levels less than those required for maximal weight gain and gonad production, suggesting an increased energetic cost (decreased energy efficiency) is required to increase gonad production relative to somatic growth. Economic analysis models predict when cost of feed ingredients are low, the lowest cost per gram of wet weight gain will occur at 18% dietary carbohydrate and ca. 25- 30% dietary protein. In contrast, lowest cost per gram of wet weight gain will occur at 12% dietary carbohydrate and ca. 35- 40% dietary protein when feed ingredient costs are high or average. For both 18 and 12% levels of dietary carbohydrate, cost per gram of wet weight gain is predicted to be maximized at low dietary protein levels, regardless of feed ingredient costs. These models will compare dietary requirements and growth outcomes in relation to economic costs and provide insight for future commercialization of sea urchin aquaculture.