31.1 Thursday, Jan. 5 Enigma of the sea urchin gut: Abiotic and biotic conditions influence form and function GIBBS, Victoria K.*; CUNNINGHAM, Adele C.; WATTS, Stephen A.; Univ. of Alabama at Birmingham; Univ. of Alabama at Birmingham; Univ. of Alabama at Birmingham email@example.com
Seasonal reproductive cycles and factors influencing gonad production have been studied for a number of sea urchin species; however, the digestive system of the sea urchin is not well understood. Gross structure and cellular composition of the regular echinoid digestive tract have been described, but study of digestive physiology is limited. We present data describing biotic factors, such as reproductive cycle, diet, and dietary lipid type, and an abiotic factor, temperature, that influence the structure and function of the gut in the regular sea urchin Lytechinus variegatus from the northern Gulf of Mexico. Seasonal changes in gut size were inversely correlated to changes in gonad size, suggesting nutrient translocation from gut reserves to gonad production. Proximate composition of the gut also changed seasonally. Gut lipid content relative to carbohydrate content was higher during winter, and gut carbohydrate content was higher relative to protein and lipid during summer. Corroborative lab studies indicate water temperature is a significant factor affecting proximate composition of the gut, gut size, and nutrient absorption efficiency. These abiotic effects may be unrelated to reproductive state. Sea urchins fed nutrient dense diets had larger guts than urchins collected from wild populations, and the quantity of lipid in the diet was positively correlated with gut size. In juveniles, gut size was larger for those fed diets containing high levels of n-3 long chain polyunsaturated fatty acids (LC-PUFA) than those fed diets containing high levels of n-6 PUFA. These data suggest both intrinsic and extrinsic factors affect gut size and composition, the consequence of which is not fully understood.