Effect of prepared and macroalgal diets and seed stock source on somatic growth of juvenile green sea urchins (Strongylocentrotus droebachiensis ) T.L. Daggett a, * , C.M. Pearce a,1 , M. Tingley b , S.M.C. Robinson c , T. Chopin d a Ross Island Salmon Ltd., P.O. Box 1304, Grand Manan, New Brunswick, Canada E5G 4M9 b Department of Mathematics and Statistics, University of New Brunswick, P.O. Box 4400, Fredericton, New Brunswick, Canada E3B 5A3 c Shellfish Aquaculture Division, Fisheries and Oceans Canada, St. Andrews Biological Station, 531 Brandy Cove Rd., St. Andrews, New Brunswick, Canada E5B 2L9 d Centre for Coastal Studies and Aquaculture, Department of Biology, University of New Brunswick Saint John, P.O. Box 5050, Saint John, New Brunswick, Canada E2L 4L5 Received 28 May 2004; received in revised form 29 November 2004; accepted 29 November 2004 Abstract Populations of sea urchins, harvested for their gonads, are in decline worldwide and so scientific research is now focusing on full life cycle grow-out. The objective of this study was to compare the growth rates of juvenile (initial test diameter: 4.5–13.7 mm) green sea urchins that were held in laboratory tanks and fed a variety of diets. Two separate experiments were conducted. The first compared juvenile growth on seven different diets: 1) prepared diet, 2) Porphyra purpurea , 3) Palmaria palmata, 4) Ulva linza, 5) a mixture of Ulvaria obscura and Ulva lactuca , 6) Laminaria saccharina collected from an Atlantic salmon aquaculture site, and 7) L. saccharina collected from a site relatively distant from salmon aquaculture operations. The latter two treatments were chosen in order to determine if the nutrient regime in which an alga was grown could affect juvenile growth rate. A second experiment compared the growth rates of wild-caught and hatchery-reared juvenile green sea urchins fed either a prepared diet or fresh kelp (L. saccharina ) collected from a site relatively distant from salmon aquaculture. Test diameter and whole wet weight measurements were taken monthly for a period of 16 months. In the first experiment, feed type significantly affected somatic growth rate, the overall best growth being supported by Porphyra purpurea (mean growth rate FSE: 0.059F0.001 mm d 1 ) and the prepared diet (0.056F0.001 mm d 1 ). L. saccharina collected from the site distant from salmon aquaculture operations (0.019F0.001 mm d 1 ) produced significantly slower growth than any other feeding treatment including L. saccharina collected from a salmon aquaculture site (0.047F0.001 mm d 1 ). In the second experiment, feed type also significantly affected growth with the prepared diet (0.058F0.001 mm d 1 ) supporting better growth than L. saccharina 0044-8486/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2004.11.030 * Corresponding author. Present address: 1287 Route 776, Grand Manan, New Brunswick, Canada E5G 1G4. Tel.: +1 506 662 9890; fax: +1 506 662 3093. E-mail address: tdaggett@simcorp.ca (T.L. Daggett). 1 Present address: Fisheries and Oceans Canada, Pacific Biological Station, 3190 Hammond Bay Road, Nanaimo, British Columbia, Canada V9T 6N7. Aquaculture 244 (2005) 263 – 281 www.elsevier.com/locate/aqua-online