WALLACE, B.D.*; HAMMER, H.S.; WATTS, S.A.; LAWRENCE, J.M.; LAWRENCE, A.L.: The effects of dietary protein concentration on growth of juveniles of the sea urchin Lytechinus variegatus .

Juveniles (ca. 14 mm diameter, n=120) were collected at St. Joseph Bay, FL in March 2000. They were held in 80 L aquaria with artificial seawater at 21 C and 32 ppt salinity. The juveniles were fed ad libitum one of four isocaloric diets varying in protein concentration (14, 23, 32 or 50%) for 14 weeks. Test diameters increased from 14 mm to 19.8, 29.4, 30.5, or 32.6 mm in individuals fed the 14, 23, 32, or 50 % protein diet, respectively. Total wet weights increased from 1.06 g to 4.7, 13.7, 14.4, or 16.5 g in individuals fed the 14, 23, 32, or 50 % protein diet, respectively. Specific growth rates were 1.7, 2.9, 2.9, or 3.1 % body wet weight increase per day. At week 14, gonad indices (wet gonad/wet weight x 100) were 2.5, 7.4, 7.2 or 9.1 for the 14, 23, 32, or 50 % protein diet, respectively. Apparent dry matter digestibility, measured on week 5 and 10, ranged from 83 to 90 % (lowest in those fed the low protein diet) and did not change over time. Survivorship was 100% in individuals fed the 32 or 50 % protein diet, but was reduced to 77 or 70 % in those fed the 14 or 23 % protein diet. Low concentrations of dietary protein influenced growth rate, gonad production, and survivorship, but had minimal influence on absorption efficiency. Gonad production occurred in individuals whose diameters were smaller than reported previously in field populations. The requirement for a protein diet of > 23 % corroborates with ecological studies that indicate L. variegatus preferentially consumes epibionts and animal tissues in preference to seagrasses. Funded by Mississippi-Alabama Sea Grant.