Tissue‐Specific Macronutrient Allocation is Directly Affected by Macronutrient Intake in the Cultured Sea Urchin, Lytechinus variegatus, Nutrition Model
Authors: Yuan Yuan , Heflin Laura E , Powell Mickie L , Lawrence Addison L , Watts Stephen A 
Published: November 2023

The effect of diet on health, growth and production is a subject of intense study in humans and other vertebrate models. Interactions between dietary macronutrient intake and macronutrient allocation are a crucial component of optimized dietary design. The recent development of invertebrate models for nutritional research is likely to facilitate research designs examining the conserved interactions between dietary macronutrients and subsequent biochemical body composition. The simple and unique body organization makes the sea urchin Lytechinus variegates a great model for basic nutritional research. Many studies have examined nutritional requirements to promote growth and production among sea urchins. However, dietary macronutrients levels may also influence nutrient allocation and subsequent biochemical body composition of the primary tissues, including the gonad (primary reproductive and nutrient storage tissue), gut and test (shell) tissues.In a 10‐week growth and production trial, juvenile Lytechinus variegatus (3.95±0.54 g wet weight) were fed 6 semi‐purified formulated diets with three different protein (11, 27 and 43%) and two carbohydrate levels (12 and 18%). All other nutrient levels were held constant. Each sea urchin (n = 16 per treatment) completely consumed a sub‐satiation ration of 2.0% of the average body weight per day. Individuals were weighed and dissected at the end of 10 weeks to evaluate the gonad, gut and test.Gonad, gut and test tissues dry matter production were not correlated to dietary carbohydrate levels. However, there was a direct correlation between dietary protein levels and both gonad and test dry matter production. Individuals fed the 11% protein diet had significantly less gonad and test dry matter production than individuals fed the 27 or 43% protein diets, indicating that an adequate protein level in the diet is required for tissue production.Under the conditions of this study, significant changes in crude protein, carbohydrate and lipid content in the gonads were directly associated with dietary carbohydrate and protein levels. High protein diets were correlated with high crude protein content of the primary storage tissue (gonad), with stored protein content up to 62% dry weight. High carbohydrate diets were also correlated with increased carbohydrate content of gonads (up to 26% dry weight). Gonad lipid content ranged from 20–38% dry weight, with the highest lipid concentrations found among urchins fed the diet containing low levels of protein and carbohydrate (11P:12C). The macronutrient content of the diet did not affect the biochemical composition of somatic tissues including the gut and test. These data indicate that sea urchins have evolved nutrient storage mechanisms that allow these organisms to store dietary macronutrients when they are in excess, leading to future utilization of these macronutrients when they are not available in the diet.Support or Funding InformationThis research supported in part by the Aquatic Animal Research Core, NIH NORC P30DK056336.